Adhesion Behaviour between a Nanostructured Bijel Film and Support Substrate

Abstract

With increasing world population and water demand, water scarcity is a global issue that is stressed every year by the United Nations. To address this issue, reverse osmosis (RO) membranes play a central role in converting saline water into freshwater. Thin films nanocomposite (TFN) can potentially be used in RO membranes to enhance freshwater quality and increase freshwater production. Bicontinuous interfacially jammed emulsion gels (Bijels) films are potential candidates for the fabrication of TFN. A bijel consists of two intertwined immiscible channels kinetically stabilized with functionalised-silica NPs, resulting in a bicontinuous structure. A bijel film is fragile and requires a porous polymer support to enhance its mechanical stability. The wetting behaviour of a bijel film onto a polymer substrate is investigated in this thesis. A hydrophilic bijel precursor mixture is extruded onto a polymer film using a roll-to-roll device. We hypothesized that the wetting of a bijel precursor onto a hydrophilic substrate leads to high wetting and, thus, high adhesion. We demonstrated that a printed bijel film adheres poorly onto a hydrophobic support. The hydrophilicity of polyvinylidene difluoride (PVDF) membranes was improved via a two-step coating method using poly(vinylpyrrolidone) (PVP, 1, 2, 5, and 10 wt%) and tannic acid (TA, 10 mg/mL). Characterising the wetting properties of functionalised membranes was performed via dynamic contact angle measurements and UV-Vis. UV-Vis allowed us to estimate the concentration of TA adsorbed onto the surface of a PVDF film. We hypothesized that increasing PVP's concentration would result in increasing hydrophilicity of a surface. Instead, a maximum in hydrophilicity was observed at a 2 wt% PVP concentration. Still, the membranes remained too hydrophobic in toluene. In a second part, a bijel film was fabricated via dip coating and the bijel-substrate interface could be observed using confocal laser scanning microscopy. Observing the wetting of a bijel film onto a hydrophilic substrate in toluene was not achieved in this thesis. Further research into the surface modification method is required to obtain support substrates with higher hydrophilicity. This would allow us to draw better conclusions regarding the adhesion behaviour of a bijel precursor onto a hydrophilic polymer substrate to obtain a bijel film.