Phase transitions in O/W lauryl acrylate emulsions during phase inversion, studied by light microscopy and cryo-TEM

Phase changes during the preparation of nano-emulsions containing polymerizable monomer as the oil phase, by the phase inversion temperature technique (PIT), were investigated using light microscopy, cryo-TEM and viscosity measurements. The nano-emulsions were prepared using a poly(oxyethylene) nonionic surfactant and a polymerizable acrylic monomer (lauryl acrylate) as the oil phase. Inversion of the emulsion, followed by rapid cooling, resulted in emulsions having an average droplet size as low as 25 nm. Cryo-TEM was used to observe the structures that are present above and below the phase transition temperature, and gave, for the first time, visual indication of the presence of a microemulsion and a locally ordered structure in the process. At high surfactant concentrations, the inversion-cooling process yields emulsions with unique structures, in which the oil phase is present as worm-like structures.