The freedom of confinement in complex fluids

Although easily overlooked, complex fluids - non-Newtonian, typically multiphase fluids - are ubiquitous and play an integral role in our daily lives. In nature, examples run the gamut from particle dispersions (such as saps, mud, blood, and lava) to high-molecular-weight polymers (like DNA and proteins), to aggregates of low-molecular-weight surfactants (such as lipids). Complex fluids include such familiar products as shampoo, detergents, shaving cream, chocolate mousse, paint, glue, and liquid-crystal-based displays. Their multiple, coexisting phases give rise to a hierarchy of length and time scales not seen in conventional fluids; the interactions between those phases can yield fascinating properties and behavior. See, for example, reference 1 and previous PHYSICS TODAY articles by Thomas Witten (July 1990, page 21), Alice Gast and William Russel (December 1998, page 24), and Pierre-Gilles de Gennes (June 1983, page 33).