Network formation in suspensions of colloids and liquid crystal: reversibility – memory effects

Abstract

Suspensions of colloids, thermotropic low molecular weight liquid crystal, and small amounts of alkane are investigated by laser scanning confocal microscopy and calorimetry. While cooling the suspension through the isotropic-nematic phase transition the colloidal particles are expelled by the liquid crystal, causing the formation of a three-dimensional particle network. Upon reheating back into the isotropic phase the network may break up. However, taking the sample a number of times through the cooling/heating cycle leads to annealing of the network, accompanied by an increase of the loss modulus of the system by several orders of magnitude. Eventually it hardly breaks up, even after resting in the isotropic phase for several hours. Calorimetric studies reveal that in this case, the temperature dependent heat capacity of the system contains two peaks.

Acknowledgements: The authors thank Wilson Poon for bringing the topic to their attention. We have benefited form discussions with Günter Auernhammer, Mike Cates, Julie Cleaver, Harald Pleiner, Sara Romer and Jürgen Vollmer. The authors are grateful to Beate Ullrich for detailed comments on the manuscript. D. V. acknowledges funding by the European Commission under the Marie Curie program. A.B.S. is supported by the NASA Microgravity Sciences Program.