Emulsions Stabilized By HMHEC, HMHEC/Laponite And HMHEC/Surfactants

The use of polymeric surfactants as emulsifiers and stabilizers in emulsions has attracted much attention in recent years. Among the polymeric surfactants, hydrophobically modified water-soluble polymers have been a target of extensive studies because of their potential industrial applications, such as water-borne paints, coating fluids, cosmetics, foodstuff, drug delivery systems, enhanced oil recovery and water treatment and also because of their relevance to biological macromolecular systems. This kind of polymer is a water-soluble polymer with a few hydrophobic groups in the hydrophilic macromolecular chain. They can lower the surface and interfacial tension due to their intrinsic amphiphilic properties, though their abilities are much lower than those of the conventional low-molecular-weight surfactants. However, their solutions showed much better thickening ability than low-molecular-weight surfactants solutions due to their large molecular structures and the association of the hydrophobic groups on the backbone. Hence, the emulsification mechanisms differ from those of the low-molecular-weight surfactants. This kind of polymer can also have strong interaction with solid particles and small surfactants forming complex to stabilize emulsions. Hydrophobically modified hydroxyethyl cellulose (HMHEC) is choosed as main study subject in this paper. Effect of HMHEC, HMHEC/Laponite and HMHEC/surfactants on the stability of emulsions is systematically investigated. The variation discipline of emulsions stability and emulsion stabilization mechanism are proposed. All of the results are of theoretical and practical meanings to the study of the emulsions prepared by this kind of polymer. This paper could be divided into three parts as follows:1. Emulsions stabilized solely by HMHECThe properties of aqueous HMHEC soultins and oil-in-water emulsions prepared by HMHEC are systematically studied by interfacial tension, rheological measurement, laser scattering, ESEM (environmental scanningelectron microscope) and TOC.Due to the hydrophobic groups on the backbone, HMHEC can adsorb at the oil/water interface and lower the interfacial tension of the HMHEC/water/oil system, which affords the emulsification conditions. Intra-molecular association behavior is dominative when the concentration of HMHEC is lower and the viscosity of aqueous HMHEC solutions is very low. The viscosity of aqueous HMHEC solutions increases sharply when HMHEC concentrations reach a critical value (0.6 wt% in this experiment). Cloud point results incicats that HMHEC have strong salt resistence. The viscosity of aqueous HMHEC solutions has important influence on the emulsion stability, and a three dimensional network will form in the system at a higher HMHEC concentration. Emulsion droplets can be traped in the mesh of the network and their sedimentation rates are lowered, leading to the increase of emulsion creaming stability.The results of optical microscope and laser scattering incicate that the emulsion droplets size decreases with increasing HMHEC concentrations, and size distributions of emulsions go well-proportioned.Environmental Scanning Electron Microscope (ESEM) technology was first used to observe the surface topography of emulsion droplets and the adsorption of HMHEC at the curve surface of the emulsion droplets. The results show that HMHEC can be adsorbed at the oil-water interface through the penetration of the alkyl chains on HMHEC into the oil phase and form a firm polymer layer. This polymer layer is just like a "tough skin" around the emulsion droplets and can enhance the emulsion stability to coalescence.The experiments of emulsios salt resistence show that salt could not produce visible effect on the stability of emulsions.2. Emulsions stabilized by HMHEC/Laponite mixed dispersionsThe interaction between HMHEC and Laponite and the effect of HMHEC/Laponite mixed dispersions on the emulsion stability are investigated in this part.HMHEC can affect the dispersed state of Laponite particles. HMHEC can adsorb at the surface of Laponite particles and lower the Laponite zeta potential to make them flocculate. The flocculation stage will increase with increasing the concentration of HMHEC and Laponite particles. Gel with high strength will form by the bridge interaction between particles due to the association of HMHEC when the concentration of HMHEC and Laponite particles reach a higher level.Oil-in-water emulsions were successfully prepared by adjusting all kinds of factors such as particles concentrations, polymer concentrations and the oil volume fraction. Stability of emulsions increased and emulsion droplet size decreased with increasing Laponite particles concentrations at the same oil volume fraction and polymer concentration. Stability of emulsions also increased with oil volume fraction at the same particles and polymer concentrations, only the droplets size get larger.Viscosity of HMHEC/Laponite aqueous dispersion increased with increasing HMHEC concentration and a three dimensional gel-like net-work will form in given conditions. This net-work can effectively enhance the creaming stability of the emulsion and trap the emulsion droplets in the mesh to increase the coalescence stability of emulsions. The complex particles in HMHEC/Laponite mix dispersion can adsorb at the surface of emulsion droplets which can great enhance the coalescence stability of emulsions.3. Emulsions stabilized by HMHEC/Surfactants systemInteraction between HMHEC and SDS, CTAB were studied by several methods. Emulsions stabilized by HMHEC/SDS and HMHEC/CTAB systems were prepared and the effect of several influencing fator to the stability of emulsion was studied. HMHEC has strong interaction with surfactants in aqueous solutions. The viscosity of HMHEC/Surfactants solutions first increased and then decreased with increasing surfactant concentrations, corresponding to the classic rule of interaction between hydrophobically associating polymer and surfactants.HMHEC/Surfactants solutions have a stronger ability to lower the oil/water interfacial tension compared with HMHEC solutions, which make the emulsification process easier. The droplet size of emulsions prepared by HMHEC/Srufactant solutions decreased with increasing surfactant concentrations.The stability of emulsions prepared by HMHEC/Srufactants solutions is much higher than that prepared solely by surfactant solutions. Due to the large difference between the HLB value of surfactants and oil and the poor thickening ability of surfactants, the stability of emulsions prepared solely by surfactants is a little poorer.