No abstract

Hydrophobization of metal surfaces is reported based on silanization reactions. The aim was its application to metal porous membranes for the production of water in oil emulsions using a process known as membrane emulsification. A vertical oscillating membrane system was used to carry out drop formation experiments. It is shown that drop size can be tuned between 35 and 85 µm by changing just the surfactant concentration in the continuous phase. In addition, a method to determine the percentage of active pores during the membrane emulsification process is demonstrated. This method links knowledge acquired in the surfactant adsorption dynamics and drop expansion rate. Using this approach, pore velocity can be determined, which will help in determining the boundary between dripping and jetting from a pore. This study reinforces the importance of dynamic interfacial tension which must be considered in process design, and modelling purposes, particularly in two liquid phase systems using membranes such as membrane emulsification.

It is shown that formation of water based droplets in an immiscible (i.e. oil) continuous phase can be achieved using a hydrophilic porous metal membrane without prior hydrophobic treatment of the membrane surface. This avoids the need for "health and safety approval" of typical hydrophobic treatments for the membrane, which often use chemicals incompatible with pharma or food applications. To investigate this, wetting experiments were carried out:sessile droplets were used to determine static contact angles and a rotating drum system was used to determine contact angles under dynamic conditions. In the latter case the three-phase contact line was observed between the rotating drum, water and the continuous phase used in the emulsification process; a surfactant was present in the continuous phase which, in this process, has a double function: to assist the wetting of the membrane by the continuous phase, and not the disperse phase, and to stabilize the droplets formed at the surface of the porous membrane during membrane emulsification. KeywordsMembrane surface, hydrophilic, water in oil emulsion, polyvinyl alcohol (PVA), droplets and contact angle 2