The mixing of polymers and nanoparticles is opening pathways for engineering flexible composites that exhibit advantageous electrical, optical, or mechanical properties. Recent advances reveal routes to exploit both enthalpic and entropic interactions so as to direct the spatial distribution of nanoparticles and thereby control the macroscopic performance of the material. For example, by tailoring the particle coating and size, researchers have created self-healing materials for improved sustainability and self-corralling rods for photovoltaic applications. A challenge for future studies is to create hierarchically structured composites in which each sublayer contributes a distinct function to yield a mechanically integrated, multifunctional material.

Dynamic Surfactants: Surfactants are used to form a stable interface between two nonmiscible liquids, like oil and water, so that droplets of one fluid can be entrained in the other. Cui et al. (p. 460 ) designed a surfactant based on the association of a hydrophilic nanoparticle with a functionalized oleophilic molecule that self-assembles at a water-oil interface to produce a composite surfactant. Once adsorbed, the nanoparticles tend to remain in place causing them to accumulate and “jam” at the interface. When a drop was deformed, more surfactant could assemble at the surface, allowing droplets of various shapes to be produced.