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| United States Patent |
6,383,815
|
|
Potyrailo
|
May 7, 2002
|
Devices and methods for measurements of barrier properties of coating
arrays
Abstract
Methods and devices are disclosed for measuring barrier properties of a
barrier coating or coating arrays where each barrier coating has a small
cross section. To reduce the edge effects in the measurements of barrier
properties, measurements are made using a waveguide structure that
includes at least one waveguide coated with a chemically sensitive layer
and an array of barrier coatings. The coated waveguide is exposed to a
material of interest that has the ability to produce an analyzable
variation in the chemically sensitive layer, thereby providing the ability
to detect an impact of the material of interest on the barrier coatings.
In one variation, an initial light wave is propagated within the waveguide
structure, a resulting wave associated with the initial wave and each
barrier coating is detected, and any impacts on the coatings by the
material of interest are correlated to a value of a barrier property for
each of the array of barrier coatings.
| Inventors:
|
Potyrailo; Radislav Alexandrovich (Niskayuna, NY)
|
| Assignee:
|
General Electric Company (Schenectady, NY)
|
| Appl. No.:
|
681432 |
| Filed:
|
April 4, 2001 |
| Current U.S. Class: |
436/2; 422/82.08; 422/82.11; 436/5; 436/172 |
| Intern'l Class: |
G01N 021/64 |
| Field of Search: |
436/2,5,172
422/82.08,82.11
|
References Cited [Referenced By]
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| |
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|
Primary Examiner: Snay; Jeffrey
Attorney, Agent or Firm: Johnson; Noreen C., Cabou; Christian G.
Goverment Interests
FEDERAL RESEARCH STATEMENT
The U.S. Government may have certain rights in this invention pursuant to
contract number 70NANB9H3038 awarded by the National Institutes of
Standards and Technology (NIST).
Claims
What is claimed is:
1. A device for measurement of barrier properties of barrier coatings, the
device comprising:
at least one waveguide having an external surface;
a chemically sensitive layer disposed about the external surface of the at
least one waveguide, the chemically sensitive layer responsive to a
material of interest;
a predefined number of barrier coatings deposited onto the chemically
sensitive layer, each of the barrier coatings having a corresponding
barrier property with respect to the material of interest;
a light source operable to propagate a wave within the at least one
waveguide;
a detector operable to measure impacts associated with the propagated wave,
the impacts associated with the respective barrier property of each of the
predefined number of barrier coatings; and
a correlator for correlating the measured impact with a value of the
barrier property for each of the predefined number of barrier coatings.
2. The device of claim 1, wherein the predefined number of barrier coatings
is one coating.
3. The device of claim 1, wherein the predefined number of barrier coatings
is a plurality of coatings comprising a combinatorial array.
4. The device of claim 1, wherein the impacts are associated with a
detected wave that is forward-propagated.
5. The device of claim 1, wherein the impacts are associated with a
detected wave that is back-propagated.
6. The device of claim 1, wherein the at least one waveguide comprises an
optical fiber and wherein each of the plurality of barrier coatings extend
circumferentially about the waveguide in a spaced apart relationship.
7. The device of claim 6, wherein the at least one waveguide comprises a
plurality of waveguides, wherein one of the plurality of barrier coatings
is deposited on a corresponding one of the plurality of waveguides.
8. The device of claim 1, wherein the at least one waveguide comprises an
optical fiber and wherein each of the plurality of barrier coatings extend
circumferentially about the at least one waveguide and are adjacently
positioned lengthwise along the waveguide such that there is no space
between the coatings.
9. The device of claim 8, wherein the at least one waveguide comprises a
plurality of waveguides, wherein one of the plurality of barrier coatings
is deposited on a corresponding one of the plurality of waveguides.
10. The device of claim 1, wherein the plurality of barrier coatings each
have a different predetermined parameter and a predetermined location
lengthwise along the waveguide.
11. The device of claim 10, wherein the predetermined parameter is selected
from the group consisting of composition, thickness, and coating
preparation and/or storing and/or application conditions.
12. The device of claim 1, wherein the impacts measured by the detector is
selected from the group consisting of an amplitude, a frequency, a
polarization state, a phase, a temporal property, and combinations
thereof.
13. The device of claim 1, wherein the barrier property comprises
permeability.
14. The device of claim 1, wherein the chemically sensitive layer comprises
a fluorophore.
15. The device of claim 1, wherein the chemically sensitive layer comprises
a colorimetric reagent.
16. The device of claim 1, wherein the chemically sensitive layer comprises
a polymeric material.
17. The device of claim 1, wherein the chemically sensitive layer comprises
an inorganic material.
18. The device of claim 1, wherein the chemically sensitive layer comprises
a sol-gel material.
19. The device of claim 1, wherein the predetermined number of barrier
coatings comprise inorganic materials.
20. The device of claim 1, wherein the predetermined number of barrier
coatings comprise organic materials.
21. The device of claim 1, wherein the predetermined number of barrier
coatings comprise organic and inorganic materials.
22. The device of claim 1, wherein the predetermined number of barrier
coatings are selected from the group consisting of oxides, nitrides and
oxinitrides of silicon, aluminum, zinc, boron and other metals, ceramics,
polyvinyl alcohol, ethylene vinyl alcohol copolymers, polyvinyl
dichloride, different types of nylon, acrylics, cellophane, silicones,
polyethylene terephtalate, PVC, PCTFE, polypropylene, sol-gels, and
combinations thereof.
23. The device of claim 1, wherein the at least one waveguide, the
chemically sensitive layer coating, and the predetermined number of
barrier coatings comprise a waveguide structure; and the device further
comprises a cell for containing the waveguide structure and the material
of interest.
24. The device of claim 1, wherein the wave propagated by the light source
further comprises a pulsed wave associated with a given time, and wherein
the correlator includes a processor for determining a variation between
the pulsed wave and the impacted wave and for correlating the determined
variation with one of the plurality of barrier coatings based on the given
time of the pulsed wave.
25. The device of claim 1, wherein the material of interest is selected
from the group consisting of oxygen, water, water vapor, organic and
inorganic vapors and combinations thereof.
26. The device of claim 1, wherein the impacts on the propagated wave are
associated with a change in a chemically sensitive layer characteristic
selected from the group consisting of absorption spectrum, refractive
index, luminescence intensity, luminescence lifetime, luminescence
spectrum and combinations thereof.
27. The device of claim 1, wherein the chemically sensitive layer comprises
a thin film having a thickness in the range of about 0.05 to about 1000
micrometers.
28. The device of claim 1, wherein each of the plurality of barrier
coatings comprises a thin film having a thickness in the range of about
0.1 nanometers to about 100 micrometers.
29. The device of claim 1, wherein the propagated wave produced by the
light source has a spectral range of emission from about 150 nanometers to
about 2500 nanometers.
30. A device for measurement of barrier properties of barrier coatings, the
device comprising:
at least one waveguide extending lengthwise and having an external surface;
a chemically sensitive layer disposed about the circumference of the
external surface of at least a portion of the at least one waveguide, the
chemically sensitive layer responsive to a material of interest;
a plurality of barrier coatings deposited onto the chemically sensitive
layer such that each coating extends circumferentially about the at least
one waveguide, each of the barrier coatings having a corresponding barrier
property with respect to the material of interest;
a light source operable to propagate a pulsed wave associated with a given
time within the at least one waveguide;
a detector operable to measure impacts associated with the propagated wave
and associated with the respective barrier property of each of the
plurality of barrier coatings; and
a processor for determining a value of the barrier property associated with
the measured impact and for correlating the value of the barrier property
with each of the plurality of barrier coatings.
31. The device of claim 30, wherein the at least one waveguide comprises an
optical fiber and wherein each of the plurality of barrier coatings extend
circumferentially about the waveguide and are adjacently positioned
lengthwise along the waveguide such that there is no space between the
coatings.
32. The device of claim 30, wherein the impacts on the propagated wave
measured by the detector is selected from the group consisting of an
amplitude, a frequency, a polarization state, a phase, a temporal
property, and combinations thereof.
33. The device of claim 30, wherein the barrier property comprises
permeability.
34. The device of claim 30, wherein the at least one waveguide, the
chemically sensitive layer coating, and the plurality of barrier coatings
comprise a waveguide structure; and the device further comprises a cell
for containing the waveguide structure and the material of interest.
35. The device of claim 30, wherein the material of interest is selected
from the group consisting of oxygen, moisture, water vapor, organic and
inorganic vapors and combinations thereof.
36. The device of claim 30, wherein the impacts on the propagated wave are
associated with a change in a chemically sensitive layer characteristic
selected from the group consisting of absorption spectrum, refractive
index, luminescence intensity, luminescence lifetime, luminescence
spectrum and combinations thereof.
37. The device of claim 30, wherein the chemically sensitive layer
comprises a polymeric or inorganic or composite material.
38. The device of claim 30, wherein the chemically sensitive layer
comprises a polymeric material having a sufficient combination of response
time, material of interest permeability, material of interest solubility,
and degree of transparency and hardness relative to the material of
interest and the analyzed barrier property.
39. The device of claim 30, wherein the chemically sensitive layer
comprises a dynamically quenched luminescent reagent.
