The effect of incorporation of different hydrophobic pluronics on the evolution of liquid crystalline structures in a nonionic microemulsion.
Abstract
This research article describes water-driven phase changes in a microemulsion composed of TPGS-Capryol 90 as a surfactant mixture and clove oil as an oil phase. After optimizing the surfactant mixture, Pluronics® of different hydrophobicity (L121, P123, and P105) were incorporated into Smix at a fixed concentration for delineating their effects on the formation of liquid crystalline (LC) structures. Characterization studies were performed along a water dilution line constructed within the monophasic region. The data were obtained using polarised light microscopy (PLM), small-angle X-ray scattering (SAXS) and rheology experiments. We recorded a progressive transformation of the microemulsion into lamellar LC structures upon increasing the water content from 20 to 40%. SAXS data showed well-defined peaks corresponding to lamellar ordering. The effect of Pluronics® could be noticed in the inter-lamellar spacing, which followed the order: P123 > P105 > L121. While comparing the data obtained at an identical water level, we found that hydrophobic L121 favoured the formation of tightly packed and weakly hydrated lamellae. Relatively hydrophilic Pluronics® (P123 and P105) produced swollen ones. This interpretation was further supported by rheological analyses, which showed that LC structures carrying L121 could resist shear to a higher degree. In contrast, structures formed with P123 and P105 appeared to be deformable. Collectively, these results underscore the potential utility of triblock copolymers for tuning the mechanical and viscoelastic properties of mesophasic structures.