I want to extend application scope of ceramic membrane in nonaqueous solutions. I wonder that is there exsit stable water-in-oil emulsions (W/O) without surfactant for experiment.
Please read this article: Effects of temperature on water-in-oil emulsions stabilised solely by wax microparticles.
Maybe it'll help. Best regards.
General answer is no. Any normal emulsion except a special type of microemulsions is unstable. In other words, thermodynamics drives emulsions destabilisation and phase separation (ISO TR 13097). But degree of destabilization is depending on time and stability criteria. So, kinetic stability may be o.k. in dependence on application. Beside the above ISO you may refer to our paper in J. Dispersion Science and Technology.2011, 32, 1799-1811, where some of our experince was summarized.
Water-In-Oil emulsions (crude natural oil) are extremally stable, in the case Resins are present, even more in Asphaltenic Oils. Resins and Asphaltens act as the Natural Surfactants, being adsorbed at Oil-Water Interface. The polar parts are located within the water droplets, non-polar parts of these surfactants are located in the Oil Phase. When droplets are in close proximity to one another, non-polar parts overlap, giving rise to large Osmotic Repulsion Force, preventing coalesence, rendering Colloidal Stability.
The paper, calculating this Force is attached.
Hello, I agree with Lerche that emulsion can be kinetically stable. Without surfactant you can use nanoparticle (Pickering emulsion), polymer, gelling agent, Liquid crystal etc.
I agree with Alam and Lerche emulsions are thermodynamically unstable systems due to high interfacial area of the dispersed phase so to archive stability the dispersion phase separates to reduce the interfacial area and hence the free energy of the system.
This phase separation is delayed by using surfactants which form a barrier against coalescence and also lowering interfacial tension between oil and water which facilitates easy mixing of water and oil. In addition to surfactants, particle stabilized (Pickering) emulsions can be prepared and studies have shown that these types of emulsions show more stability than surfactant stabilized emulsions because the particles are irreversibly adsorbed at the o/w interface. However, you should know that even in the absence of coalescence, emulsions break down due to other processes such as Ostwald ripening hence leading to instability of emulsions.
Nengwen, what did you decide to do? Although there are no stable emulsions in terms of "everlasting" it is possible to achieve a solution which is quasi stable during some hours or days. Have you tried to put the oil+water mixture in an ultrasonic bath?
Water in Oil Emulsion is extremely stable, protected by natural surfactants, which are getting adsorbed on Oil - Water Interface. Look at the experimental part of the paper attached. Measurements were done in real time. See page 147, Figure 10.
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