40. The device of claim 30, wherein the chemically sensitive layer
comprises a statically quenched luminescent reagent.
41. The device of claim 30, wherein the chemically sensitive layer
comprises a colorimetric reagent.
42. The device of claim 30, wherein the chemically sensitive layer
comprises a combination of colorimetric and luminescent reagents.
43. The device of claim 30, wherein the chemically sensitive layer
comprises a combination of analyte-sensitive colorimetric reagent and
analyte-insensitive luminescent reagent.
44. The device of claim 30, wherein the chemically sensitive layer
comprises a oxygen-sensitive reagent.
45. The device of claim 30, wherein the chemically sensitive layer
comprises a moisture-sensitive reagent.
46. The device of claim 30, wherein the chemically sensitive layer
comprises a luminescent reagent selected from the group consisting of a
porphyrin, a polycyclic aromatic hydrocarbon, a long-wave absorbing dye, a
metal organic complex of ruthenium, a metal organic complex of osmium, a
metal organic complex of iridium, a metal organic complex of gold, and a
metal organic complex of platinum.
47. The device of claim 30, wherein the chemically sensitive layer
comprises a solvatochromic reagent.
48. The device of claim 30, wherein the chemically sensitive layer
comprises a pH reagent.
49. The device of claim 30, wherein the chemically sensitive layer
comprises a thin film having a thickness in the range of about 0.5 to
about 100 micrometers.
50. The device of claim 30, wherein each of the predefined number of
barrier coatings comprises a thin film having a thickness in the range of
about 1 nanometer to about 10 micrometers.
51. The device of claim 30, wherein the propagated wave produced by the
light source has a spectral range of emission from about 150 nanometers to
about 2500 nanometers.
52. A method for measuring barrier properties of coating arrays, the method
comprising:
applying a chemically sensitive layer to an exterior surface of at least
one waveguide, where the chemically sensitive layer has at least one
characteristic that changes in response to exposure to a material of
interest;
applying a predefined number of barrier coatings to the chemically
sensitive layer, each of the predefined number of barrier coatings having
a barrier property with respect to the material of interest;
transmitting a wave through the at least one waveguide;
exposing the at least one coated waveguide to the material of interest;
detecting an impact associated with the propagated wave and the material of
interest; and
correlating the detected impact with a value of a barrier property for each
of the array of barrier coatings.
53. The method of claim 52, where applying the barrier coatings to the
chemically sensitive layer further comprises applying each of the barrier
coatings about the circumference of the at least one waveguide.
54. The method of claim 53, where the at least one waveguide comprises a
plurality of waveguides, and where one of the plurality of barrier
coatings is deposited on a corresponding one of the plurality of
waveguides.
55. The method of claim 52, where applying the barrier coatings to the
chemically sensitive layer further comprises applying each of the barrier
coatings about the circumference of the at least one waveguide in an
abutting relationship.
56. The method of claim 55, where the at least one waveguide comprises a
plurality of waveguides, and where one of the plurality of barrier
coatings is deposited on a corresponding one of the plurality of
waveguides.
57. The method of claim 52, where the barrier property comprises
permeability.
58. The method of claim 52, where the chemically sensitive layer comprises
a luminescent reagent.
59. The method of claim 52, where the chemically sensitive layer comprises
a polymeric material.
60. The method of claim 52, where the predefined number of barrier coatings
are selected from the group consisting of oxides, nitrides and oxinitrides
of silicon, aluminum, zinc, boron and other metals, ceramics, polyvinyl
alcohol, ethylene vinyl alcohol copolymers, polyvinyl dichloride,
different types of nylon, acrylics, cellophane, polyethylene terephtalate,
PVC, PCTFE, polypropylene, sol-gels and combinations thereof.
61. The method of claim 52, further comprising containing the at least one
waveguide with the chemically sensitive layer coating and the predefined
number of barrier coatings and the material of interest within a cell.
62. The method of claim 52, where the material of interest is selected from
the group consisting of oxygen, water, moisture, water vapor, organic and
inorganic vapors and combinations thereof.
63. The method of claim 52, where the impacts on the propagated wave are
associated with a change in a chemically sensitive layer characteristic
selected from the group consisting of absorption spectrum, refractive
index, luminescence intensity, luminescence lifetime, luminescence
spectrum and combinations thereof.
64. The method of claim 52, where detecting an impact associated with the
propagated wave and the material of interest further comprises determining
a difference in characteristic of a forward-propagated wave and an
associated back-propagated wave.
65. A method for measuring barrier properties of coating arrays, the method
comprising:
applying a chemically sensitive layer about the circumference of an
exterior surface of at least one waveguide, where the chemically sensitive
layer has at least one characteristic that changes in response to exposure
to a material of interest;
applying an array of barrier coatings to the chemically sensitive layer
such that the barrier coatings extend about the circumference of the at
least one waveguide, each of the array of barrier coatings having a
barrier property with respect to the material of interest;
transmitting a first wave through the at least one waveguide;
detecting a first resultant wave associated with the first wave and each of
the array of barrier coatings;
exposing the at least one waveguide with the applied array of barrier
coatings to the material of interest;
transmitting a second wave through the at least one waveguide;
detecting a second resultant wave associated with the second wave and each
of the array of barrier coatings;
determining an impact associated with a difference between the first
resultant wave and the second resultant wave for each of the array of
barrier coatings; and
correlating the impact with a value of a barrier property for each of the
array of barrier coatings.
66. The method of claim 65, where applying the barrier coatings to the
chemically sensitive layer further comprises applying each of the barrier
coatings in an abutting relationship.
67. The method of claim 65, where the barrier property comprises
permeability.
68. The method of claim 65, where the chemically sensitive layer comprises
a luminescent reagent incorporated into a polymeric material.
69. The method of claim 65, where the chemically sensitive layer comprises
a luminescent reagent incorporated into an inorganic material.
70. The method of claim 65, where the chemically sensitive layer comprises
a colorimetric dye incorporated into a polymeric material.
71. The method of claim 65, where the chemically sensitive layer comprises
a colorimetric dye incorporated into an inorganic material.
72. The method of claim 65, where the array of barrier coatings is selected
from the group consisting of oxides, nitrides and oxinitrides of silicon,
aluminum, zinc, boron and other metals, ceramics, polyvinyl alcohol,
ethylene vinyl alcohol copolymers, polyvinyl dichloride, different types
of nylon, acrylics, cellophane, polyethylene terephtalate, PVC, PCTFE,
polypropylene, sol-gels and combinations thereof.
73. The method of claim 65, further comprising containing the at least one
waveguide with the chemically sensitive layer coating and the array of
barrier coatings and the material of interest within a cell.
74. The method of claim 65, where the material of interest is selected from
the group consisting of oxygen, water, moisture, water vapor, organic and
inorganic vapors and combinations thereof.
75. The method of claim 65, where the impact is associated with a change in
a chemically sensitive layer characteristic selected from the group
consisting of absorption spectrum, refractive index, luminescence
intensity, luminescence lifetime, luminescence spectrum and combinations
thereof.
76. The method of claim 65, where the at least one waveguide comprises a
plurality of waveguides, and where one of the plurality of barrier
coatings is deposited on a corresponding one of the plurality of
waveguides.
Description
BACKGROUND OF INVENTION
The invention relates to devices and methods for determining barrier
properties of coatings, and more particularly, to combinatorial barrier
property screening devices and methods.
Coatings having barrier properties are used for many packaging and
protective applications. The coatings, as barriers, typically separate a
system, such as an electronic component, a part of an engineering
structure or an article of food, from an environment. As such, the barrier
properties of the coating define the permeability or resistance of the
particular coating to a given material of interest. For example, typical
barrier properties include the resistance of a coating to oxygen or to
moisture.
In an effort to discover new and improved coating formulations, the
analysis of new coatings is limited by the large sample sizes and long
exposure time periods typically required for screening each new coating
formulation. The large sample size and long exposure times to one or more
materials of interest to test a coating formulation are generally required
in order to detect the transport of the material of interest through the
coating. Because the barrier properties of a coating may be high, only
small amounts of the material of interest may penetrate the coating and/or
it may take a long time for such penetration.
For example, the transport of oxygen through a coating is typically
measured by exposing one side of the coating to oxygen, while nitrogen gas
sweeps the other side of the coating to an oxygen detector. The detector
measures the rate that oxygen comes through the coating. In order for the
detector to receive a measurable amount of oxygen, a large sample size is
utilized. Same approach is utilized for measurements of moisture
permeability of coatings, where a water vapor detector used instead.
Besides the disadvantage of requiring a large surface area, another
problem with this technique is the difficulty of mapping oxygen or/and
water vapor transport of different spatial regions of the single coating
or performing evaluation of multiple coatings with the same detection
system simultaneously.
Another disadvantage of typical barrier coating measurement techniques is
that the edges of the coating typically mischaracterize the measurement
results if the cross section of the analyzed barrier coating is small.
This "edge effect" provides another factor to account for in measuring and
analyzing new coating formulations, thereby reducing the efficiency of the
process.
Thus, there remains an unmet need to provide devices and methods for
efficiently measuring the barrier properties of a coating or combination
of coatings. There remains a further need to provide devices and methods
such that measurement errors associated with coating edge effects are
reduced or eliminated.
