【作者】 刘浩；

【导师】 王朝阳；

【作者基本信息】 华南理工大学 ， 材料学， 2014， 博士

【摘要】 由于天然高分子来源广泛，而且具有无毒、生物相容性、生物可降解性及可回收利用等性能，利用这些高分子来设计和制备新型胶体粒子，并进一步用于稳定Pickering乳液和制备相关功能材料是材料科学领域备受关注的一个研究方向。本课题以壳聚糖为主线，利用Pickering乳液为模板，制备几种基于壳聚糖的新型Pickering乳液及相应功能材料，并且探讨了这几种乳液的稳定机理以及相关功能材料的应用研究。本研究的创新点为：拓宽了Pickering乳液的胶体粒子乳化剂的选择范围，首次探讨了壳聚糖分子在稳定Pickering乳液方面的基理与应用。而且，我们进一步探索了pH可逆的Pickering乳液在制备功能材料以及这些材料在实际生活中的应用。这种利用天然聚电解质制备pH响应性的Pickering乳液或者其它基于壳聚糖的功能性材料，也为其它刺激响应性的乳化剂或乳液体系在绿色经济以及环保领域的应用提供了一种新思路。本课题的主要内容和结果如下：1.首次采用纯的未经任何化学改性的壳聚糖，通过简单的调节壳聚糖水溶液的pH值，制备了一种新型的、具有优异pH可逆性的Pickering乳液。壳聚糖分子链上带上大量的氨基，它是一种天然的弱电解质。在酸性条件下，壳聚糖分子以溶胶的形式存在。而在中性或碱性条件下，壳聚糖分子形成纳米粒子或絮状沉淀。在此条件下，不同分子量壳聚糖形成的这两种形式的胶体粒子，均可以稳定不同极性与粘度的油相。所形成的Pickering乳液能够至少经历5次破乳-乳化的过程，并且能够至少放置两个月以上时间。在壳聚糖水溶液中盐浓度低于400mmol/L时，增加盐浓度能够增加Pickering乳滴的粒径。2.首次利用壳聚糖稳定的Pickering乳液，利用其优异的pH可逆性，通过绿色循环乳液聚合制备硫醇-烯微球。在油相中溶解有一定量的硫醇和烯烃单体，通过紫外光引发Pickering乳液聚合制备壳聚糖/硫醇-烯微球。然后，将制备的微球在酸性条件下浸泡，用盐酸溶解掉微球表面的壳聚糖，得到硫醇-烯微球。然后回收溶解的壳聚糖分子，继续进行下一次乳液和微球制备。绿色循环乳液聚合甚少可以持续三次。利用此方法制备功能性微球，具有以下优点：（1）采用天然高分子为稳定剂，实现了废弃物（虾壳、蟹壳等）的再利用；（2）稳定乳液所需要的乳化剂量少（只需要万分之五）；（3）通过绿色循环乳液聚合多次制备功能性微球，不需要多次添加乳化剂，制备过程经济环保；（4）制备的微球在药物装载与释放领域具有一定的应用，展现出对布洛芬药物的控制释放；（5）乳液体系有一定的生物相容性，制备的微球具有较强的可降解性。可以根据实际需要制备生物相容或生物可降解性的微球。3.首次以壳聚糖胶体粒子稳定的高内相Pickering乳液为模板，制备纯的壳聚糖的多孔洞结构的支架材料。通过提高壳聚糖溶液的浓度，可以制备更高内相体积分数的Pickering乳液。以1.0wt%的壳聚糖稳定的80%的内相体积分数的高内相乳液为模板，然后利用戊二醛交联壳聚糖粒子，除去油水相后，就得到多孔支架材料。Chitosan-GLA多级孔洞材料的大孔尺寸约为15μm，而相互贯通的小孔大小约几微米。控制戊二醛与壳聚糖的质量比，可以调节所形成的支架材料的抗酸能力，以及对铜离子的吸附能力。通过向支架材料中引入更多的吸附位点或者提供更多吸附空间，都能够提高多孔材料的吸附能力。壳聚糖多孔材料对铜离子的吸附过程可以由Freundlich理论描述：吸附过程是非均质吸附，并且在高浓度的铜离子溶液中更容易吸附。壳聚糖多孔支架材料有良好的吸附可逆性，经历十次去吸附-吸附后，吸附能力保持原始吸附量的90.3%。采用Pickering乳液模板法制备纯的壳聚糖多孔支架材料的操作简单可控。而且，所制备的壳聚糖多孔材料在实际中有一定的应用。4.首次以壳聚糖为一种弱聚电解质改性剂，以壳聚糖改性的氧化石墨烯（CS/GO）复合粒子为胶体粒子稳定剂制备新型Pickering乳液。当壳聚糖与GO质量比在0.0625-0.25区间时，CS/GO复合粒子能够稳定不同极性与粘度的油相。而且，无论是芳香族油相，还是脂肪族油相，在上述质量比区间产生的CS/GO复合粒子均能够形成稳定的水包油的Pickering乳液，这些乳液至少可以稳定2个月。说明了壳聚糖分子不仅能够单独的作为一种胶体粒子稳定剂，而且能够作为一种聚电解质改性剂改性粒子去制备有效的胶体粒子稳定剂，进而用于稳定Pickering乳液。5.首次以Pickering乳液为模板，通过层层（LbL）自组装法制备纳米复合的天然聚电解质微胶囊。采用聚醚酰亚胺（PEI）改性Laponite粒子，以PEI/Laponite复合粒子为胶体粒子制备Pickering乳液，制备的乳液可以至少稳定2个月，并且乳滴表面带有足量的正电荷。以此乳滴为模板，在其表面依次吸附海藻酸和壳聚糖天然聚电解质。吸附一定层数的聚电解质后，溶解掉内部的油相，得到中空的(海藻酸-壳聚糖)n微胶囊。本方法制备天然聚电解质微胶囊的优点：（1）相比传统的乳液，Pickering乳液模板具有更强的稳定性，能够有效防止自组装过程中，乳滴或聚电解质的团聚；（2）能够同时在微胶囊的壳层及内部的油相中装载有水溶性或油溶性的药物。我们向中空微胶囊中装载一定量的布洛芬，这种微胶囊对布洛芬的释放显示一定的缓释作用；（3）为制备其它微胶囊或功能性材料提供新思路。更多还原

【Abstract】 Because the excellent properties of nontoxicity, biocompatibility, biodegradability andrecoverability of natural polymers, there are growing interests in design and preparation ofnovel natural polymers-based colloid particles to stabilize Pickering emulsions, and fabricaterelated functional materials. For the first time, this study discusses the stability mechanism ofPickering emulsions stabilized by pure chitosan nanoparticles (CNPs) or other colloidparticles modified by chitosan. Based on these emulsions, this thesis describes thedevelopment of new strategies for the preparation of hierarchical macroporous material ordegradable