Current Research

The dynamics of polymer nanofilms are different from those of the bulk polymer. Studies in the past three decades indicated that the differences are attributable to perturbations at the interfaces. According to the convention, the free surface (i.e., the air/vacuum interface) imparts enhanced mobility to the nearby polymer by virtue of the lower local density while a substrate surface may impart enhanced or reduced mobility if the polymer-substrate interaction energy, E_s, is positive (repulsive) or negative (attractive), respectively. Therefore, polymer films that display faster dynamics with decreasing film thickness, h, are attributed to the E_s being small or positive while those that display the opposite to having large, negative E_s. While this picture has been able to provide qualitative explanations to many experimental results, it is unable to address some experimental observations. Importantly, the fundamental question of how interfacial effects may persist over long distances from ~100 to ~1000 nm or ~10 to ~100 times the radius of gyration of the polymer (R_g) remains unanswered. Below are highlights of some of the past and ongoing works by us that address the issues (Click on the titles to access the details.)