SUMMARY OF INVENTION
The present invention discloses methods and devices for measuring barrier
properties of coating arrays.
In one embodiment, a device for measurement of barrier properties of
barrier coatings includes a waveguide having an external surface with a
chemically sensitive layer disposed about the external surface of the
waveguide, where the chemically sensitive layer is responsive to a
material of interest. A predefined number of barrier coatings are
deposited onto the chemically sensitive layer, and each of the barrier
coatings has a corresponding barrier property with respect to the material
of interest. A light source is operable to propagate a wave within the
waveguide, and a detector is operable to measure impacts associated with
the propagated wave and associated with the respective barrier property of
each of the plurality of barrier coatings. A correlator correlates the
measured impact with a value of the barrier property for each of the
plurality of barrier coatings.
In another embodiment, a method for measuring barrier properties of coating
arrays includes applying a chemically sensitive layer to an exterior
surface of a waveguide, where the chemically sensitive layer has at least
one characteristic that changes in response to exposure to a material of
interest. Also, the method includes applying an array of barrier coatings
to the chemically sensitive layer, where each coating of the array of
barrier coatings has a barrier property with respect to the material of
interest. A wave is transmitted through the waveguide and the waveguide
with the applied array of barrier coatings is exposed to the material of
interest. The impact associated with the propagated wave is detected and
correlated with a value of a barrier property for each of the array of
barrier coatings.
Additional advantages and novel features of the invention will be set forth
in part in the description that follows, and in part will become more
apparent to those skilled in the art upon examination of the following or
upon learning by practice of the invention.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 presents a functional diagram of the various components of a
waveguide device in accordance with an embodiment of the present
invention;
FIG. 2 is a flow diagram of a method for measuring properties of coating
arrays in accordance with an embodiment of the present invention;
FIG. 3 presents a waveguide structure for measurements of barrier
properties of an array of coatings in accordance with an embodiment of the
present invention;
FIG. 4 shows an optical system for spatially resolved measurements of
barrier properties of an array of coatings toward a vapor of interest in
accordance with an embodiment of the present invention;
DETAILED DESCRIPTION
One embodiment of the present invention includes a system for evaluation of
barrier properties of coatings applied to the surface of a waveguide and
detected using optical time-of-flight (OTOF) information for a pulsed
light or other wave propagated via the waveguide. In an embodiment of the
present invention, one or more barrier coatings are applied onto the
surface of a dielectric waveguide, which may be of any geometry. In one
embodiment, the waveguide is preferably a cylindrical geometry. In these
embodiments, edge effects are eliminated, provided that a coating is
applied over the entire cross section of a waveguide, and provided that
the length of the coating is much longer than the coating thickness.
References will now be made in detail to embodiments of the present
invention, examples of which are illustrated in the accompanying drawings.
FIG. 1 presents a functional diagram of the various components of an
embodiment of the present invention for analyses using waveguides with
barrier coatings applied. As shown in FIG. 1, the waveguide having a
plurality of barrier coatings applied 1 is coupled to a light source 4
that transmits light to the waveguide 1. A detector 8 detects the
propagated light within the waveguide with the barrier coating applied 1.
And, in one embodiment, a separate display device 11 such as a personal
computer, digitizing oscilloscope or another type of display is coupled to
the detector 8 for displaying the detected light. With, for example, a
chemical, solvent, or other material of interest 6 exposed to the barrier
coated waveguide 1, an impact on or variation in the barrier coating that
affects the propagated light is detectable by the detector 8. Such
detection is then used to determine the barrier properties of the coatings
with improved precision. In an alternate embodiment, a similar set-up may
be utilized but with one of the plurality of barrier coatings applied to a
corresponding one of a plurality of waveguides each connected to the light
source, such that a single coating is deposited on each waveguide.
The principle of operation is as follows. When a pulse of light at probe
wavelength .lambda.1 is launched into a waveguide, analytical information
can be derived from the portion of light which is returned to the launch
end of the waveguide. The analytical signal might be the Rayleigh
backscatter at wavelength .lambda.1 or luminescence emission at a
different wavelength .lambda.2. The Rayleigh and luminescence signals are
modulated by variations in concentration of the material of interest at
the waveguide--sensing layer interface.
The Rayleigh scattering usually originates from microscopic inhomogeneities
in the waveguide material. These inhomogeneities cause spatial
fluctuations in the refractive index of the waveguide and generate
reflections of light guided in the waveguide. A portion of the scattered
light is recaptured by the waveguide numerical aperture in the reverse
direction.
In a device for measurements of barrier properties of coating arrays made
from a multimode dielectric waveguide and coated with a chemically
sensitive layer, detection of a material of interest transported through
the barrier coating can be based on Rayleigh backscatter. It can utilize
either variations in the refractive index or absorption coefficient of the
chemically sensitive layer on the waveguide. These variations modulate the
intensity of the backscatter signal because of losses in the evanescent
field. If the chemically sensitive layer on the waveguide is doped with a
fluorophore, the evanescent wave will excite the fluorophore at the
waveguide/sensing layer interface. Half of the luminescence emission
recaptured by the waveguide numerical aperture will be guided toward the
launch end of the waveguide. Alternatively, the wave resulting from the
interaction of the propagated wave and the coating/sensor combination may
be detected and its characteristics may be measured at the end of the
waveguide opposite the launching end.
To obtain information about the location of a material of interest, that
is, where a change in the back propagated radiation occurs (as measured
from the launch end of the waveguide), the level of the returned signal is
monitored as a function of the time delay between the launched and
returned light pulse. See, e.g., R. A. Potyrailo and G. M. Hieftje,
"Optical Time-of-Flight Chemical Detection: Spatially Resolved Analyte
Mapping with Extended-Length Continuous Chemically Modified Optical
Fibers," Anal. Chem. 70, 1453-1461 (1998) The relation between the
location/of interest along the waveguide and the time t required for the
light pulse to propagate forward and backward to this location is given
by:
t=l(n.sub.f +n.sub.b)/c, (1)
where c is the velocity of light in vacuum, and nf and nb are the
refractive indices of the waveguide at the wavelengths of the forward
(excitation wavelength) and backward (analytical wavelength) propagated
pulses.
To increase the signal level and to improve the signal-to-noise ratio
(S/N), repetitive light pulses should be used. However, only a single
pulse should propagate in the waveguide at a given time to avoid signal
overlap. Thus, the maximum pulse repetition rate Fmax is limited by the
length L of the waveguide and is given by
F.sub.max =c/(n.sub.f +n.sub.b)L. (2)
The returned signal in an OTOF measurement system was first formulated for
Rayleigh backscatter and then for Raman backscatter. If the relationship
is generalized also for luminescence detection, the backpropagated impulse
response from a distance/along the waveguide excited by a .delta.-pulse is
given by
P(l)=rP.sub.o S(l)exp{-.intg.[.alpha..sub.f (z)+.alpha..sub.b (z)]dz} (3)
where Po is the excitation power in the input pulse coupled into the
waveguide, r is the ratio of the transmitted to the reflected optical
power in the beamsplitter, S is a constant that depends on the local
numerical aperture (NA) of the waveguide, the luminescence quantum yield
of the immobilized fluorophore (in a luminescence-based sensor), or on the
Rayleigh and Raman scattering parameters of the waveguide (in a
scattering-based device ), and .alpha. f(z) and .alpha. b(z) are the
attenuation coefficients of the forward and backward traveling pulses,
respectively. In luminescence-based devices, both .alpha. f and .alpha. b
have two components, one each for the excitation and emission wavelengths.
The response of an OTOF device based on attenuation detection is a
convolution of the ideal impulse response described by eq 3 and the
temporal profile Rex(t) of the excitation pulse width .tau. ex. By using a
transformation of variables I.fwdarw.t given by eq 1, the response Patt(t)
of an attenuation-based OTOF device can be expressed as
P.sub.att (t)=P(t){character pullout}R.sub.ex (t), (4)
where {character pullout} denotes convolution. Similarly, the response
Pfl(t) of a luminescence-based OTOF device is given by
P.sub.fl (t)=P(t){character pullout}R.sub.ex (t){character pullout}R.sub.em
(t) (5)
where Rem(t) is the impulse response of the immobilized fluorophore (i.e.
an exponential decay having a time constant equal to the luminescence
lifetime .tau. em of the fluorophore).
In a device based on a statically quenched immobilized fluorophore, .tau.
em is constant. The output signal of such a device is a function of the
attenuation coefficient of the immobilized fluorophore. This functional
dependence is similar to that of an attenuation (absorption-based) device.
A device based on dynamic luminescence quenching of an immobilized
fluorophore does not exhibit a change in attenuation coefficient upon
exposure to a quencher. Rather, the luminescence lifetime .tau. em and
emission intensity I are a function of the quencher concentration [Q] as
described by the Stern-Volmer equation:
I.sub.o /I=.tau..sub.o.sub..sub.em /.tau..sub.em =1+K.sub.sv [Q] (6)
where Io and .tau. oem are the emission intensity and luminescence lifetime
of the fluorophore in the absence of the quencher and Ksv is the
Stern-Volmer quenching constant.
FIG. 2 is a flow diagram of a method for measuring barrier properties of
coating arrays in accordance with an embodiment of the present invention.
