Equilibrium Pathway of Polymer Nanometer Films Equilibrium Pathway of Polymer Nanometer Films Ophelia K. C. Tsui, Trustees of Boston University, DMR Viscosity vs. Temperature of 80 nm thick, M w = 2.4 kDa monodispersed PS films spin-coated on silicon. The viscosities were obtained by analyzing the surface evolution of the films during annealing at the experimental temperatures. The solid line represent published data of bulk PS with the same molecular weight. When polymers are adapted for an application, they generally end in a non-equilibrated state. This is because most polymers are glassy at the room temperature, when they are brought back to ambience upon processing, they often suffer kinetic arrest at the glass transition, which prevents them from reaching equilibrium. In this work, we focus on polymer nanometer films prepared by spin-coating, which is a broadly used methods of making them. Numerous experiments showed that these films are highly non-equilibrated, which raises concerns about their stability and therefore usage in nanoscale applications. By monitoring the temporal evolution of the surface structure of freshly spin-cast polystyrene (PS) films on Si with molecular weights, 2.3 ≤ M w ≤ 393 kg/mol, we find that the measured dynamics are consistent with thermalization of surface capillary waves on the films. Modeling of the data based on this equilibration scheme produces excellent agreement between the viscosity of the studied films and the bulk (figure at right). This result provides compelling evidence that the metastability of as-prepared polymer films primarily arises from the discrepancy between its surface structure and the equilibrium.

Education: Training of 2 post-doctoral fellows, 1 graduate student, 5 undergraduate students and 1 high-school senior. Highlights:  Graduate student Tzong-Ru Han gave his first conference presentation at the 9th Annual Greater Boston Area Statistical Mechanics Meeting.  Physics major Lela Todorova (class of ’08) wrote two proposals applying for funding from BU’s Undergraduate Research Opportunity Program to work in the PI’s lab. and both were funded. In Jan., 2008, she attended the Conference for Undergraduate Women in Physics at Yale and presented her results.  High-school intern Elliot Greco gave a poster presentation in the Workshop for the Boston University High School Honors Research Internship Program in Outreach:  Academic advisor to BU’s Women in Physics, a university student organization aimed at fostering an environment that promotes female physicists.  The PI showcased her research lab. to some 50 visitors during BU’s Physics Open House.  2 refereed journal articles and 1 book chapter were published 1 or submitted 2-3.  6 presentations were given in professional conferences and/or academic institutions. BU Physics senior Lela Todorova (class of ’08) and postdoctoral fellow Zhaohui Yang are loading a sample to the group’s atomic force microscope. Elliot Greco of Marine Academy of Science & Technology, NJ is giving a talk to the PI’s group summarizing his work during Jul-Aug 2007 when he took a summer research internship with the PI. Ophelia K. C. Tsui (Boston University) DMR O. K. C.Tsui, Y. J. Wang, F. K. Lee, C. -H. Lam, Z. H. Yang, Macromolecules 41, (2008), 2 O. K. C.Tsui, Chapter 11 in Polymer Thin Films, eds. O. K. C. Tsui, T. P. Russell, World Scientific (to appear) 3 Z. H. Zhang, Y. J. Wang, L. Todorova and O. K. C. Tsui (submitted).