【作者】 张建安；

【导师】 葛学武；

【作者基本信息】 中国科学技术大学 ， 高分子化学与物理， 2011， 博士

【摘要】 近年来,由于无机/聚合物复合(微球)材料可以用做涂料、阻燃材料、光阻材料、活性物质载体、催化材料及光学器件等,吸引了学术界和工业界的广泛关注。在这类复合材料中,惰性的聚合物是一种理想的载体,既有利于活性物质的接触,又有利于材料的回收和重复使用；而无机组分的引入不仅提高了聚合物复合材料的力学性能,同时也赋予了复合材料以功能性。复合微球的形貌是影响其功能性的一个重要因素,不同的形貌结构具有不同的功能性和应用领域。例如,单分散微球自组装可以形成三维有序胶体晶体,用于制备光子晶体和作为多孔材料的模板,但目前单分散微球的自组装方法有待进一步开发,自组装工艺、胶体晶体膜强度也有待进一步的完善。中空型微球可以作为载体,实现活性物质的包封和控制释放,如何有效制备和精细控制中空结构仍需要深入研究。非球形微球具有与球形微球不同的堆积类型,可用于改善材料的光学性能,形成生物材料的自组装构造单元,调控悬浮液的流变性能和设计新型复合材料等。目前对非球形聚合物微球的制备方法、形成机理以及微球形貌的可控性都有待深入研究。金属/聚合物复合微球可以发挥纳米金属粒子的功能性,但如何对聚合物微球进行表面修饰以满足纳米粒子和聚合物载体的有效复合也需要进一步的研究。本论文即围绕着上述几类无机/聚合物复合材料的制备和微球的形貌控制,依次开展了多重Pickering乳液模板法制备无机/聚合物中空微球的研究；细乳液聚合法制备SiO2/P(MMA-co-St)非球形复合微球的研究；双原位细乳液聚合法制备SiO2/聚合物纳米复合微球的合成、性能及其形貌控制的研究：Janus型无机/聚合物复合微球的设计与合成；采用两步分散聚合法制备银/聚合物复合微球的研究；单分散聚合物微球的无皂乳液聚合法合成、自组装及以其为模板制备多孔材料的研究。主要有如下七个方面的研究成果：(1)用表面改性的双亲性SiO2纳米粒子作为Pickering乳化剂制备W/O/W型乳液；以此多重乳液为模板,引发中间油相的单体聚合,一步制备中空微球。此方法中,首先制备W/O型乳液,在碱性条件下,正硅酸乙酯(TEOS)在油/水界面原位水解生成SiO2纳米粒子,接着在油/水界面被Y-甲基丙烯酰氧丙基三甲氧基硅烷(MPS)部分改性得到双亲性SiO2纳米粒子。在此体系中再加入外水相,利用双亲性SiO2纳米粒子作为Pickering乳化剂,得到稳定的多重乳液。中间的油相单体苯乙烯(St)聚合后,可一步得到中空微球。表面改性时间影响SiO2粒子的大小和最终中空微球的壁厚；MPS的用量和油/水体积比影响SiO2纳米粒子的表面改性效果。(2)采用种子细乳液聚合方法,以MPS为功能单体,MMA为单体,TEOS为SiO2粒子的前驱体,首先得到SiO2纳米粒子交联的SiO2/PMMA种子微球。继续滴加第二种单体St聚合,得到非球形SiO2/聚合物复合微球。结果表明,交联剂的用量和种类对微球的形貌影响很大。若不加MPS,SiO2/PMMA种子微球没有交联,复合微球呈核壳结构；而加入MPS后,SiO2/PMMA种子微球被SiO2纳米粒子交联,种子微球上出现多个聚苯乙烯鼓包,复合微球呈梅花状结构；若再加入另外一种交联剂DVB,复合微球呈花生状。(3)以十二烷基硫酸钠(SDS)为乳化剂,正十六烷(HD)为助稳定剂,MMA、丙烯酸丁酯(BA)为聚合单体,TEOS为前驱体通过双原位细乳液聚合法制备了SiO2/聚(甲基丙烯酸甲酯-丙烯酸丁酯)复合微球。结果表明,复合微球呈树莓状,原位生成的SiO2纳米粒子位于其壳层,大小约20nm,均匀分散在聚合物基质中,彼此之间没有团聚。聚合物纳米复合物薄膜的透光率在400-800nm范围内为70-80%左右,与纯聚合物薄膜相当。SiO2纳米粒子的引入,提高了聚合物的机械性能,并且改善了阻燃性能。(4)采用双原位细乳液聚合方法合成了Janus结构的复合微球。研究发现,形成Janus型复合微球的关键是水溶性引发剂的使用。这样,在水中形成的初级自由基,扩散到细乳液液滴的界面,从而在界面处引发单体聚合,并促使TEOS和聚合物之间发生相分离。此时在碱性催化剂作用下TEOS发生水解缩合反应生成SiO2,即可得到一半为PS、另一半为SiO2的Janus复合微球。(5)以MMA为单体,以TEOS为SiO2粒子的前驱体,以MPS为改性剂,采用双原位细乳液聚合方法,使单体的聚合反应和TEOS水解缩合生成SiO2粒子的反应同时进行,一步制备出不同形貌结构的SiO2/聚合物微球。研究发现,乳化剂的用量影响聚合反应体系的稳定性和复合微球的形貌结构。在适宜的SDS用量下,MPS的用量影响着相分离的过程和最终复合微球的形貌结构。高MPS含量时,得到中空结构的复合微球,SiO2纳米粒子分布在微球的壳层；低MPS含量时,得到的复合微球呈“碗”状结构,聚合物构成了“碗”的底部。(6)提出了一种合成纳米Ag/PS复合微球的简单方法。首先以苯乙烯、衣康酸和丙烯腈为单体,以乙醇/水为反应介质,制备出表面含有羧基和氰基的PS微球。再将AgNO3水溶液滴入到上述制备的PS微球分散液中。银离子被静电吸附到微球表面,接着被加入的水合肼原位还原成约50nm的银粒子,得到纳米Ag/PS复合微球。结果表明,与未加丙烯腈单体相比,微球表面引入的氰基提高了银粒子在微球表面的附着能力。制备的纳米Ag/PS复合微球具有良好的催化性能。(7)采用无皂乳液聚合法合成出单分散性的PS微球,通过漂浮自组装法制备了自支撑胶体晶体膜,进而以此为模板制备了多孔材料。研究发现,以乙醇/水混合物为分散介质,可以降低微球自组装的温度,能够在15min内得到三维有序结构的胶体晶体。以环氧氯丙烷为交联剂,可得到自支撑的胶体晶体膜。以此胶体晶体为模板,采用渗透法填充前驱液Ti(i-OPr)4,制备了骨架为棒状结构的三维有序TiO2多孔材料。更多还原

【Abstract】 In recent years, inorganic/polymer nanocomposites (microspheres) have attracted extensive academic and industrial attention because of their applications in coating materials, fire-retardant materials, photoresist materials, catalytic materials, optical devices, etc. In the inorganic/polymer nanocomposites, polymer component acts as an ideal carrier which is easy access to active substances and favors the recovery and reultilization of materials. The introduction of inorganic component not only improves the mechanical properties of polymer composites, but also imparts the functionality to composite materials. The morphology of composite particles plays an important role on their functionality. For example, monodisperse microspheres are the most studied and best established example as the self-assembling building blocks to successfully fabricate three dimensionally (3D) ordered colloidal crystals, which can be used as the removable templates to fabricate 3D macroporous materials. However, the self-assembly method need to be further developed and the colloidal crystals film need to be strengthened. Hollow nanostructural microspheres have giant commercial applications including encapsulation and controlled release of sensitive materials, such as drugs, cosmetics, DNA, energy storage and