【作者】 乔俊强；

【导师】 冯博学； Diethelm Johannsmann；

【作者基本信息】 兰州大学 ， 材料物理与化学， 2012， 博士

【摘要】 本论文中首先介绍了通过微乳液法制备聚甲基丙烯酸甲酯[Poly(Methyl methacrylate), PMMA]与甲基丙烯酸甲酯—乙酸正丁酯共聚物[Poly(methyl methacrylate-n-butyl acrylate), P(MMA-BA)]的微乳液分散体系,测量了体系中胶体粒子的尺寸分布(rD-65nm)。通过改变单体组分中乙酸正丁酯含量,考察其对临界裂纹厚度的影响,并研究其制备薄膜的成型性。同时,利用显微镜观察薄膜表面形貌。结果表明,单体中乙酸正丁酯含量在改变聚合物玻璃化转变温度后,可影响聚合物薄膜材料塑性、韧性及硬度,进而提高材料的成膜质量；其次,研究了天然纳米管材料——埃洛石纳米管(Halloysite nanotube, HNT)的性能,以及在聚合物微乳液中掺杂HNT对聚甲基丙烯酸甲酯(PMMA)与甲基丙烯酸甲酯—乙酸正丁酯共聚物[P(MMA-BA)]的增强作用,试验研究了HNT/PMMA、 HNT/P(MMA-BA)复合材料的成膜性,考察了纳米复合高分子薄膜材料的力学及热力学等性能,利用偏光显微镜观察薄膜中的微结构,分析聚合物在成膜过程中的应力分布,并通过AFM、SEM、摆杆阻尼硬度分析等测试手段研究了埃洛石纳米管加入前后高分子薄膜的微观结构形态与性能的变化。结果表明,HNT与基体聚合物材料结合紧密,可有效改善制膜材料的性能,TGA测试表明其热力学性能也得到大幅度提高。当聚合物与HNT固体含量比为1：1-1.2时,薄膜质量最佳,HNT的增强效果最为显著,纳米复合材料所制薄膜的临界裂纹厚度较纯聚合物薄膜可增加约400%。与此同时,通过尝试不同实验条件,探索改善纳米管增强相在在胶乳液中的分散的方法,采用不同强度搅拌、高强度超声、长时间循环振动等方法对聚合物微乳液中HNT分散相进行预处理,并采用聚乙二醇(Polyethylene glycol, PEG1500)作为辅助分散剂,通过DLS研究了不同分散条件对埃洛石纳米管分散相均匀化的作用,最终确定最佳实验条件,并考察对HNT分散体系进行预处理后对纳米复合材料成膜性能的改善；最后,在制备出具有良好性能纳米复合薄膜材料的基础上,考察其作为涂层材料的性能指标,分析表明,纳米复合薄膜的力学性能较未掺杂增强相之前有较大改善。通过Fick扩散定律与Lucas-Washburn模型分析,并设计实验测试其耐湿性能,得到了纳米复合薄膜的吸湿过程曲线、饱和相对湿度,通过测定其吸湿量发现,随着埃洛石纳米管分散相含量的提高,由于纳米材料所具有的大比表面积,润湿有所增强,平衡吸水率随之增加,但由于基体和增强相的疏水性质以及薄膜内部的毛细管作用,尽管其微观形貌表现出一定的多孔特征,其吸湿速率呈现出两阶段不同趋势。在起始阶段,随着HNT含量的增加,吸温速率随之减小；在第二阶段,在起始阶段达到一定吸湿量后,吸湿速率开始呈现明显下降的趋势,表现出良好的耐湿性能。更多还原

【Abstract】 This work is mainly concentrated on the film formation from polymer latex which is polymerized from microemulsion, Halloysite nanotube (HNT)/Polymer latex dispersions and the evaluation of the improvement, such as mechanical and thermal properties of the films. The first major topic is the development of methods for solving the cracking problem in latex films. The second important part is the evaluation of the nanocomposite films which are after different way of treatment and of improved properties.Commonly, there is a quandary in polymer film formation:soft polymer particles are needed for preventing films cracking when deform but hard films are expected afterwards for good mechanical properties. It was found that the intermixed layer between two Poly(Methyl methacrylate)(PMMA) particles, widened by increasing the drying temperature, would be helpful for preventing cracking even there are always stress fluctuations in drying polymer dispersions which easily cause the micro crack. The addition of n-Butyl acrylate (BA) is proposed as a method to decrease the hardness but to increase the critical cracking thickness of PMMA latex films. Our results show that the softer P(MMA-BA) latex particles of lower Tg lead to higher critical cracking thicknesses.Another method developed, different from adjusting the forming temperature and hardness of polymer by copolymer to improve the film formation, is the introduction of the Halloysite nanotube (HNT) which could naturally bridge the polymer particles together and form a physical cohesive connection between them. As showed in experiments, the intercalation of organic compounds would be favored when halloysite is hydrated. Theoretically HNTs can both sustain the stress of deformation based on and aid the concomitant interdiffusion of polymer particles during drying, resulted in higher critical thicknesses (up to nearly400%as higher). Thick, crack-free films were made from hard latex. It was found that the dispersion of HNT has a significant effect on the film formation from polymer latex. But here comes a problem. Halloysite nanotube, directly manufactured from the natural minerals and often hard to be refined during processing, will therefore be of a large range of size distribution in micro-scale and burden the polymer-HNT nanocomposites with the nanotube aggregation most of the time. From the observation by microscope, it can be concluded that even applied into the polymer latex which is much more viscous than water, Brownian motion still has a significant effect on the HNT dispersion in the latex. Stirring, high shear mixing, sonication and shaking pre-treatment of HNT suspensions with the help of the coagulant Polyethylene glycol (PEG1500) can sorting the HNTs and make them homogeneously disperse in the latex, and then improve the polymer films’properties at the end. Meanwhile, although after proper treatment, HNTs will still have the trend to cluster together in suspensions because of the strong Van der Waals interaction between tubes and their high specific surface area. As the experiments show that increasing the HNT content can help to decrease the cracking in HNT/PMMA and HNT/P(MMA-BA) nanocomposite films, in order to improve the surface quality of the films, it would be better to decrease the HNT bundles than simply lower the Halloysite content.At last, the nanocomposite films from the latex dispersions mixed with HNT are very white. This can make the materials a candidate of painting without Titania. In the moisture absorption test, polymer films show an increasing water mass fraction in equilibrium with the HNTs. This can also explain to some extent the strengthen mechanism, that is, Halloysite slower the drying of films to supply enough time for the deformation and alleviation of the strain during film formation. And interestingly, with the increasing solid content of HNT, films absorbing water become slower which represent a good moisture resistance.更多还原