SURFACE WRINKLES FOR WETTIBILITY AND THERMO-MECHANICAL MEASUREMENT
Jun Young Chung and Christopher M. Stafford
Surface wrinkling or buckling has recently become an attractive way for creating surface structures, characterizing material properties and even assisting in investigation of important physical phenomena. In this presentation, we examine two issues pertaining to surface wrinkles in bilayer systems consisting of thin films on elastic substrates.
The first issue concerns the wetting behavior on tunable anisotropic microstructures. Their wetting properties were examined by contact angle measurements perpendicular and parallel to the direction of the grooves. The results obtained show that the apparent contact angles in two orthogonal directions appear to be quite different; the one in the perpendicular view was larger than the other. Interestingly, although the surface is inherently hydrophilic the contact angle in the perpendicular view on the patterned surface increases with increasing surface roughness. We demonstrate that this phenomenon is attributable to both their surface morphology and the nature of the three-phase contact line structure.
The second issue investigates the wrinkling behavior under thermal loading. The wrinkling pattern forms spontaneously and self-assembles upon cooling of a pre-heated bilayer system. The thin film wrinkles since it experiences a different level of contraction due to thermal expansion mismatch. The critical temperature for wrinkling formation and the dominant wavelength of wrinkling are associated with both the thermal expansion coefficients and moduli of the film and substrate. An elegant, efficient methodology of measuring reliable thermal and mechanical properties of thin films emerges from well-established buckling mechanics. The feasibility of accurate critical temperature measurement is demonstrated by using an optical microscope, light scattering, and AFM. Furthermore, the thermal buckling and post-buckling behaviors are studied in detail both experimentally and theoretically.
Jun Young Chung
Postdoctoral Guest Researcher
Polymers Division, Materials Science and Engineering Laboratory
Polymer Bldg. (224), Rm. B216
Mail Stop: 8542
Telephone #: (301) 975-5732
Fax #: (301) 975-4924
Mentor: Christopher M. Stafford
Sigma Xi Member: No