The work is a fundamental investigation of the viscoelastic response of ultrathin polymer films in two different conditions. The work will compare, contrast, and seek origins of differences between the nanobubble inflation method developed by the PI at Texas Tech University and the liquid dewetting method developed by Bodiguel and Fretigny in Paris (which are the only methods currently available to measure the viscoelastic response of unsupported films). The two techniques had shown substantial differences in glass transition temperatures as functions of film thickness. The two methods differ in that one measures films with free surfaces and the other measures films floating on a mobile substrate. The planned research will examine the effects of changing substrate, molecular weight, and molecular architecture on the viscoelastic properties of ultrathin polymer films. It will explore the hypothesis that the relevant differences in confinement behavior are related to very subtle differences in surface energy/surface interactions and will provide new data focused on the understanding of how surfaces and interfaces impact the dynamics of polymers confined to the nanometer size scale.
NON-TECHNICAL SUMMARY:
The dramatic influence of nanoscale confinement on material behavior is exemplified by the response of ultrathin polymer films that show tremendous property changes, for example, in freely suspended films having nanometer thicknesses. Yet the origins of these changes are not yet elucidated. The present work probes these changes using two novel nanomechanical test methods. The work compares and contrasts mechanical properties of a series of polymers having different molecular characteristics. In addition, because there is such a strong apparent effect of the environment seen by the film surface, the work probes the behavior of the ultrathin polymer films exposed to liquids having different properties. The research provides new data in the understanding of how surfaces and interfaces impact the mechanics of polymers confined to the nanometer size scale. The project also has an important component that trains graduate students and, in addition to their scientific training, involves them in a STEM outreach program to young girls through the "Science: It's a Girl Thing" Program at Texas Tech University.
