Capillary Diodes with Selective Oil-Water Wetting Dynamics

1605809 Colosqui, Carlos This project will examine an innovative approach for separation of water and oils, generally defined as organic compounds insoluble in water, by tuning the in wetting/de-wetting dynamics of drainage and absorption dynamics in engineered porous media. This project will advance the fundamental knowledge of (dynamic) wetting and liquid adhesion on "real" surfaces having complex nano- and microscale structure. The new knowledge will advance technologies for anti-fouling, drag reduction, and micro/nano-fluidic handling, having large impacts on the U.S. economy, infrastructure, and the environment. Recent theoretical developments by the PI indicate that the dynamics of the wetting process, present nontrivial regimes not described by conventional continuum-based and deterministic predictions. These theoretical predictions have been confirmed by molecular dynamics simulations and, more recently, through experimental work by the PI's group and other groups. Building upon these developments this project will examine the feasibility of exploiting novel phenomena such as the crossover from capillary-driven to thermally-activated wetting for innovative technical applications. The accomplishment of specific research objectives will be enabled by interdisciplinary and complementary skills of the PI and Co-PIs. To understand this will require incorporating the effects of thermal motion of the contact line which dominate the dynamics as mechanical equilibrium is approached. This project aims to generate fundamental knowledge required to understand and control the dynamics of spontaneous and forced imbibition or drainage in nano/microstructured media such as synthetic filters, sponges, and fabrics, or soil, sandstone, and biological membranes. The research hypothesis this project will examine is that significant asymmetries in wetting/de-wetting dynamics (wetting hysteresis) of different liquid pairs on micro/nanostructured surfaces can be designed and controlled to engineered capillary "diodes" for efficient separation of immiscible liquids. The PIs approach to test this hypothesis is to use the surface nano/microstructure to control dynamic hysteresis effects that will lead to fast or slow (arrested) wetting depending on the direction of motion of the wetting line and physicochemical properties of the liquids (e.g., viscosity, density, interfacial tensions). The central objective of this project is to generate fundamental knowledge required to understand and control the dynamics of spontaneous and forced imbibition/drainage by different liquid pairs on nano/micro-structured media such as synthetic filters, sponges, and fabrics, or soil, sandstone, and biological membranes. Building upon theoretical developments and preliminary experimental results the project has two specific objectives: (1) Tuning the crossover points between fast and slow wetting regimes; (2) Controlling the relaxation rate in the slow (kinetic) regime. Theoretical predictions will guide the selection of experimental parameters and physical conditions to accomplish two specific objectives: (1) Tuning the crossover point between fast and slow wetting regimes; and, (2) Controlling the relaxation rate in the slow (kinetic) regime. The proposed research has the potential to be highly transformative to environmental remediation and water treatment. The engagement of students and underrepresented minorities is extensive from graduate education to K-12.