Tuning thin-film bijels with applied external electric fields.

The tunability of thin-film bijels using applied external electric fields is explored using a Cahn-Hilliard Langevin dynamics computational model. Dielectric contrast between liquid domains governs liquid domain alignment and was varied in the simulations. Dielectric contrast between colloidal particles and liquid matrix induces dipolar particle interactions and was also varied in the simulations. The study reveals unique internal morphologies including those with through-thickness liquid domains. Significant results include identification of electric field effects on phase evolution and final morphology as well as relevant mechanisms. It was also found that particle chains act as nucleation sites for phase separation. The resultant morphologies were analyzed in terms of particle attachment to phase interface regions as well as the average channel diameter. Electric field effects and mechanisms on morphology are identified and compared with other morphology-tuning parameters such as particle loading and liquid-liquid composition.

Diverse morphologies in thin-film bijels by varying film thickness and composition.

Thin-film bijels have many potential energy and environmental applications. In this work, the metastable bijel morphology space in thin-film confinement is explored with a Cahn-Hilliard/Brownian-Dynamics computational model. The key parameters varied are the bijel liquid phase blend ratio and the bijel film thickness. Simulations reveal a broad spectrum of structurally unique morphologies that have yet to be observed in experiments and which could have interesting applications in membrane science and other domains. Extensive analyses of surface-to-volume ratios, interfacial particle attachment statistics, and topological interfacial curvatures within the bijels are presented for a complete characterization of the morphological structure.

Numerical simulations of bijel morphology in thin films with complete surface wetting.

Bijels are a relatively new class of soft materials that have many potential energy and environmental applications. In this work, simulation results of bijel evolution confined within thin films with preferential surface wetting are presented. The computational approach used is a hybrid Cahn-Hilliard/Brownian dynamics method. In the absence of suspended particles, we demonstrate that the model accurately captures the rich kinetics associated with diffusion-based surface-directed spinodal decomposition, as evidenced by comparison with previous theoretical and simulation-based studies. When chemically neutral particles are included in the films, the simulations capture surface-modified bijel formation, with stabilized domain structures comparable with the experimental observations of Composto and coworkers. Namely, two basic morphologies - bicontinuous or discrete - are seen to emerge, with direct dependence on the film thickness, particle volume fraction, and particle radius.