Mechanical properties and instabilities of PDMS surfaces

PMSE 149

M. D. Thouless, thouless@umich.edu1, K. L. Mills2, D. Lee2, S. Takayama3, J. R. Barber4, and N. Triantafyllidis5. (1) Departments of Mechanical Engineering and Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109, (2) Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109, (3) Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109, (4) Departments of Mechanical Engineering and Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI 48109, (5) Departments of Mechanical Engineering and Aerospace Engineering, University of Michigan, Ann Arbor, MI 48109
When the surface of the elastomer poly(dimethylsiloxane) (PDMS) is exposed to an oxygen plasma, a hard, relatively brittle surface layer is formed. Patterns, associated with either buckling or cracking can be created in this surface layer. These patterns can subsequently be used for a variety of nano- and bio-related applications. However, control of the patterns relies on understanding the mechanics of the pattern formation and being able to measure the properties and dimensions of the surface layers. This latter requirement is challenging owing to the very small thickness of the surface modified layer, and the uncertainty of how the material properties and stresses are distributed through the layer.

The application of a tensile strain induces periodic cracking instabilities within the brittle layer, and associated buckling in the transverse direction. Compressive loading induced buckling instabilities of the surface layer. Since it is anticipated that the method by which the surface-modified layer is formed in these materials results in a graded distribution of properties, analyses of buckling on elastic foundations were extended to incorporate the effects of grading. The properties of the surface-modified layer were deduced using AFM techniques, so as to provide a comparison with the predictions of analyses of the buckling and cracking instabilities.