Dynamics and Surface Layer Mobility of Polymer Dynamics and Surface Layer Mobility of Polymer FilmsFilms

Ophelia K. C. Tsui, Boston University, DMR 0706096

Most polymers solidify into a glassy amorphous state, accompanied by a rapid increase in the viscosity when cooled below the glass transition temperature (Tg). There has been an on-going debate on whether the Tg ganges with decreasing polymer film thickness, and the origin of the changes.

We measure the viscosity, n, of unentangeld, short-chain polystyrene films on silicon at different temperatures. As the data at right shows, the transition temperature for going from a low-n to a high-n state decreases with decreasing film thickness, h (where 2.3≤h≤79 nm), consistent with the changes in the Tg of the films observed before.

By apploying the hydrodynamic equations to the films and assuming the films to possess a highly mobile liquid layer following Arrhenius dynamics at the free surface (as shown in the schematic at right), we are able to explain the data fully (solid lines in the plot at right).

This work is published in Science, 328, 1676 (2010).

Dynamics and Surface Layer Mobility of Polymer Dynamics and Surface Layer Mobility of Polymer FilmsFilms

Ophelia K. C. Tsui, Boston University, DMR 0706096Education:Training of 2 post-doctoral fellows, 2 graduate students, 1 under-graduate student and 1 high-school senior. Below are some highlights.

• Postdoctoral fellow, Dr. Yoshihisa Fujii gave an oral presentation at the 11th Annual Greater Boston Area Statistical Mechanics Meeting. This January, he was offered an assistant professorship in Kyushu University, Japan.•Postdoctoral fellow, Dr Zhaohui Yang gave a poster presentation at the Nanomedicine Symposium in Boston University.•Physics graduate student, Andrew Clough gave his first oral presentation at the 11th Annual Greater Boston Area Statistical Mechanics Meeting.•High-school intern Jacob Rubash gave an oral presentation to the group towards the end of his summer internship and a poster presentation in a local workshop organized by Boston University.

Outreach:•Academic Advisor to the Boston University Women in Physics, a student organization aimed at fostering an environment that promotes female physicists.•Co-editing the 2010 special edition of The Journal of Polymer Science, Part B: Polymer Physics with Prof. Thomas H. Epps, III of University of Deleware for the Division of Polymer, American Physical Society.•As the Global Centers of Excellence Lecturer of Kyushu University, Fukuoka, Japan, the PI delivered four 1.5-hour lectures on “Interfacial Properties of Polymer Films” to Kyushu University’s graduate students in the Faculty of Engineering.•2 refereed journal articles1-2 including one in Science.•4 Presentations were given in professional conferences or academic institutions.

•1. Z Yang, CH Lam, E DiMasi, N Bouet, J Jordan-Sweet, and OKC Tsui. “Method to measure the viscosity of nanometer liquid films from the surface flucturations,” Appl. Phys. Lett, 94. 251906 (2009).•2. Z Yang, Y Fujii, FK Lee, CH Lam, and OKC Tsui, “Glass Transition Dynamics and Surface Layer Mobility in Unentangled Polystrene Films,” Science, 328, 1676 (2010).