Tuning the Relaxation of Nano-Patterned Polymer Films with Polymer-Grafted Nanoparticles: Observation of Entropy-Enthalpy Compensation
Sonal Bhadauriya, Xiaoteng Wang, Jack F. Douglas, Praveen Pitliya, Jianan Zhang, Dharmaraj Raghavan, Michael R. Bockstaller, Christopher M. Stafford, Alamgir Karim
Polymer films provide a versatile plastic material in which complex functional relief patterns can be imprinted with a resolution down to tens of nanometers. However, the utility of such patterned materials is limited by the tendency of imprinted patterns to relax back to their original flat film state. We show that we can greatly improve the thermal stability of these nano-patterned features in poly(methyl methacrylate) (PMMA) films by incorporating PMMA- grafted titanium dioxide nanoparticles (NPs) into the polymer matrix. The observed stabilization of the nanoimprinted patterns with increased grafted NP concentration is found to be associated with the slowing down of film relaxation dynamics upon adding NPs. Specifically, the activation energy and entropy of the slumping relaxation time is found to obey an entropy- enthalpy compensation (EEC) relationship with varying nanoparticles concentration, as found recently in the relaxation of strain-induced wrinkles in polymer films as the film thickness is varied.