As shown in FIG. in an embodiment of the present invention, a sensor layer
such as a chemically sensitive layer is initially applied to a waveguide
(Block 21). The waveguide includes, for example, an optical fiber made of
quartz, a polymer, or other types of dielectric materials commonly used to
manufacture optical fibers. Such waveguides are available as optical
fibers of different diameters of fiber core, typically ranging from about
2 micron to about 2000 micron. The chemically sensitive layer is a
material that is responsive to exposure to a material of interest for
which a coating is designed to provide a barrier, and for which the
response is measurable by a detecting device. After coating with the
chemically sensitive layer, one or more barrier coatings are then applied
to the waveguide (Block 22). Materials for barrier coatings include, but
are not limited to, organic and inorganic materials, blends, composites,
and their combinations, oxides, nitrides and oxinitrides of silicon,
aluminum, zinc, boron and other metals, ceramics, polyvinyl alcohol,
ethylene vinyl alcohol copolymers, polyvinyl dichloride, different types
of nylon, cellophane, polyethylene terephtalate, PVC, PCTFE,
polypropylene, combinations thereof as well as other similar materials
typically used to provide a barrier to transport of a given material of
interest. Materials for barrier coatings are also those being developed
using combinatorial chemistry and high throughput screening approaches.
Further, the predetermined number of barrier coatings may include one
coating, or a plurality of different barrier coatings. A barrier coating
has a set of parameters that may be varied, the parameters including
composition, thickness, and coating preparation conditions such as
environment, method, curing, and other parameters. Each barrier coating on
the wave guide may have a small cross-section and length along the axis of
the waveguide. In general, the cross-section or thickness of each coating
may be in the range of about 0.1 nanometers to about 100 micrometers,
particularly in the range of about 1 nanometer to about 10 micrometers,
and more particularly in the range of about 10 nanometers to about 5
micrometers. The length along the waveguide of each barrier coating may be
in the range of about 1 millimeter to about 10 meters, particularly in the
range of about 5 millimeters to about 1 meter, and more particularly in
the range of about 1 centimeter to about 50 centimeters. The edge effects
which would normally provide inaccurate results are eliminated by
measuring the detected light within the waveguide.
Generally, an analysis is made of the barrier properties of each coating
such as susceptibility to penetration/transport or permeability to a
material of interest 6 to which the coatings 1 are exposed. After
initially applying the barrier coatings to the waveguide (Block 22), a
wave, such as a generated light pulse, is propagated within the waveguide
and the impact on the propagated wave is detected (Block 23). For example,
the wave has associated initial characteristics, such as frequency,
amplitude and phase, as it is forward-propagated within the waveguide. As
the wave interacts with a given coating/sensor combination, the initial
characteristics of the wave may be changed and this change can be detected
by measuring the associated back-propagated wave. Alternatively, as the
wave interacts with a given coating/sensor combination, the wave may cause
a response of another wave to be generated from the sensor layer, and this
new back-propagated wave is measured. The difference between the initial
characteristics of the forward-propagated wave and the characteristics of
the back-propagated wave is referred to as the impact on the wave. The
initial measurement establishes a baseline measurement and verifies the
initial state of each coating. The wave may be measured by, for example, a
photodetector coupled to an oscilliscope, or any other similar wave
measurement device.
Then, another wave is propagated in the waveguide while the waveguide is
exposed to the material of interest 6 (Block 24). For example, suitable
materials of interest 6 include oxygen gas, liquid water, moisture or
water vapor, organic and inorganic vapors, combinations thereof, and other
similar materials in any phase, but preferably as a liquid or gas. One or
more barrier coatings then becomes affected, such as through penetration
by or transport of the material of interest through the coating (Block
25).
As a result of the interaction between the material of interest 6 (FIG. 1)
with the chemically sensitive layer after transport of the material of
interest through one or more barrier coatings 1, the propagated wave
within the waveguide is impacted or the propagated wave causes a
measurable impact, i.e. fluorescence (Block 26). The impact on the wave is
defined as a measurable change in the wave, such as a variation in
amplitude, frequency, polarization state, phase and temporal properties of
the wave. The impact caused in the wave corresponds to and is correlated
with a measurable change of the characteristics of the respective barrier
coating. For example, the propagated wave may be affected by luminescence
in the chemically sensitive layer caused by transport of the material of
interest through the coating. The impact is determined relative to the
initial state of the coating by comparing the measured result of the
later-propagated with the measured result of the initially-propagated
wave. The impacts of the later-propagated wave are detected (Block 27) and
then correlated to a coating location (Block 28), and optionally displayed
on a display device (see FIG. 1), such as a monitor coupled to a processor
of a computer or on a display associated with the measurement device.
Further, the impact is correlated to an amount of a barrier characteristic
in such a way that the relative performance of each of the plurality of
barrier coatings may be analyzed and compared to determine relative
performance of each coating with respect to the material of interest.
Coatings 1 (FIG. 1) may be analyzed in this manner to measure a number of
barrier properties. Suitable barrier properties include permeability and
other similar barrier properties. Gas permeation properties of coatings
are typically characterized by: either the steady state gas permeation
rate, also called the transmission rate, defined as the volume of gas at
standard temperature and pressure passing through a unit area of the
coating per second divided by the pressure difference across the coating;
or the steady state gas permeability defined as the permeation rate times
the thickness of the coating. In the case of permeants (such as oxygen)
that do not strongly interact with the coating, the permeability is a
fundamental property of the coating, independent of coating thickness. In
this case it is called intrinsic permeability.
The composition of the chemically sensitive layer varies depending on the
particular barrier property and material of interest being analyzed.
Characteristics of the chemically sensitive layer, such as absorption
spectrum, refractive index, luminescence intensity, luminescence lifetime,
luminescence spectrum, etc. may change upon exposure to the material of
interest. The chemically sensitive layer is a film deposited onto the
waveguide and responsive to a material of interest. The chemically
sensitive layer can consist of an analyte-responsive material (such as
inorganic or organic material) and optionally a chemical reagent. Upon
exposure to the material of interest, the chemically sensitive layer is
affected by the material of interest.
The optical property of the layer upon material sorption can be changed by
the optical property of the material. For example, if a pure material
absorbs radiation at a certain wavelength, then the chemically sensitive
layer, after exposure to this material, will absorb radiation at the same
wavelength proportionally to the material concentration in contact to the
layer. If a pure material emits radiation at a certain wavelength, then
the chemically sensitive layer after exposure to this material will emit
radiation at the same wavelength proportionally to the material
concentration in contact to the layer. Other optical parameters that can
be altered upon contact with the analyte material are refractive index of
the layer and the amount of light scattered or diffused by the layer. If
the material does not possess the readily measurable optical property at a
given concentration, the chemical reagent is selected to be incorporated
into the layer. The chemical reagent changes its optical property
(typically UV-visible-IR absorption and/or luminescence spectra).
A sensor layer comprises at least one class of chemically sensitive
reagents. One class of reagents includes porphyrins. Examples of the
porphyrins include but are not limited to tetraphenylporphyrin, metal
porphyrins, such as platinum(II) octaethylporphyrin (Pt-OEP) and
palladium(II) octaethylporphyrin (Pd-OEP), and others as described in P.
Hartmann, W. Trettnak, "Effects of polymer matrices on calibration
functions of luminescent oxygen sensors based on porphyrin ketone
complexes," Anal. Chem. 1996, 68, 2615-2620; A. Mills, A. Lepre,
"Controlling the response characteristics of luminescent porphyrin plastic
film sensors for oxygen," Anal. Chem. 1997, 69, 4653-4659; Potyrailo, R.
A.; Hieftje, G. M., Oxygen detection by fluorescence quenching of
tetraphenylporphyrin immobilized in the original cladding of an optical
fiber, Anal. Chim. Acta 1998, 370, 1-8.
Another class of reagents includes polycyclic aromatic hydrocarbons.
Examples and applications of this class of fluorophores are described by:
I. B. Berlman, Handbook of luminescence spectra of aromatic molecules,
Academic Press, New York, N.Y., 1971; O. S. Wolfbeis, Fiber Optic Chemical
Sensors and Biosensors; O. S. Wolfbeis, Ed.; CRC Press: Boca Raton, Fla.,
1991; Vol. 2; pp 19-53; Hobbs, S. E.; Potyrailo, R. A.; Hieftje, G. M.,
Scintillator light source for chemical sensing in the near-ultraviolet,
Anal. Chem. 1997, 69, 3375-3379. Preferred fluorophores of this class
include pyrene, pyrenebutyric acid, fluoranthene, decacyclene,
diphenylanthracene, and benzo(g,h,l)perylene.
Another class of reagents includes a variety of long-wave absorbing dyes
such as perylene dibutyrate, and heterocycles including fluorescent
yellow, trypaflavin and other heterocycle compounds as described by: O. S.
Wolfbeis, Fiber Optic Chemical Sensors and Biosensors; O. S. Wolfbeis,
Ed.; CRC Press: Boca Raton, Fla., 1991; Vol. 2; pp 19-53.
Yet another group of reagents includes metal-organic complexes of
ruthenium, osmium, iridium, gold and platinum as described by: O. S.