polymer microspheres, and studies the practical application of these materials. Theinnovative ideas of this study can be concluded as follows: we develop novel kinds ofparticulate emulsifiers to stabilize Pickering emulsions; the proposed approach for preparationof various functional materials based on Pickering emulsion stabilized by pH-responsivechitosan expands the application of a wide range of reversible emulsifiers or emulsionsystems, and has a potential application in green economy or environmental protection. Themain contents and results of this study are listed as follows:1. For the first time, a simple reversible Pickering emulsion system stabilized by pureCNPs without any hydrophobic modification is developed. Chitosan has a pH-tunable sol-geltransition due to free amino groups along its backbone. At pH6.0, chitosan is insoluble inwater. CNPs or micrometer-sized floccular precipitates are formed in situ. These chitosanaggregates can adsorb at the interface of oil and water to stabilize O/W Pickering emulsions.At pH6.0, chitosan is soluble in water. Demulsification happens. Four organic solvents(liquid paraffin, n-hexane, toluene, and dichloromethane) are chosen as the oil phase.Reversible emulsions are formed for all four oils. Chitosan-based Pickering emulsions canundergo five cycles of emulsification-demulsification with only a slight increase in theemulsion droplet size. They also have good long-term stability for more than2months. Whenthe salt concentration of chitosan aqueous solution is less than400mmol/L, the droplet size ofPickering emulsion increases with increasing of salt concentration.2. Pickering emulsion stabilized by pH-reversible chitosan is developed to preparedegradable polymer microspheres by emulsion photopolymerization, where chitosan acts as a green and recyclable particulate emulsifier. The thiol-ene photopolymerization oftrimethylolpropane tris(3-mercaptopropionate) and trimethylolpropane triacrylate is initiatedby UV irradiation. The property of excellent pH-reversibility of chitosan endows it to be usedfor recycles in emulsion polymerization at least three times. Pure microspheres are obtainedby dissolving the chitosan-coated microspheres in HCl aqueous solution to remove chitosan.Ibuprofen is loaded into the microspheres. The higher release temperature or pH value, thefaster release rate and higher release extent of IBU from the microspheres are found.Meanwhile, the resulting microspheres exhibit a good degradability in1M NaOH aqueoussolution, with a weight loss of about90wt%after35days. This study opens up a new routefor the green and recyclable application of chitosan in fabrication of degradable polymermicrospheres.3. Chitosan scaffolds with hierarchical macroporous structures for recyclable adsorptionof Cu2+are prepared by templating from Pickering high internal phase emulsions (HIPEs) forthe first time. The liquid paraffin-in-water HIPEs are stabilized by CNPs. The