Oil-in-water emulsions stabilized by hydrophobically modified hydroxyethyl cellulose: Adsorption and thickening effect

The preparation and stability of oil-in-water emulsions stabilized by hydrophobically modified hydroxyethyl cellulose (HMHEC) were investigated. The rheological measurements of aqueous HMHEC were studied. It was found that HMHEC showed much better thickening ability than the parent (HEC) from which it was derived, which is caused by the association of the hydrophobic alkyl chains, which are absent in HEC. The oscillatory experimental results of the emulsions showed that at higher concentrations, HMHEC could form an elastic gel, which has good thixotropic properties. The stability and droplet size distribution were investigated by visual observation, photomicrograph and a laser-scattering particle size distribution analyzer. The adsorption of HMHEC at the oil–water interface and the surface of emulsion droplets due to the penetration of the alkyl chains in HMHEC into the oil phase were confirmed by visual observation, the interfacial tension method and an in situ environmental scanning electron microscope (ESEM). The stability of emulsions prepared using HMHEC is based on both an associative thickening mechanism caused by alkyl chains in HMHEC and the adsorption of HMHEC at the oil–water interface, which can form a solid film preventing coalescence of the droplets.

ESEM image of emulsion prepared with HMHEC with a concentration of 1.0 wt%, the magnification factor is 6000×. The ESEM image clearly shows the adsorption of HMHEC at the surface of the emulsion droplets. This is a key factor for the emulsion stability.Figure optionsDownload as PowerPoint slide