Wolfbeis, Fiber Optic Chemical Sensors and Biosensors; O. S. Wolfbeis,
Ed.; CRC Press: Boca Raton, Fla., 1991; Vol. 2; pp 19-53, J. N. Demas, B.
A. Degraff, P. B. Coleman, "Oxygen sensors based on luminescence
quenching," Anal. Chem. 1999, 71, 793A-800A;J. N. Demas, B. A. DeGraff,
"Design and applications of highly luminescent transition metal
complexes," Anal. Chem. 1991, 63, 829A-837A; A. Mills, A. Lepre, B. R.
Theobald, E. Slade, B. A. Murrer, "Use of luminescent gold compounds in
the design of thin-film oxygen sensors," Anal. Chem. 1997, 69, 2842-2847;
Potyrailo, R. A.; Hieftje, G. M., Use of the original silicone cladding of
an optical fiber as a reagent-immobilization medium for intrinsic chemical
sensors, Fresenius' J. Anal. Chem. 1999, 364, 32-40.
Yet another group of reagents includes solvatochromic dyes as extensively
reviewed in, for example, C. Reichardt, Chemical Reviews, volume 94, pages
2319-2358 (1994). Preferred fluorescent solvatochromic dyes have a
luminescence quantum yield of greater than about 0.01. Other
characteristics of the dyes include positive and negative solvatochromism
which corresponds to the bathochromic and hypsochromic shifts,
respectively of the emission band with increasing solvent polarity. In
addition to the solvent-induced spectral shifts of the emission spectra,
some dyes exhibit the solvent-dependent ratio of emission intensities of
two luminescence bands. One such solvatochromic dye is pyrene. Some
examples of preferred solvatochromic dyes include
4-dicyanmethylene-2-methyl-6-(p-dimethylaminostyryl)-4 H-pyran (DCM; CAS
Registry No. 51325-91-8); 6-propionyl-2-(dimethylamino)naphthalene
(PRODAN; CAS Registry No. 70504-01-7);
9-(diethylamino)-5H-benzo[a]phenoxazin-5-one (Nile Red; CAS Registry No.
7385-67-3); phenol blue; stilbazolium dyes; coumarin dyes; ketocyanine
dyes, including CAS Registry No. 63285-01-8; Reichardt's dyes including
Reichardt's betaine dye
(2,6-diphenyl-4-(2,4,6-triphenylpyridinio)phenolate; CAS Registry No.
10081-39-7); merocyanine dyes, including merocyanine 540 (CAS Registry No.
62796-23-0); so-called .pi. * dyes, including N,N-dimethyl-4-nitroaniline
(NDMNA; CAS Registry No.100-23-2) and N-methyl-2-nitroaniline (NM2NA; CAS
Registry No.612-28-2); and the like. Applications of solvatochromic dyes
for monitoring of moisture are described for example in Sadaoka, Y.;
Matsuguchi, M.; Sakai, Y.; Murata, Y.-U., Optical humidity sensor using
Reichardt's betain dye-polymer composites, Chem. Lett 1992, 53-56;
Sadaoka, Y.; Sakai, Y.; Murata, Y., Optical humidity and ammonia gas
sensors using Reichardt's dye-polymer composites, Talanta 1992, 39,
1675-1679; Potyrailo, R. A.; Hieftje, G. M., Use of the original silicone
cladding of an optical fiber as a reagent-immobilization medium for
intrinsic chemical sensors, Fresenius' J. Anal. Chem. 1999, 364, 32-40.
Yet another group of reagents includes colorimetric and luminescent
acid-base and cationic reagents as extensively reviewed in, for example,
Kolthoff, I. M. Acid-Base Indicators; The MacMillan Company: New York,
1937; Bacci, M.; Baldini, F.; Bracci, S., Spectroscopic behavior of
acid-base indicators after immobilization on glass supports, Appl.
Spectrosc. 1991, 45, 1508-1515; Sadaoka, Y.; Matsuguchi, M.; Sakai, Y.;
Murata, Y.-U., Optical humidity sensing characteristics of Nafion-dyes
composite thin films, Sens. Actuators B 1992, 7, 443-446; Sadaoka, Y.;
Sakai, Y.; Murata, Y., Optical properties of cresyl violet-polymer
composites for quantification of humidity and ammonia gas in ambient air,
J. Mater. Chem. 1993, 3, 247-251; Zinger, B.; Shier, P., Spectroscopic
studies of cationic dyes in Nafion, Preliminary investigation of a new
sensor for hydrophilic contamination in organic solvents, Sens. Actuators
B 1999, 56, 206-214; Haugland, R. P. Handbook of Fluorescent Probes and
Research Chemicals; Molecular Probes: Eugene, Oreg., 1996. Some of these
dyes are thymol blue, congo red, methyl orange, bromocresol green, methyl
red, bromocresol purple, bromothymol blue, cresol red, phenolphthalein,
SNAFL indicators, SNARF indicators, 8-hydroxypyrene-1,3,6-trisulfonic
acid, fluorescein and its derivatives, oregon green, and a variety of dyes
mostly used as laser dyes including rhodamine dyes, styryl dyes, cyanine
dyes, and a large variety of other dyes. These reagents may also be
referred to as pH reagents. Yet another group of reagents includes
oxygen-sensitive colorimetric reagents. Some reagents useful for
colorimetric determinations of molecular oxygen are reviewed in Chemical
Detection of Gaseous Pollutants; Ruch, W. E., Ed.; Ann Arbor Science
Publishers: Ann Arbor, Mich., 1968. These include, among others,
2,4-diaminophenol dihydrochloride, manganous oxide, combination of
manganous hydroxide and potassium iodide containing starch, ferrous salt
in combination with methylene blue, reduced form of sodium
anthraquinone-B-sulfonate, reduced form of ammonium
anthraquinone-2-sulfonate, carbohydrate of Tschitschibabin, alkaline
pyrogallol, and ammoniacal cuprous chloride. These and many other
colorimetric reagents can be dispersed in a solid matrix, such as sol-gel,
silica-gel and/or a polymer film, or dissolved in a suitable solvent.
Variation of the detectable property of a chemically sensitive film can be
performed upon a change of refractive index of the film upon exposure to
the material of interest, such as water vapor. Such moisture sensitive
material can be a hydrogel. A hydrogel is a three dimensional network of
hydrophilic polymers which have been tied together to form water-swellable
but water insoluble structures. The term hydrogel is to be applied to
hydrophilic polymers in a dry state (xerogel) as well as in a wet state as
described in U.S. Pat. No. 5,744,794.
There are a number of methods that may be used to tie these hydrogels
together. First, tying via radiation or radical cross-linking of
hydrophilic polymers, examples being poly(acrylic acids), poly(methacrylic
acids), poly (hydroxyethylmethacrylates), poly(glyceryl methacrylate),
poly(vinyl alcohols), poly (ethylene oxides), poly(acrylamides),
poly(N-acrylamides), poly(N,N-dimethylaminopropyl-N'-acrylamide),
poly(ethylene imines), sodium/potassium poly(acrylates), polysacharides
e.g. xanthates, alginates, guar gum, agarose etc., poly(vinyl pyrrolidone)
and cellulose based derivatives. Second, tying via chemical cross-linking
of hydrophilic polymers and monomers, with appropriate polyfunctional
monomers, examples include poly(hydroxyethylmethacrylate) cross-linked
with suitable agents, the copolymerisation of hydroxyethylmethacrylate
monomer with dimethacrylate ester crosslinking agents, poly(ethylene
oxide) based polyurethanes prepared through the reaction of
hydroxyl-terminated poly (ethylene glycols) with polyisocyanates or by the
reaction with diisocyanates in the presence of polyfunctional monomers
such as triols, and cellulose derivates cross-linked with dialdehydes,
diepoxides and polybasic acids. Third, tying via incorporation of
hydrophilic monomers and polymers into block and graft copolymers,
examples being block and graft copolymers of poly(ethylene oxide) with
suitable polymers, poly(vinyl pyrrolidone)-co-polystyrene copolymers,
polyurethanes and polyurethaneureas and polyurethaneureas based on poly
(ethylene oxide), polyurethaneureas and
poly(acrylonitrile)-co-poly(acrylic acid) copolymers, and a variety of
derivatives of poly(acrylontriles), poly(vinyl alcohols) and poly(acrylic
acids). Fourthly molecular complex formation between hydrophilic polymers
and other polymers, examples being poly(ethylene oxides) hydrogel
complexes with poly(acrylic acids) and poly(methacrylic acids). Last,
tying via entanglement cross-linking of high molecular weight hydrophilic
polymers, examples being hydrogels based on high molecular weight
poly(ethylene oxides) admixed with polyfunctional acrylic or vinyl
monomers.
Examples of applications of these materials are in Michie, W. C., Culshaw,
B., Konstantaki, M.; McKenzie, I., Kelly, S., Graham, N. B., Moran, C.,
Distributed pH and water detection using fiber-optic sensors and
hydrogels, J. Lightwave Technol. 1995, 13, 1415-1420; Bownass, D. C.;
Barton, J. S.; Jones, J. D. C., Serially multiplexed point sensor for the
detection of high humidity in passive optical networks, Opt. Lett. 1997,
22, 346-348; Michie, W. C.; Graham, N. B.; Cuishaw, B.; Gardiner, P. T.;
Moran, C., Apparatus for detecting aqueous environments, U.S. Pat. No.
