Colloid Science Collides with Liquid Crystals

摘要

Brownian motion-the chaotic movement of colloidal particles that results from their collisions with solvent molecules-controls transport processes in systems as complex as the interior of living cells and as mundane as a film of drying paint. In a simple solvent, if you measure the distance the colloid travels (its displacement) for a sufficiently long time, the disorderly motion obeys a simple relation: The mean squared displacement (MSD) scales linearly with time. However, more recent studies of complex systems (e.g., concentrated solutions of proteins, polymers, or surfactants) revealed deviations from this classical behavior caused by local fluctuations in the composition and structure of the medium around the colloid (1-3). Now, in a strikingly elegant study described on page 1351 of this issue, Turiv et al. (4) unmask a new example of "anomalous diffusion" of colloids that involves a liquid crystal (LC), a liquid-like phase that has long-range orienta-tional ordering. Fluctuations in the solvent-molecule orientations cause MSDs of colloids to grow nonlinearly with time.