报告题目: Particle dynamics in dense short-ranged attractive colloidal glasses
报 告 人: Piotr Habdas教授， 美国Saint Joseph's University
报告时间: 2012年09月24日 上午9:30
报告摘要：Colloidal suspensions are very important for applications ranging from cosmetic to food products. Moreover, liquid suspensions of colloidal particles can behave in the same way as much smaller counterparts in molecular glasses. The use of colloidal particles as 'big' atoms allows for a better understanding of the nature of the glass transition and nature of various glassy states. The nature of the glass transition is considered as the holy grail of the soft condensed matter.
Also, there may be a universal jamming transition that describes how materials change from unjammed to jammed state. Currently, jamming is an idea and there may be several jamming transitions with significant differences between them. I will discuss how colloidal suspensions fit within this theory.
Specifically, we study colloidal particle dynamics using confocal and fluorescence microscopy as the sample evolves from a repulsive glass towards an attractive glass. Short-range depletion forces induce this transition. We identify particles that exhibit substantial motional events and characterize the transition using the properties of these motional events. It appears that number of particles that exhibit motional events doesn't change as the system is brought from a repulsive glass towards the attractive glass.
Moreover, we investigate vibrational properties of these dense colloidal suspensions by focusing on the colloidal particles that do not exhibit substantial motion. Our preliminary results show that the boson peak for an attractive glass is lower than that for a repulsive system and it is shifted towards higher frequencies. To our knowledge, this is one of the first experimental investigation of the evolution of vibrational modes in hard-sphere like colloidal glasses when particle interaction potential changes from repulsive to attractive.
报告人介绍： Piotr Habdas received his Master and PhD degree from University of Silesia, Poland. Next he was a postdoctoral fellow at Memorial University of Newfoundland，Canada and at Emory University, USA. He joined Saint Joseph's University as an assistant professor in 2004. Currently he is an associate professor at Saint Joseph's University in Philadelphia, PA. His research interests include colloidal glass transition, non-Newtonian liquids, and use of novel porphyrins in photodynamic therapy.