Surfactant-mediated water transport at gelatin gel/oil interfaces

We studied spontaneous emulsification (SE) at Water/Oil (W/O) interfaces, using several types of aqueous reservoirs immersed in dodecane plus Span80 surfactant. Above a threshold surfactant concentration CSE, aqueous satellite droplets are formed at the W/O interface. Varying the aqueous reservoir size, from below 100 μm (droplets) to centimeters (macroscopic phases), allowed investigating SE with complementary techniques. Release (rates) and size distributions for SE droplets were measured with microscopy. For gelled aqueous phases, water expulsion due to SE was quantified. Values for CSE were measured and were found to be higher for aqueous phases containing gelatin and/or NaCl. We also studied water exudation during network building and syneresis in aqueous gelatin gels immersed in dodecane/Span80. Below CSE (i.e., in the absence of SE) this process is still responsible for significant physico-chemical changes at the W/O interface. To study these in more detail, we performed atomic force microscopy experiments (in force–distance mode) on macroscopic gels. Both changes in the local elastic response and in the wettability of the AFM tip were detected. Together they suggest the formation of “water pockets” after prolonged (gel) setting times, along with a densification of the interfacial gelatin network.