Influence of Solvent Quality on the Relaxation Time of Polymer Films Ophelia K. C. Tsui, Boston University, DMR Spin-coating is a commonly used method for making polymer films. It has long been suggested that polymers in the films produced by this method are highly non- equilibrated because there is little time for the polymer chains to equilibrate as the solvent in the film evaporates rapidly in the spin-coating process. We measure the relaxation time of polymer films spin-coated at different temperatures across the  -temperature, T . The purpose of changing the coating temperature across T  is to adjust the degree of extension of the polymer chains as demonstrated by the curved line in the plot at right, and hence the overlap between neighboring chains. The data clearly shows a strong, positive correlation between the relaxation time and the degree of chain overlap. This result shows that adjusting the chain conformation in a solution may provide an effective route of adjusting the properties of a spin-coated film. Relaxation time as a function of the temperature at which the polymer films were cast (red squares). The  -temperature of the polymer/solvent system is marked by the vertical line. The curved solid line denotes the diameter of the polymer normalized to that at the  -temperature.

 Co-organized, with Prof. J. A. Forrest of the University of Waterloo, the invited symposium, Dynamics of Nano-Confined Polymer Films in the 2010 APS March Meeting.  Co-organizing the symposium, Surface and Interfacial Rheology with Prof. L. Dai of Arizona State University for the Society of Rheology 2010 Meeting, Santa Fe, NM.  2 refereed journal articles 1,2 were published and one was submitted 3.  8 presentations were given in professional conferences or academic institutions. 1 Y. Fujii, Z. Yang, J. Leach, H. Atarashi, K. Tanaka and O. K. C. Tsui, “Affinity of Polystyrene Films to Hydrogen-Passivated Silicon and Its Relevance to the Tg of the Films”, Macromolecules, 42, 7418 (2009). 2 Y. Fujii, Z. Yang and O. K. C. Tsui, “Shear Modulus of a Polymer Brush”, Macromolecules, 43, 4310 (2010). 3 Z. Yang, D. Peng, A. Clough, C. -H. Lam and O. K. C. Tsui, “Is the Dynamics of Polymer Films Consistent with Their Tg?", Eur. Phys. J. Special Topics (submitted). Education: Ophelia K. C. Tsui, Boston University, DMR Training of 4 graduate students and 1 undergraduate student. Below are some highlights.  Graduate student, Andrew Clough of Boston University (USA) gave an oral presentation at the 2010 APS March Meeting, Portland, OR. There, he also met Prof. Günter Reiter, the German partner of this MWN and Prof. Jörg Baschnagel of Université de Strasbourg, and gave them a powerpoint presentation summarizing the works and results he had achieved.  Graduate students, Dongdong Peng and Andrew Clough of Boston University first co-authored a paper.  Graduate student, Adam Raegan of Universität Freiburg (Germany) gave two oral presentations, one at the Makromolekulares Kolloquium, Freiburg and one at the 2010 APS March Meeting.  Undergraduate student, Jessica Leach of Boston University co- authored a paper with the PI. She graduated in May this year and will start a Master program in education at the School of Education in Boston University this fall. Outreach: Graduate student, Andrew Clough of Boston University preparing samples in Tsui’s laboratory.