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Design of Experiments for High-Throughput Adhesion Mapping

 
Aaron M. Forster, Christopher M. Stafford, Eric J. Amis, Alamgir Karim
 

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.