Understand the Complex Structural Organization of Soft Materials in Confinement
Yu-qiang Ma
National Laboratory of Solid State Microstructures, Nanjing University

In this talk, I first present a simple review of self-organizing behaviors in soft materials, and then examine in detail the physical mechanism of self assembly / self organization in confined soft materials on the basis of some examples of our recent works on colloidal assembly in polymer templates and lateral organization in inclusion-membrane complexes. I try to discuss how to design and control the ordering of these systems in confinement (e.g., via using polymer and/or biomembrane as templates), and how to understand the influence of the competition between the excluded volume effect of colloidal particles and the conformational entropic effect of (polymer or lipid) chains on complex structural organization.

Bio:
Professor Yu-qiang Ma received his Ph.D. in Physics from Nanjing University in 1993. Currently, he is a professor at Department of Physics of Nanjing University, and is also a Principal Investigator of National Laboratory of Solid State Microstructures. In 1999, Prof Ma received the National Science Fund for Distinguished Young Scholars in China, and in 2001, he was appointed as a Chang-Jiang Professor by the Ministry of Education in China. Prof Ma's current research interests are in area of physical understanding of self assembly/self organization in soft matter. His recent projects include phase transitions and dynamics in complex fluids such as colloid and polymers, lateral organization in protein-membrane complexes, and nonequilibrium self-organization in living soft matter such as cellular cytoskeleton and self-propelled particles.

The Role of Hydrogen Bonding in Polymeric Systems
Chun-lai Ren
National Laboratory of Solid State Microstructures, Nanjing University

A molecular theory is used to study the hydrogen bonding in polymer solutions. For a tethered poly(ethylene oxide) (PEO) layer in water, including polymer-water and water-water hydrogen bonds, the solubility of PEO decreases with the increasing temperature and results in a collapse of the layer at high enough temperatures. This should be contributed to the broken of hydrogen bonds at high temperatures. Furthermore, we study the aggregating behavior of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO). Due to the hydrophobic nature of PPO, micelles appear above the critical micellization concentration (CMC). Our theoretical prediction shows that CMC decreases with the increasing of temperature.

An AFM-based Hanging Fiber Rheometer for Interfacial Microrheology
Shuo Guo
Department of Physics, The Hong Kong University of Science & Technology

Compared to a large number of theoretical investigations and numerical simulations, experimental studies of micro-scale hydrodynamics near the contact line between the solid-liquid interfaces are rather limited. This is partially due to the fact that direct measurements of the fluid motion and viscous drag in the immediate vicinity of the contact line are not accessible by conventional optical techniques. In this talk, I will describe a new microrheology technique using atomic force microscope (AFM) as a force sensor. The probe contains a long vertical glass fiber with one end glued onto an AFM cantilever and the other end immersed through a water-air interface. The motion of the modified cantilever can be accurately described by the Langevin equation, from which we obtain the friction coefficient of the glass fiber in contact with the water. The experiment demonstrates that the hanging fiber rheometer is a very sensitive devise to measure minute drag forces produced by the contact line between the water-air interface and the glass fiber. This technique opens a door to a wide variety of important experiments for the studies of interfacial microrheology and contact line dynamics.