Mechanical Stability of Polystyrene and Janus Particle Monolayers at the Air/Water Interface.

The compressional instability of particle-laden air/water interfaces is investigated with plain and surface-anisotropic (Janus) particles. We hypothesize that the amphiphilic nature of Janus particles leads to both anisotropic particle-particle and particle-interface interactions that can yield particle films with unique collapse mechanisms. Analysis of Langmuir isotherms and microstructural characterization of the homogeneous polystyrene particle films during compression reveal an interfacial buckling instability followed by folding, which is in good agreement with predictions from classical elasticity theory.

Temperature-Induced Collapse, and Arrested Collapse, of Anisotropic Endoskeleton Droplets.

Micron-scale rod-shaped droplets with a range of aspect ratios are produced using extrusion of oil containing a soft wax crystal network to permit shape customization. A physical model of the droplet shape stability is developed based on balancing interfacial stresses with the internal crystal network yield stress. The model predicts the mechanical properties required for particular droplet size stability, in a given physicochemical environment, and is tested by microscopic observations of droplets over a range of relevant applied temperatures.

Interfacial stability and shape change of anisotropic endoskeleton droplets.

The delivery of suspended active ingredients to a surface is a central function of numerous commercial cosmetic, drug, and agricultural formulations. Many products use liquid droplets as a delivery vehicle but, because interfacial tension keeps droplets spherical, these materials cannot exploit the benefits of anisotropic shape and shape change offered by solid colloids. In this work, individual droplet manipulation is used to produce viscoelastic droplets that can stably retain non-spherical shapes by balancing the Laplace pressure of the liquid-liquid interface with the elasticity of an internal crystalline network.