Synthesis, surface properties, aggregation behavior of oleyl ether sulfates and their application to liquid crystal emulsion

Abstract

Oleyl ether sulfates (OEnS) with different EO addition numbers (nEO = 3, 5, 7) were systematically explored from synthesis, structural identification, surface properties and aggregation behavior to their application in the preparation of emulsion, where the structures of the prepared OEnS were identified by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (1H NMR). By analyzing the krafft temperature and surface properties of OEnS, the results showed that the higher the EO number, the lower the krafft temperature and CMC, with OE7S krafft temperature below 0 °C and CMC reaching 0.018 mmol/L, while the adsorption performance decreased with increasing EO number. Transmission electron microscopy (TEM) and polarized optical microscopy (POM) were used to observe the aggregation behavior, while dynamic light scattering（DLS）could be used to analyze the size of aggregates and small angle X-ray scattering (SAXS) was used to characterize the liquid crystal structure. It was found that OEnS solutions with concentrations up to CMC or above could form micellar aggregates of large size and had a lamellar liquid crystal structure at high concentrations, with the layer spacing increasing with the amount of EO. By studying the effect of OEnS on the formation of liquid crystal structures in emulsion, it was found that the higher the EO addition number, the smaller the size of the emulsified particles and the denser the lamellar gel network phase structure formed, combined with the study of rheological properties to prove that the emulsion had good storage stability and shear thinning properties.