Jurg Hulliger
University of Berne, Switzerland
Title: Orientational Disorder of Dipolar Molecules: a Key to understand Polarity Formation in Materials
Biography
Biography: Jurg Hulliger
Abstract
Dipolar molecules (low molecular weight up to macromolecular) entering solid matter by a mechanism of growth can produce macroscopic effects of polarity. Here, we will review theoretical and experimental results on a stochastic mechanism leading to polarity in molecular crystals, inorganic-organic biomimetic materials and natural tissues. Monte Carlo model and molecular dynamics simulations support a so called bi-polar state in all these cases. The bi-polar state is characterized by two adjacent polar domains of opposite orientation of the polarization.rnExperimentally, the spatial distribution of polarity in materials was investigated by scanning pyroelectric (SPEM) and phase sensitive second harmonic generation microscopy (PS-SHG). These two advanced techniques allowed us for the first time to demonstrate the theoretically predicted reversal transition in molecular crystals nucleating into a polar structure, developing then two adjacent domains of opposite polarization. Similarly, PS-SHGM was applied to a first determination of the absolute polarity distribution in teeth cementum.rnTheoretical and experimental work on various materials allow us to conclude, that in general a bi-polar state represents the statistical ground state of materials made of dipolar constituents. For further introduction, see review by J. Hulliger et al., New J. Chem., 37, 2229-2235, 2013. Theoretical issues may be recovered from J. Hulliger et al., Cryst. Growth Des., 12, 5211-5218, 2012.rn