Introduction
This chapter will review aspects of soft random solids, including particulate gels, compressed emulsions, and other materials having similar basic features. Soft random solids are appealing for a number of reasons – and not just because of their taste (as in foods) or appearance (as in cosmetics). They offer the potential for insight into much broader and quite elegant problems in nonequilibrium thermodynamics such as the dynamics of phase transitions, the origin of the glass transition, and stresses and flows in granular media. They are also central players in a host of industries in the form of paint, ink, concrete, asphalt, dairy foods, and cosmetics. From the range of examples and the techniques involved, it should be apparent that investigation of these materials is a multi-disciplinary process, combining contributions from physicists, chemists, and engineers.
Since the 1980s, studies of soft random solids have benefited enormously from advances in microscopy, computer-aided image analysis, computer simulations, and new methods to synthesize colloidal particles with controlled shape, surface chemistry, and interactions. The chapter's purpose is to summarize areas of recent investigations and point out experimental breakthroughs, remaining questions, and relevant experimental methods. Despite the recent progress, a number of fundamentally interesting and practically relevant questions remain, and it is hoped that this chapter will stimulate further work in these areas.