5,744,794 (1995).
Chemically sensitive reagents are incorporated into a sensor layer formed
from film-forming polymeric and/or inorganic material. The material for
the sensor layer may affect the detection properties such as selectivity,
sensitivity, and limit of detection. Thus, suitable material for the
sensor layer is selected from polymeric and/or inorganic material capable
of providing required response time, material of interest permeability,
material of interest solubility, degree of transparency and hardness, and
other similar characteristics relevant to the material of interest and the
desired barrier property to be analyzed.
In general, the sensor layer has a response time in the range of about 1
microsecond 60 minutes, particularly in the range of about 1 millisecond
10 minutes, and more particularly in the range of about 1 second 1 minute.
In general, the permeability of the barrier coating to material of interest
is in the range of about 0.0001 100 cm.sup.3 mm/m.sup.2 day atm,
particularly in the range of about 0.001 10 cm.sup.3 mm/m.sup.2 day atm,
and more particularly in the range of about 0.005 5 cm.sup.3 mm/m.sup.2
day atm.
In general, the sensor layer has a thickness in the range of about 0.001
micrometer 1000 micrometers, particularly from about 0.01 micrometer 500
micrometers, and more particularly in the range of about 0.1 micrometer
200 micrometers.
For example, in general polymers that can be used as matrices for oxygen,
water vapor, and other sensors can be divided into several classes as
described by: S. A. Stern, B. Krishnakumar, S. M. Nadakatti, Physical
Properties of Polymers Handbook; J. E. Mark, Ed.; AIP Press: New York,
1996; pp 687-700. Such classes include polyolefins, vinyl and vinylidene
polymers, natural and synthetic rubbers, polyesters, polycarbonates,
cellulose derivatives, fluoropolymers, polyorganosiloxanes, polynitriles,
polyamides, polyimides, polyurethanes, polyoxides, polysulfones,
polyacetylenes, polyacrylics.
More detailed examples of polymers are described by Freud, M. S.; Lewis, N.
S., "A chemically diverse conducting polymer-based "electronic nose"",
Proc. Natl. Acad. Sci. USA 1995, 92, 2652-2656; Albert, K. J.; Lewis, N.
S.; Schauer, C. L.; Sotzing, G. A.; Stitzel, S. E.; Vaid, T. P.; Walt, D.
R., "Cross-reactive chemical sensor arrays,"Chem. Rev. 2000, 1000,
2595-2626; Grate, J. W.; Abraham, H.; McGill, R. A. In "Handbook of
Biosensors and Electronic Noses. Medicine, Food, and the Environment" E.
Kress-Rogers, Ed.; CRC Press: Boca Raton, Fla., 1997; pp 593-612; Grate,
J. W.; Abraham, M. H., "Solubility interactions and the design of
chemically selective sorbent coatings for chemical sensors and arrays,"
Sens. Actuators B 1991, 3, 85-111; U.S. Pat. Nos. 6,010,616 and 6,093,308.
They include: conducting polymers such as poly(anilines), poly(thiophenes),
poly(pyrroles), poly(acetylenes), etc.; main-chain carbon polymers such as
poly (dienes), poly(alkenes), poly(acrylics), poly(methacrylics),
poly(vinyl ethers), poly (vinyl thioethers), poly(vinyl alcohols),
poly(vinyl ketones), poly(vinyl halides), poly (vinyl nitriles),
poly(vinyl esters), poly(styrenes), poly(arylenes), etc.; main-chain
acyclic heteroatom polymers such as poly(oxides), poly(carbonates),
poly(esters), poly(anhydrides), poly(urethanes), poly(sulfonates),
poly(siloxanes), poly(sulfides), poly(thioesters), poly(sulfones),
poly(sulfonamides), poly(amides), poly(ureas), poly (phosphazenes),
poly(silanes), poly(silazanes), etc.; and, main-chain heterocyclic
polymers such as poly(benzoxazoles), poly(oxadiazoles), poly
(benzothiazinophenothiazines), poly(benzothiazoles),
poly(pyrazinoquinoxalines), poly(pyromellitimides), poly(quinoxalines),
poly(benzimidazoles), poly(oxindoles), poly(oxoisoindolines),
poly(dioxoisoindolines), poly(triazines), poly(pyridazines),
poly(piperazines), poly(pyridines), poly(piperidines), poly(triazoles),
poly (pyrazoles), poly(pyrrolidines), poly(carboranes),
poly(oxabicyclononanes), poly (dibenzofurans), poly(phthalides),
poly(acetals), poly(anhydrides), carbohydrates, etc.
Other types of matrices include: the copolymers, polymer blends, and
physical mixtures or polymers with additives such as organic and inorganic
pigments, conducting, semiconducting, and non-conducting particles;
inorganic sol-gel materials produced by condensation reactions, these
materials can be doped with organic components; and polyelectrolytes, such
as high-density polyethylene grafted with poly(styrenesulfonic acid),
Nafion, and others.
The chemically sensitive layer is formed by incorporating the chemically
sensitive reagents into the polymeric and/or inorganic material for the
sensor layer. Incorporation of the chemically sensitive reagents may be
carried out by dissolving a chemically sensitive reagent in a solution or
suspension of polymeric and/or inorganic material in a suitable solvent
and then the resultant solution or suspension is applied to a substrate to
form a chemically sensitive layer using various methods using thin-film
deposition techniques that are explained below. An optional step is curing
or condensation reaction. Solvents can be either polar or non polar,
including but not limited to water, ethanol, methanol, acetone,
chloroform, toluene, benzene, and hexane.
Another method for incorporation of chemically sensitive reagents includes
dissolving a chemically sensitive reagent in a suitable solvent and
immersing a polymer or/and inorganic film into the reagent solution. The
solvent is sorbed into or onto the film and some of the chemically
sensitive reagent molecules become trapped in the film. Upon drying,
curing, or condensation, the solvent is removed while the chemically
sensitive reagent remains trapped in the film. Covalent attachment of the
reagent to the film is also possible.
For example, for oxygen permeability, a suitable chemically sensitive layer
includes a polymeric material, such as polyvinyl chloride (PVC),
polystyrene (PS), polycarbonate (PC), poly(methyl methacrylate) (PMMA),
PMMA/CAB blends, poly(1-trimethylsilyl-1-propyne), fluoro-polymer such as
poly(styrene-co-trifluoroethyl-methacrylate) (poly-styrene-co-TFEM) and
other fluoropolymers, sol-gels doped with an oxygen sensitive reagent,
such as platinum or palladium porphyrins, such as platinum(II)
octaethylporphyrin (Pt-OEP) and palladium(II) octaethylporphyrin (Pd-OEP);
metal-organic complexes of ruthenium, osmium, iridium, gold and platinum;
or other known similar materials.
Other suitable example of chemically sensitive layers include polycyclic
aromatic hydrocarbons such as pyrene, pyrenebutyric acid, fluoranthene,
decacyclene, diphenylanthracene, and benzo(g,h,l)perylene, immobilized in
a cellulose acetate butyrate (CAB), silicones, silicone blends, silicone
copolymers, combinations thereof, and other similar materials.
Still other suitable example of chemically sensitive layers include
solvatochromic, acid-base, and cationic dyes such as pyrene,
4-dicyanmethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran;
6-propionyl-2-(dimethylamino) naphthalene;
9-(diethylamino)-5H-benzo[a]phenoxazin-5-one; phenol blue; stilbazolium
dyes; coumarin dyes; ketocyanine dyes, Reichardt's dyes; merocyanine dyes,
thymol blue, congo red, methyl orange, bromocresol green, methyl red,
bromocresol purple, bromothymol blue, cresol red, phenolphthalein, SNAFL
dyes, SNARF dyes, 8-hydroxypyrene-1,3,6-trisulfonic acid, fluorescein and
its derivatives, oregon green, and a variety of dyes mostly used as laser
dyes including rhodamine dyes, styryl dyes, cyanine dyes, and a large
variety of other dyes immobilized in an inorganic material such as sol-gel
matrix or in a polymeric material, such as polyvinyl chloride (PVC),
polystyrene (PS), polycarbonate (PC), poly (methyl methacrylate) (PMMA),
PMMA/CAB blends, fluoro-polymer such as poly
(styrene-co-trifluoroethyl-methacrylate) (poly-styrene-co-TFEM) and other
fluoropolymers, cation exchange membranes such as Nafion, and others,
combinations thereof, and other similar materials.
For example, the sensor layer may be exposed to varying concentrations of
oxygen, water vapor, other inorganic and organic vapors and gases and
their combinations at different ratios. For example, in measurements of
oxygen barrier property, oxygen concentrations range from 0 to 100% by
volume. Partial pressure of oxygen can range from 0 to 1 atmosphere.
However, in order to accelerate penetration of oxygen, the partial
pressure can be increased higher than 1 atmosphere and, depending on the
equipment used, can be, for example 10 or 100 atmosphere or even higher.