conversion, and catalysis. However, the feasibility of preparation and control of hollow microspheres deserve further investigation. The stacking types of nonspherical particles are different from those of spherical particles so that nonspherical particles can be used to improve the optical properties of materials, act as self-assembly blocks for biological structural materials, control the rheological properties of suspensions, and design composite materials. Although the synthesis of nonspherical inorganic nanoparticles has been widely studied, the preparation, formation mechanism, and morphology control of nonspherical polymer microspheres still deserve further study.A series of research work on the preparation and microsphere morphology control of the above mentioned inorganic/polymer composite materials have been carried out. We studied the synthesis of inorganic/polymer hollow microspheres templated from multiple Pickering emulsions; the preparation, morphology control, and properties of SiO2/polymer composite microspheres via double in situ miniemulsion polymerization; the design and synthesis of Janus inorganic/polymer composite microspheres via double in situ miniemulsion polymerization; the synthesis and properties of nano silver particles/polymer composite microspheres by a two-step dispersion polymerization; and the synthesis and self assembly of monodisperse polymer microspheres to prepare colloidal crystal and further porous materials. The main results on the seven aspects of the research work are as follows:(1) Stable W/O/W multiple emulsions were successfully prepared by using the in situ formed amphiphilic silica particles as the Pickering emulsifier. Inorganic/polymer hollow spheres were fabricated after the polymerization of interlayer oil monomers. The water-in-oil (W/O) emulsions were first prepared by using the mixture of styrene, tetraethoxysilane (TEOS), hexadecane, and y-(trimethoxysilyl) propyl methacrylate (MPS) as the oil phase, and aqueous triethylamine solution as the inner water phase, respectively. By the hydrolysis-condensation of TEOS under basic conditions, silica particles were formed and modified by MPS at the O/W interface. W/O/W emulsions were fabricated by adding water as the outer phase. Finally, hybrid hollow microspheres were obtained after the further polymerization of the interlayer phase. The results showed that the time of surface functionalization had great effects on the size of silica particles and then the wall thickness of hollow microspheres. The modification level of silica nanoparticles were influenced by the content of MPS and volume ration of W/O phase of the primary W/O emulsions.(2) The SiO2/polymer seed microspheres were fabricated via in situ miniemulsion polymerization of MMA using MPS as functional monomer and in situ hydrolysis-condensation reaction of TEOS under basic conditions, and non-spherical polymer particles were obtained after styrene monomer was added dropwise and initiated to polymerize. The results showed that the addition of crosslinking agent divinylbenzene (DVB) and the contents of SDS and MPS in the formulation have great effects on the morphology of microspheres. The hybrid microspheres have a core-shell structure without the use of MPS and turn into a plum-like structure in the presence of MPS. If both DVB and MPS were added, the microspheres showed a peanut-shaped morphology.