Design of Experiments
for High-Throughput Adhesion Mapping
Polymers Division, Materials Science and Engineering Laboratory (MSEL),
National Institute of Standards and Technology,
Gaithersburg, MD 20899
Abstract
The multi-lens combinatorial adhesion test is a high-throughput
adhesion test method based on the Johnson, Kendall, Roberts (JKR) theory.
In a typical JKR test, the work of adhesion is measured quantitatively
using a single spherical indenter brought into contact with an opposing
flat substrate through a loading and unloading cycle. The multi-lens
technique employs an array of miniaturized spherical lenses to conduct
a large number of adhesion tests during oneloading/unloading cycle.
The size of a lens array may range from several hundred to more than one
thousand lenses. Given this large number of lenses, this test is
uniquely suited for investigation of combinatorial libraries that contain
orthogonal gradients in experimental parameters such as temperature, surface
energy, or roughness. One drawback to conducting such a large number of
adhesion tests lies in data analysis. A typical continuous gradient
library spans an area of 20 cm2 and several loading/unloading
experiments, each representing hundreds of JKR experiments, are required
to create an adhesion map of the surface. The potential for data
overload is great, given the large number of images collected throughout
the loading and unloading cycle.
Design of experiments (DOE) is a statistical approach to analysis of
the gradient library and a potential solution to this problem. The
gradient library is first tested in a few areas distributed throughout
the sample, e.g., a rational starting point may be to measure adhesion
at the sample corners and sample center. From these simple initial
tests, the gradient most relevant to adhesion is modeled. Subsequent
analysis of the sample is focused along this gradient to create a representative
surface map rather than a complete mapping of adhesion across the entire
substrate. We will discuss the application of this technique to measure
the adhesion across a polydimethylsiloxane substrate containing a gradient
in crosslink density.