In measurements of moisture barrier property, water vapor concentrations
range from 0 to 100 % by volume. Partial pressure of water vapor can range
from 0 to 1 atmosphere. However, in order to accelerate penetration of
water vapor, the partial pressure can be increased higher than 1
atmosphere and, depending on the equipment used, can be, for example 10 or
100 atmosphere or even higher.
The sensor layer may be exposed first to the atmosphere at which the
coating deposition was performed, and then to nitrogen, oxygen, water
vapor, or other inorganic or organic vapor or gas or their combinations at
different ratios.
The change in the absorbance, refractive index, luminescence intensity, or
lifetime of the regions of the sensor materials may be measured using a
described system.
In one embodiment, the correlation of detection to impacted barrier
coatings is determined via use of optical time-of-flight chemical
detection (OTOF), otherwise known as spatially resolved mapping. Upon
measurements of back-reflected light, this technique is known as optical
time domain reflectometry (OTDR). With this technique, a pulse of light is
periodically launched into the waveguide, and analytical information is
derived from the amplitude and/or other characteristics of the returned
portion of the light. In one embodiment, the amplitude of the returned
light is modulated by variations in analyte concentration along the
waveguide that occur due to penetration of a material of interest through
a barrier coating applied to the waveguide. In particular, in one
embodiment, information about the location of the variation in analyte
concentration is obtained from the measured time delay between the
launched and returned pulses of light.
To address drawbacks with this technique when absorbance of material of
interest is detected in the UV-IR spectral ranges or when chemically
sensitive colorimetric dyes are used with the basic OTOF sensing of this
method, including low levels of detected backscatter signal, an embodiment
of the present invention also includes use of absorption-modulated
luminescence detection which raises signal levels of absorption-based
sensors to levels found in luminescence-based sensors. With this approach,
the luminescence intensity of an immobilized analyte-insensitive
fluorophore is monitored by an analyte sensitive indicator as a function
of absorbance caused by a second immobilized analyte-insensitive
fluorophore.
Another potential drawback relating to OTOF sensing using detection of
absorbance of material of interest in the UV-IR spectral ranges or using
chemically sensitive colorimetric dyes and/or statically quenched
fluorophores is the accumulative analyte-induced light attenuation. A
local increase in evanescent-wave absorbance by an immobilized reagent or
absorbance of the material of interest in the UV-IR spectral ranges leads
to a drop in light intensity available for propagation farther down the
waveguide. The dynamic range can therefore be limited by high analyte
concentrations along the waveguide. To address this limitation,
dynamically quenched fluorophores are used with sensing. Sensors based on
immobilized dynamically quenched fluorophores do not exhibit a change in
attenuation coefficient upon exposure to a quencher. See, e.g., R. A.
Potyrailo and G. M. Hieftge, "Spatially Resolved Analyte Mapping With
Time-Of-Flight Optical Sensors," Trends. Anal. Chem., vol. 17, 593-604
(1998).
The chemically sensitive layer and the barrier coatings are deposited on
the waveguide using a number of methods and systems, such as by spraying,
drawing, dipping and otherwise depositing the materials on the waveguide.
A length of waveguide material is coatable with a chemically sensitive
layer, and the chemically sensitive layer is then coatable with adjacent
layers of barrier coatings, such that an array of barrier coatings is
formed upon the length of the waveguide material.
Thin-film deposition techniques in combination with physical masking
techniques or photolithographic techniques can be used to apply a barrier
coating layer onto a sensor layer. Such thin-film deposition techniques
can generally be broken down into the following four categories:
evaporative methods, glow discharge processes, gas-phase chemical
processes, and liquid-phase chemical techniques. Included within these
categories are, for example, sputtering techniques, spraying techniques,
laser ablation techniques, electron beam or thermal evaporation
techniques, ion implantation or doping techniques, chemical vapor
deposition techniques, as well as other techniques used in the fabrication
of integrated circuits. All of these techniques can be applied to deposit
highly uniform layers, i.e., thin-films, of the various coating materials
on selected regions on the sensor layer. Moreover, by adjusting the
relative geometries of the masks, the delivery source and/or the
substrate, such thin-film deposition techniques can be used to generate
uniform gradients at each reaction region on the substrate or,
alternatively, over all of the reaction regions on the substrate. For an
overview of the various thin-film deposition techniques which can be used
in the methods of the present invention, see, for example, Ballantine, D.
S., Jr.; White, R. M.; Martin, S. J.; Ricco, A. J.; Frye, G. C.; Zellers,
E. T.; Wohltjen, H. "Acoustic Wave Sensors: Theory, Design, and
Physico-Chemical Applications", Chapter 6, Academic Press: San Diego,
Calif., 1997; which are incorporated herein by reference for all purposes.
In one embodiment, thin-films of the various barrier coating materials can
be deposited onto the sensor layer using evaporative methods in
combination with physical masking techniques. Generally, in thermal
evaporation or vacuum evaporation methods, the following sequential steps
take place: (1) a vapor is generated by boiling or subliming a target
material; (2) the vapor is transported from the source to a substrate; and
(3) the vapor is condensed to a solid film on the substrate surface.
Evaporants, i.e., target materials, which can be used in the evaporative
methods cover an extraordinary range of chemical reactivities and vapor
pressures and, thus, a wide vary of sources can be used to vaporize the
target materials. Such sources include, for example, resistance-heated
filaments, electron beams; crucible heated by conduction, radiation or
rf-inductions; and arcs, exploding wires and lasers. In preferred
embodiments of the present invention, thin-film deposition using
evaporative methods is carried out using lasers, filaments, electron beams
or ion beams as the source. Successive rounds of deposition, through
different physical masks, using evaporative methods can be used to
generate a library or array of barrier coatings on a sensory layer for
detection of defects in the barrier coatings in combinatorial discovery of
coating materials.
Molecular Beam Epitaxy (MBE) is an evaporative method that can be used to
grow epitaxial thin-films. In this method, the films are formed on
single-crystal substrates by slowly evaporating the elemental or molecular
constituents of the film from separate Knudsen effusion source cells (deep
crucibles in furnaces with cooled shrouds) onto substrates held at
temperatures appropriate for chemical reaction, epitaxy and re-evaporation
of excess reactants. The Knudsen effusion source cells produce atomic or
molecular beams of relatively small diameter which are directed at the
heated substrate, usually silicon or gallium arsenide. Fast shutters are
interposed between the source cells and the substrates. By controlling
these shutters, one can grow superlattices with precisely controlled
uniformity, lattice match, composition, dopant concentrations, thickness
and interfaces down to the level of atomic layers.
In addition to evaporative methods, thin-films of the various barrier
coating materials can be deposited onto the sensor layer or onto the
substrate using glow-discharge processes in combination with physical
masking techniques. The most basic and well known of these processes is
sputtering, i.e., the ejection of surface atoms from an electrode surface
by momentum transfer from bombarding ions to surface atoms. Sputtering or
sputter-deposition is a term used by those of skill in the art to cover a
variety of processes, all of which can be used in the methods of the
present invention. One such process is RF/DC Glow Discharge Plasma
Sputtering. In this process, a plasma of energized ions is created by
applying a high RF or DC voltage between a cathode and an anode. The
energy ions from the plasma bombard the target and eject atoms which are
then deposited on a substrate, a sensor layer. Ion-Beam Sputtering is
another example of a sputtering process which can be used to deposit
thin-films of the various barrier coating materials on a substrate.
Ion-Beam Sputtering is similar to the foregoing process except the ions
are supplied by an ion source and not a plasma. It will be apparent to one
of skill in the art that other sputtering techniques (e.g., diode
sputtering, reactive sputtering, etc.) and other glow-discharge processes
can be used in the methods of the present invention to deposit thin-films
on a substrate and a sensor layer. Successive rounds of deposition,
through different physical masks, using sputtering or other glow-discharge
techniques, can be used to generate an array or library of barrier
coatings on a sensor layer for detection of defects in the barrier coating
for use of combinatorial discovery of coating materials.
In addition to evaporative methods and sputtering techniques, thin-films of
the various barrier coating materials can be deposited onto the sensor
layer or onto the substrate using Chemical Vapor Deposition (CVD)
techniques in combination with physical masking techniques. CVD involves
the formation of stable solids by decomposition of gaseous chemicals using
heat, plasma, ultraviolet, or other energy source, or a combination of
energy sources. Photo-Enhanced CVD, based on activation of the reactants
in the gas or vapor phase by electromagnetic radiation, usually short-wave
ultraviolet radiation, and Plasma-Enhanced CVD, based on activation of the
reactants in the gas or vapor phase using a plasma, are two particularly
useful chemical vapor deposition techniques. Successive rounds of
deposition, through different physical masks, using CVD technique can be
used to generate an array or library of barrier coatings on a sensor layer
for detection of defects in the barrier coating in combinatorial discovery
of coating materials.
