Dr. Taiki Hoshino, RIKEN, SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan; JST-PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan

Biography: Taiki Hoshino received his PhD from Kyoto University in 2009. From 2009 to 2014, he worked as a researcher in ERATO Takahara Soft Interfaces Project, Japan Science and Technology Agency. He has been working at RIKEN, SPring-8 Center as a research scientist, and JST-PRESTO researcher (2014-present). His research activities mainly focus on dynamical behavior of soft materials using coherent X-ray scattering techniques.

Speech Title: Dynamics of Polymer Interfaces studied by X-ray Photon Correlation Spectroscopy
Abstract: Dynamical fluctuations of polymer interfaces play crucial roles for their functionality such as adhesion and wettability. X-ray photon correlation spectroscopy (XPCS) is a powerful technique, using partially coherent X-rays, for understanding a variety of microscopic dynamic phenomena. Using XPCS techniques, we have studied some of dynamical behavior of polymer interfaces. The stability of polymer thin films is important in applications such as coatings and dielectric layers. Adding polyhedral oligomeric silsesquioxanes (POSS) to thin films is an efficient way to prevent them from dewetting. The surface dynamics of POSS-functionalized polystyrene (PS-POSS) thin films above the glass transition temperature were studied by XPCS. Much slower fluctuations were observed in the surface of PS-POSS thin films than in the polystyrene thin films, despite the negligible difference in their bulk viscosity. Quantitative analysis based on fluctuation-dissipation theorem indicated that there is a high-viscosity layer at the surface of the PS-POSS films, and that the substrate interface originated from POSS segregation. We also studied the dynamical behavior of PS grafted silica nanoparticles dispersed in a PS matrix. The nanoparticles exhibited non-Brownian behavior, and as the temperature increased, the crossover from hyperdiffusion to subdiffusion occurred. The detail of results and discussion will be presented.
Keywords: Surface dynamics, Polymer thin film, X-ray photon correlation spectroscopy, silsesquioxane, Nanoparticle