Molecular and Phase Chirality in Polymer Networks – Eugene Terentjev

Date: Thu. April 7th, 2005, 4:15 pm-5:15 pm
Location: Rockefeller 301

Nature appears to be inherently chiral. From the atomic scale with asymmetric carbon bonds, to much larger length scales like our hands or even spiral galaxies, all have the same common feature of lacking inversion symmetry, while not characterized by any vector (dipolar) property. In other words, many natural objects “know” the difference between right and left. This is the notion of chirality; since Pasteur and Kelvin in the mid-19 century it has always been a source of interest in various fields, from mathematics to medicine. Although stereo-specific intermolecular interactions are always very weak, there are many examples of macroscopic “phase chirality” emerging, as a coherent arrangement of molecules or groups over large distances. Cholesteric liquid crystal is one, and the helical secondary structure of biopolymers is another. In this colloquium we shall examine physical effects arising specifically from such phase chirality in polymer networks. First, we consider an imprinted cholesteric state and its property of stereo-selective swelling in solvents of different chirality. The second example demonstrates the non-monotonic changes in the degree of helicity of protein chains by mechanical stretching.