Multi-lens Combinatorial Adhesion Test
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Introduction
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Motivation
We are developing a Combinatorial & High Throughput axisymmetric
adhesion test based on the Johnson, Kendall, and Roberts (JKR)
test geometry.
Objective
To create a measurement platform that allows a user to efficiently
conduct parallel adhesion tests across combinatorial libraries.
Traditional JKR tests utilize a single hemispherical lens to
measure the work of adhesion between the lens and a surface.
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 Figure
1: The axisymmetric adhesion test geometry. During testing the
contact radius (a), load (P), and displacement (d) are measured.
The work of adhesion is determined by fitting experimental load
and contact area data to the JKR model. |
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Experimental
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| The combinatorial approach utilizes an array of lenses to
conduct multiple parallel adhesion tests.
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| Figure 2: Profilometer images of the multi lens arrays. a)
image of a portion of the smaller lens array containing 1600
lenses over 1cm2. b) image of a portion of the larger lens array
containing 324 lenses over 3.25 cm2. Both images are 4 mm x
4 mm slices of their respective lens arrays. The inset drawing
shows the base PDMS film that supports the lenses.
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Benefits
each lens acts as a unique JKR test during one loading/unloading
cycle.
adaptable to investigation of gradient substrates.
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Challenges
size mismatch between lens and gradient.
informatics: image and data analysis for multiple JKR tests.
alignment of lens and substrate
load measurement
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Solutions
Design of experiment approach for sample
Informatics: utilizing automated image analysis and data maps.
Application of multi-axis tip/tilt control to bring lens arrays
and samples parallel.
Displacement based JKR modeling to quantify the work of adhesion.
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Results
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| Image Analysis |
 Figure
3: A Matlab based image analysis program was written to analyze
and record the contact areas of individual lenses throughout
the adhesion test. During analysis maps are created to show
the time each lens has been in contact with the substrate. These
are useful for qualitatively analyzing test results. |
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 Figure
4: Above is the contact radius as a function of displacement
for three different lenses during the loading and unloading
cycle. The displacement data has been shifted to account for
differences in the initial contact with the substrate. The solid
line is the fit of the data to the JKR model. What is important
is that all three lenses undergo the similar contact behavior.
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 Figure
5: We can also quantify the strain energy release rate, G, for
a series of lenses in contact with a substrate. G is the energy
required to remove the lens from the substrate. It is essential
for quantifying the velocity dependence of debonding processes.
The error represents one standard deviation in G. |
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Summary
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The multi-lens combinatorial adhesion test has
been shown to work for elastic materials on homogeneous substrates.
The displacement based measurement used for lens arrays works
well for these systems.
This technique can quantify adhesive bonding during both the
loading and unloading cycle of the adhesion test.
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Future Work
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Probing specific adhesive interactions by modifying lenses.
Extension into viscoelastic systems.
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NIST Contributors:
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| Aaron M. Forster, Wenhua Zhang, Arnaud Chiche, Seung-ho Moon,
Christopher M. Stafford
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