| Chitosan( CS) is widespread in nature as the only kind of alkaline polysaccharide, with good biochemical properties such as biocompatibility, biodegradable, non-toxic, and good physical and chemical properties such as hygroscopicity, moisture resistance, and antimicrobial properties. In this thesis, PS particles were modified by CS and two kinds of CS based Pickering emulsion were investigated. The adoption of CS instead of surfactants and some synthetic polymers used in other studies may reduce skin irritation and toxicity, and endow some special features to the prepared Pickering emulsion at the same time. On the other hand, problems of triviality, poor sphericity and nonuniform size distribution in the preparation of core-shell composite particle were solved by a simple template method.Firstly, polystyrene(PS) particles were in-situ modified by CS through electrostatic interaction, and applied as Pickering emulsion stabilizers with liquid paraffin as oil. The obtained Pickering emulsions were characterized by optical microscope, SEM and fluorescence microscope. Effects of the concentration of PS particle and CS, water to oil ratio,dispersion p H and salt concentration on the properties of Pickering emulsion were investigated. The results indicated that emulsions were most stable at condition where particles were most flocculated, and Pickering emulsion with internal volume fraction as high as 85% was obtained. In addition, the mechanism of the emulsification of PS particles in-situ modified by CS was proposed by studying the adsorption of CS on PS particles and flocculation of PS particles. Specifically, synergistic interaction between PS particles and CS occurred with deficit CS, that is, addition of CS into PS particles promoted the flocculation of particles and the accompanyingemulsifying capacity, whereas competitive interaction occurred with excess CS, namely the adsorption of PS particles at the interface was inhibited by excess CS and the emulsion was mainly stabilized by CS. Meanwhile, the fact that there was no phase inversion was caused by the increasing hydrophilicity of particles after adsorbing CS.Secondly, a core-shell PS/CS composite particle with uniform particle size of 250 nm was fabricated through a simple template method with glutaraldehyde as crosslinker,according to the characterization of FTIR, Zeta potential, SEM and TEM. The optimized concentration of glutaraldehyde, temperature and time of the cross-link reaction was 15.96mmol/L, 40 °C and 24 h, respectively. The emulsifying ability of the composite particle was investigated by discussing the effect of particles concentration, water to oil ratio, dispersion p H and salt concentration, with liquid paraffin as oil. In comparison with PS particle, the emulsifying ability of the core-shell particle was greatly improved, and the emulsion had a long-term stability with only 1 wt% particles. High internal phase Pickering emulsion was also obtained, with an internal volume fraction of 85%. What’s more, it is discovered that emulsifying ability of the composite particle wasn’t influenced by salt concentration or p H,probably because of the reduction of amino amount, and even at acidic condition, the emulsion could be stable as long as 1 year.Finally, the antibacterial activity of the PS particles modified by CS was investigated against Escherichia coli(E.col) and Staphylococcus aureus(S.au), as well as the CS based Pickering emulsion. The complex of PS particles and CS showed excellent antibacterial activity, and this antibacterial activity was improved by increasing CS concentration in the complex. The minimum inhibitory concentration(MIC) of Pickering emulsion stabilized by 3wt% PS particles and 0.08 wt% CS relative to oil(the volume ratio of water to oil was 3:7)was 40 wt% both against E.col and S.au. However, it is unexpected that indistinctive antibacterial activity of cross-linked core-shell PS/CS particle was demonstrated, which could be ascribed to the reduction of amino amount. |
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