In addition to evaporative methods, sputtering and CVD, thin-films of the
various reactants can be deposited onto the sensor layer or onto the
substrate using a number of different mechanical techniques in combination
with physical masking techniques. Such mechanical techniques include, for
example, spraying, spinning, dipping, draining, flow coating, roller
coating, pressure-curtain coating, brushing, etc. Of these, the spray-on
and spin-on techniques are particularly useful. Sprayers which can be used
to deposit thin-films include, for example, ultrasonic nozzle sprayers,
air atomizing nozzle sprayers and atomizing nozzle sprayer. In ultrasonic
sprayers, disc-shaped ceramic piezoelectric transducers covert electrical
energy into mechanical energy. The transducers receive electrical input in
the form of a high-frequency signal from a power supply that acts as a
combination oscillator/amplifier. In air atomizing sprayers, the nozzles
intermix air and liquid streams to produce a completely atomized spray. In
atomizing sprayers, the nozzles use the energy from a pressurized liquid
to atomize the liquid and, in turn, produce a spray. Successive rounds of
deposition, through different physical masks, using mechanical techniques,
such as spraying, can be used to generate an array or library of barrier
coatings on a circular sensor layer for detection of transport properties
of barrier coatings in combinatorial discovery of coating materials.
The barrier coating suitably has a thickness from 0.1 nm to 100
micrometers, particularly from 1 nm to 10 micrometers, and more
particularly from 10 nm to 5 micrometers.
In combinatorial discovery of coating materials for applications as barrier
and other types of coatings, the rapid evaluation of permeability of
coatings is needed. To provide methods and devices for measurements of
barrier properties of multiple coatings with the reduced errors associated
with the edge effects, in an embodiment of the present invention, an array
of barrier coatings is deposited onto the waveguide structure, as shown in
FIG. 3. FIG. 3 presents a waveguide 30 having an outer side surface coated
with a chemically sensitive layer 31 and an array of barrier coatings 32,
33, 34, 35, 36, 37, 38, 39. Preferably, each of the elements of the array
of barrier coatings has a known predetermined different composition such
that the measured variations in barrier coating performance may be
correlated to the known variations in the coating composition. The array
of barrier coatings are adjacently positioned lengthwise along the
waveguide such that there is no space between the coatings, thereby
eliminating edge effects in all three dimensions. For example, the barrier
coatings may include a single coating having a varying composition
lengthwise along the waveguide. Such a barrier coating may be formed, for
example, by simultaneously depositing different combinations of different
materials lengthwise along the waveguide, where a given material
composition forming a barrier coating is mappable to a given position.
Alternatively, if there is space between the array of coatings, then the
edge effects are eliminated in two dimensions. An array of barrier coating
may also include situations when coating thickness is introduced as a
variable parameter. An array of barrier coating may also include
situations when processing and reaction conditions of coating fabrication
are introduced as variable parameters.
FIG. 4 shows one embodiment of an optical system 40 for spatially resolved
measurements of barrier properties of an array of coatings 46 with regard
to a material of interest 6. The system 40 performs the measurements
utilizing the spatially resolved capability provided by an optical
time-of-flight detection technique. FIG. 4 presents a light source 41 that
pulses a wave of light through an optical fiber input 42 and a fiber optic
coupler 43 into a chemically sensitive waveguide 44. Waveguide 44 has a
structure similar to that of waveguide 30 (see FIG. 3), including a
chemically sensitive layer and an array of barrier coatings 46. Although
shown as spaced apart along the length of the waveguide 44, the array of
barrier coatings 46 may be positioned without any space in between each
coating to eliminate edge effects in two or three dimensions. The array of
barrier coatings 46 is exposed to one or more material(s) of interest 6
contained within a gas cell 45. A detector 47, such as a photodetector for
measuring the pulsed light wave, is connected to the waveguide 44 to
measure the effects on each barrier coating to the exposure to the
material of interest 6. The system 40 may also include a display 48
connected to the detector 47 for graphically depicting the measurements of
the detector. The display includes, for example, a personal computer (PC),
a microcomputer, a minicomputer, a mainframe computer, or other device
having a processor.
For example, the light source 41 may include a pulsed laser, or other
suitable wave source such as those listed in the following Table 1.
TABLE 1
Useful Light/Wave Sources
Source Spectral range of emission (nm)
Diode lasers different diode lasers cover ranges from 400 to 1500
nm
Light emitting different diodes cover ranges from 370 to 1500
diodes
Excimer lasers 157, 193, 248, 308, 351
Nitrogen laser 337
Nd: YAG laser fundamental-1064, frequency doubled-532,
tripled-355, quadrupled-266
Ti: Sapphire laser 72-1000, frequency doubled 360-500
Dye lasers 360-990, frequency doubled 235 to 345
In an embodiment of the present invention, the waveguide includes, for
example, a chemically sensitive layer of an oxygen sensitive material if
oxygen barrier properties are of interest.
In another embodiment of the present invention, the waveguide includes a
chemically sensitive layer of a moisture sensitive material if moisture
barrier properties are of interest.
In an embodiment of the present invention, the waveguide includes, for
example, a chemically sensitive layer of an oxygen and moisture sensitive
material if combined oxygen and moisture barrier properties are of
interest.
Other fluids, gases, vapors, or liquids are measurable by incorporating
other chemical reagents into the material ofthe chemically sensitive
layer.
The waveguide is preferably impermeable to the material of interest.
Examples of waveguides of such geometry, known as optical fibers, are
shown in Table 2.
TABLE 2
Useful optical fiber waveguides
Fiber cladding
Fiber core material (and materials (and
Supplier diameters, microns) diameters, microns)
Polymicro silica (125, 200, 400, 500, hard polymer (140,
Technologies, Inc., 700) 220, 420, 520, 740)
Phoenix, Az silica (300, 400, 600, 800) silicone (450, 500,
700, 900)
Fiberguide silica (200, 300, 400, 600, silicone (300, 400,
Industries, Inc., 800, 1000, 1500, 2000) 500, 700, 900, 1100,
Stirling, NJ 1650, 2150)
3M Specialty silica (125, 200, 300, 400, hard polymer (140,
Fibers, West 600, 800, 1000, 1500) 230, 330, 430,
Haven, CT silica (200, 400, 600, 1000) 630, 830, 1035, 1550)
silicone (380, 600,
830, 1400)
The original fiber cladding can be chemically modified with a chemically
sensitive reagent of interest as described by Potyrailo, R. A.; Hieftje,
G. M., "Use of the original silicone cladding of an optical fiber as a
reagent-immobilization medium for intrinsic chemical sensors," Fresenius'
J. Anal. Chem. 1999, 364, 32-40. Also, the fiber cladding can be removed
using methods described in a Product Catalog "3M Power-Core Fiber
Products" from Specialty Fibers, West Haven, Conn. and in Ruddy, V.;
MacCraith, B. D.; Murphy, J. A., "Evanescent wave absorption spectroscopy
using multimode fibers," J. Appl. Phys. 1990, 67, 6070-6074, where
cladding materials can be removed by applying available solvents.
The chemically sensitive material (reagent in a suitable matrix) can be
deposited as described above.
For detection of the wave back-propagating in the waveguide, several
possible detection system configurations can be used. In one detection
system, light from a pulsed laser is launched into the waveguide through a
beamsplitter by means of a lens. Backpropagated signal is collected with
the same lens, redirected through the beamsplitter, and focused with
another lens onto the entrance slit of a monochromator. Signal is
monitored with a photomultiplier tube. A small portion of the laser light
is directed to a fast photodiode by a mirror. The returned waveforms were
recorded with a digitizing oscilloscope; the oscilloscope is triggered by
the output from the fast photodiode. Each monitored waveform is averaged
over several laser pulses, transferred to a computer, and analyzed using
commercial software packages. Software packages for signal analysis are
LabVIEW from National Instruments (Austin, Tex.), Matlab (The Mathworks
Inc., Natick, Mass.), or others.
In addition to the cylindrical geometry for the embodiment shown in FIG. 3,
the waveguide may be of any cross-section or shape such that the coating
continuously covers the outer surface, except for at least one end, or
where non-coated surfaces are arranged on a non-permeable substrate.
Measurements of barrier properties are performable on different regions of
the waveguides using optical time-of-flight detection methods, for
example, as shown in FIG. 4, or using multiplexing techniques where each
coating is deposited on a different waveguide.
In addition to the application of indirect sensing methods that employ a
chemically sensitive reagent to flag the presence and concentration of an
optically inactive vapor, a variety of direct spectroscopic techniques are
capable of being utilized. These optionally include, for example,
ultraviolet (UV), near-infrared (near-IR), mid-IR methods, and
luminescence and Raman spectroscopies. For example, permeation of water
vapor through a barrier coating deposited onto a waveguide is measurable
in the near- and mid-IR spectral ranges. Also, pulsed excimer lasers
emitting in the vacuum UV range can be used to probe for absorption of
oxygen reaching the waveguide.
Thus, in summary, methods and devices have been disclosed for measuring
barrier properties of a barrier coating or coating arrays where each
barrier coating has a small cross section. To reduce the edge effects in
the measurements of barrier properties, measurements are made using a
waveguide structure coated with a chemically sensitive layer and an array
of barrier coatings. The coated waveguide is exposed to a material of
interest to produce an analyzable variation in the chemically sensitive
layer to detect an impact on the barrier coatings. In one variation, a
propagated wave, such as pulsed light, is propagated within the waveguide
structure, and the impact on the propagated wave are detected and
correlated to a value of a barrier property for each of the array of
barrier coatings.
Example embodiments of the present invention have now been described. It
will be appreciated that these examples are merely illustrative of the
invention. Many variations and modifications will be apparent to those
skilled in the art.
* * * * *
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