The “New” Science of “Complex Fluids”

We present an overview of the modern study of complex fluids which, because of the overwhelming breadth and richness of this field, unavoidably neglects many interesting systems and research developments. In proposing a definition of the field, we discuss first the special role played by phenomenological theory and the limitations of molecular-level description. The remainder of the article is organized into sections which treat model colloids, micellized surfactant solutions, interfacial films and microemulsions, bilayers and membranes, and new materials. In each instance we try to provide a physical basis for the special nature of interactions and long-range ordering transitions in these novel colloidal and thin layer systems. At the heart of understanding these highly varied phenomena lie the curvature dependence of surface energies and the coupling between self-assembly on small length scales and phase changes at large ones.