(3) SiO2/polymer nanocomposite microspheres were prepared by double in situ miniemulsion polymerization in the presence of methyl methacrylate, butyl acrylate, MPS, and TEOS. By taking full advantage of phase separation between the growing polymer particles and TEOS, inorganic/polymer microspheres were fabricated successfully in a one-step process. The formation of SiO2 particles and the polymerization of organic monomers took place simultaneously. The results showed that nanocomposite microspheres had a raspberry-like structure with silica nanoparticles on the shells of polymer microspheres. The silica particles of about 20 nm were highly dispersed within the nanocomposite films without aggregations. The transmittance of nanocomposite film was comparable to that of the copolymer film at around 70-80% from 400 to 800 nm. The mechanical properties and the fire retardant behavior of the polymer matrix were improved by the incorporation of silica nanoparticles.(4) Inorganic/polymer Janus microspheres were fabricated successfully in a one-step process by miniemulsion polymerization. Our method involved the in situ miniemulsion polymerization of styrene and the in situ hydrolysis-condensation of TEOS under basic conditions. The use of water-soluble initiator plays a key role on the formation of Janus-type microspheres. Thus, the primary radicals form in the water medium, spread to the interface of miniemulsion droplets, and initiate the polymerization of monomer at the interface. With the phase separation between the growing polystyrene particles and TEOS, Janus microspheres consisting of a silica hemisphere and a polystyrene hemisphere were obtained. The Janus microspheres showed the amphiphilicity due to the different chemical composition of each hemisphere.(5) A facile and effective approach has been developed to prepare hybrid hollow/bowl-type SiO2/PMMA microspheres via the double in situ miniemulsion polymerization by taking full advantage of phase separation. The results showed that the content of emulsifiers had great effect on the stability of polymerization and then the morphology of the as-prepared microspheres. At a given content of SDS, MPS content had a great impact on the morphologies of hybrid microspheres. The hybrid particles had a "bowl-type" structure without MPS. With more and more MPS in the formulation, hybrid microspheres changed into a collapsed hollow structure. Silica nanoparticles with size of about 20 nm were on the outer shells of polymer microspheres.(6) A facile method for the preparation of silver/polystyrene (Ag/PS) composite microspheres was discovered. PS microspheres with carboxyl and nitrile groups on the surfaces were synthesized via a two-step dispersion copolymerization of styrene, itaconic acid, and acrylonitrile in ethanol/water media. Ag/PS composite microspheres were prepared successively by the addition of AgNO3 aqueous solution to the dispersion since Ag+ions were absorbed on the modified surfaces of PS microspheres, and then reduced to silver nanoparticles by aqueous hydrazine hydrate. The results showed that Ag nanoparticles with size of about 50 nm located on the shell of PS microspheres due to the interaction between the carboxyl and nitrile groups of PS microspheres and the in situ formed silver nanoparticles. The as-prepared Ag/PS microspheres showed good catalytic properties.(7) A rapid and facile method of preparing free-standing colloidal crystals from monodisperse charged polystyrene (PS) microspheres was proposed. Mixed solvents (ethanol/water) were used as the dispersion medium in the self-assembly process of colloidal crystals. By a simple "floating self-assembly" method, PS microspheres floated on the surface of liquid and self-assembled into large area of three-dimensional (3D) ordered colloidal crystals within 15 min. Then epichlorohydrin was added in as a cross-linking agent to strengthen the colloidal-crystal film. The obtained colloidal-crystal film was free-standing and could be easily transferred to other substrates. Using tetrabutyl titanate as a titania precursor,3D porous TiO2 materials with rodlike skeletal structure were fabricated from the prepared free-standing colloidal crystal.更多还原