internal phasefraction can be up to90.0%, meanwhile the chitosan concentration only needs1.0wt%. Thechitosan scaffolds are obtained by crosslinking the dispersed CNPs, followed by removing theinternal phase. The resulting scaffold exhibits the average pore size of around15m andinterconnecting throat size of several micrometers. The adsorption capacities of thechitosan-glutaraldehyde (chitosan-GLA) scaffolds for Cu2+increase with increasing the molarratio of-NH2of CNPs to-CHO of GLA. At the optimized ratio of2:1, the adsorption capacityis60.2mg/g at room temperature and pH5.0. The adsorption capacity can be greatlyimproved by addition of carboxymethylated chitosan or adopting imprinting method, and theadsorption capacities are100.2,90.3mg/g, respectively. The adsorption isotherm of thechitosan scaffold closely follows Freundlich model. Furthermore, the adsorption capacity ofthe scaffold undergoing10consecutive desorption-adsorption cycles still maintains at a highlevel of90.3%, suggesting the chitosan scaffold is a green and recyclable biosorbent inpractical wastewater treatment.4. For the first time, chitosan acts as a new kind of weak polyelectrolyte modifier tomodify graphene oxide (GO), and Pickering emulsions are stabilized by the CS/GOnanocomposite colloid particles. When the mass ratio of chitosan and GO is in the range of 0.0625-0.25, no matter what the polarity and viscosity of oils are, besides, whatever the oilsare aromatic solvents or aliphatic solvents, the obtained CS/GO colloid particles can stabilizePickering eumulions, which have good long-term stability for more than two months. Thisstudy suggests that chitosan molecules can not only act as an effective particulate emulsifierto stabilize Pickering emulsions alone, but also as a kind of modifier to preparenanocomposite colloid particles with other particles, and preparation of Pickering emulsions.5. Nanocomposite polysaccharide microcapsules composed of biocompatiblepolyelectrolyte complex via electrostatic Layer-by-Layer self-assembly on Pickeringemulsions template method are firstly prepared. PEI/Laponite-based Pickering emulsions areobtained regardless of the polarity and viscosity of the oils at PEI/Laponite mass ratio of0.5and Laponite concentration of0.25wt%, and these emulsions show good long-term stabilityfor more than two months. Four bilayers sodium alginate-chitosan microcapsules with thedimension of about43.9μm and wall thickness of55nm were prepared by alternateadsorption of negatively charged alginate and positively charged chitosan on Pickeringemulsions. Hollow microcapsules are obtained after core removal at a mild condition ofwashing with excess2-propanol. IBU as a model drug is loaded into hollow microcapsules,and the release rate of IBU from the microcapsules at pH7.4is obviously faster than therelease rate at pH2.0. The more polyelectrolyte layers of IBU-loaded microcapsules, the moredifficult for IBU release.更多还原