【作者】 段铃丽；

【导师】 武利民；

【作者基本信息】 复旦大学 ， 材料物理与化学， 2010， 博士

【摘要】 单分散的、亚微米级的胶体粒子在特定条件下组装,可形成胶体晶体或粒子胶囊。胶体晶体在电子带隙材料,传感器、颜料和模板材料上有广泛应用。目前,用于自组装胶体粒子主要为二氧化硅、PS、PMMA等硬粒子。由硬粒子自组装的胶体晶体膜易开裂,强度低,限制其大规模使用。成膜性聚合物乳胶粒子可赋予胶体晶体膜很好的力学性能,但由于其缺少折光指数的差异而无法显示晶体膜的结构色,因此很少被用作胶体晶体的组装材料。本文以含亲水性壳层的聚合物乳胶粒子为组装单元获得了溶剂响应性胶体晶体膜；以聚合物乳胶粒子和二氧化硅纳米粒子进行二元共组装制备了可逆应力响应性胶体晶体膜。粒子胶囊广泛用于物质的包覆,而响应性粒子胶囊的尺寸能随外界环境的改变而变化,因此它则能为被包覆物质的释放提供更多的控制途径,但目前响应性粒子胶囊的研究进展有限,基于此情况,我们制备了温敏性粒子胶囊。具体研究内容和结果如下：(1)以乳液聚合合成含亲水性壳层的聚合物乳胶粒子,并以此为组装单元,获得具有可逆溶剂响应性和力学性能的聚合物晶体膜及其大面积制备方法。胶体晶体膜由涂覆在基材上的乳液在室温下干燥直接制备。干燥过程中乳胶粒子自组装成有序结构,从宏观上可由乳液边缘出现的绚丽色彩显示出来。干燥过程中,乳液边缘的反射峰位不断向短波长方向移动,峰强逐渐减弱,直至完全消失。最终可得到无色透明聚合物胶体晶体膜。通过SEM和AFM观测该膜形貌,结果表明乳胶粒子形成规整的fcc结构,膜的表面为fcc的(111)晶面,并且无论乳胶粒子是否含亲水壳层都不影响粒子的规整组装。该无色透明聚合物胶体晶体膜被水润湿后,可以显示对应的结构色彩。当水分挥发完全,该晶体膜又重回无色透明状态,具有可逆的溶剂色彩响应性。这种水响应色彩现象的原因是水和与亲水性壳层作用时,亲水性壳层的折光指数变化,因此体系有足够的折光指数的差异,从而显示对应的结构色彩。湿膜的结构色彩和乳胶粒子的大小、亲水壳层的厚度和干燥温度有关。其它能和亲水链段作用的有机溶剂如甲酰胺、乙醇等也能使该胶体晶体膜显示出对应的结构色彩。(2)以聚合物乳液和二氧化硅纳米粒子共混,室温干燥成膜,聚合物乳胶粒子和二氧化硅纳米粒子发生共组装,获得了具有可逆力学响应性的聚合物晶体膜及其大面积制备方法。SEM和同步辐射USAXS研究表明,二氧化硅粒子在胶体晶体膜中起到了阻止聚合物粒子完全融并的作用,但同时乳胶粒子并没有被二氧化硅纳米粒子完全分隔开,相邻的乳胶球之间仍有相连接的部分,使得制备的胶体晶体膜具有力学强度。通过调整软硬单体的比例和交联剂的用量可以得到不同力学强度和回复性的胶体晶体膜。原位反射光谱记录了拉伸及回复过程中该膜的结构色彩变化：拉伸过程中,聚合物晶体膜的颜色随着应变的增大而逐渐蓝移,其反射峰位的变化可达到230 nm。拉伸时反射峰位和应变成线性关系。外力撤去后,该膜反射峰位开始逐渐红移,最终回复到和初始峰位基本一致的位置。(3)以纳米SiO2作Pickering乳化剂,采用反相悬浮聚合得到了温敏性的PNIPAm/SiO2复合粒子胶囊。先合成不同粒径的单分散纳米Si02粒子,并使用硅烷偶联剂MPS或DCMS改性,经改性过的两亲性纳米SiO2粒子在W／O液滴的界面上组装。并向水相中引入温敏性单体NIPAm,通过Pickering反相悬浮聚合得到了复合的二氧化硅的粒子胶囊。聚合过程中,以MPS改性的大粒径(500nm,962 nm)的纳米SiO2粒子为Pickering乳化剂时,聚合过程不稳定,反应时出现絮凝。而纳米SiO2用量少于0.64 wt%时,聚合过程也不稳定。粒子胶囊的尺寸和二氧化硅粒子的粒径有关,二氧化硅粒径越大,粒子胶囊尺寸越大。SEM结果显示二氧化硅粒子在凝胶球表面规整排列,当水凝胶的交联度过大(交联剂用量达0.32%),大粒径的二氧化硅粒子容易从塌缩的凝胶球表面脱落。降低交联剂用量可避免该现象。该复合的粒子胶囊具有温敏性。胶囊表面的SiO2粒子对PNIPAm的相行为没有影响,升温至32℃时复合粒子胶囊开始收缩,以MPS改性的SiO2制备的粒子胶囊在升温过程中收缩率低于以DCMS改性制备的粒子胶囊。通过测定被包覆的亚甲基蓝染料的释放测试表明,二氧化硅粒子的粒径越大,温度越高,被包覆的染料释放越快。而染料在MPS改性的二氧化硅制备的粒子胶囊中的释放速率低于在DCMS改性二氧化硅制备的粒子胶囊中的释放速率。更多还原

【Abstract】 Colloidal crystals and colloidosomes can be accomplished by bottom-up methods based on self-assembly of monodisperse colloidal particles. Colloidal crystals have some important potential applications, such as photonic crystals, sensors, templates, and even paints. The building blocks of colloidal particles are generally "hard" beads, typically silica, polystyrene or poly(methyl methacrylate) spheres. As a result, the obtained crystal film has little mechanical strength. By now, film-forming polymer latex spheres are seldom used as building blocks in colloidal crystal films, since they are likely to deform and merge into a continuous matrix. However, films based on film-forming polymer latex are widely used for their flexibility, robustness and thermomechanical properties. The combination of optical property of colloidal crystal and flexibility of soft latex film can greatly expand the application of colloidal crystal film. Here, monodisperse polymer latexes containing hydrophilic shell were used to prepared solvatochromic-responsive crystal film. When polymer latex co-assemble with the silica nanoparticles, mechanochromic-responsive crystal films can be directly obtained. Colloidosomes can be used in encapsulation and controlled release. However, the driving forces for release of the encapsulated materials are only from osmotic pressure and rupture of outer shell. The limitations highlight the need for fabrication of colloidosomes with new properties, which can response to the changes of environmental stimuli. Therefore, temperature-responsive composite colloidosomes were prepared in this dissertation. The detail contents and results are summarized as follows:(1) A reversible solvatochromic-responsive crystal film based on the film-formation of "soft" monodisperse polymer latex. In this approach, a monodisperse polymer latex containing hydrophilic monomers was first synthesized using one-pot emulsion polymerization method and then cast on substrates, followed by dried at certain temperatures, a colorless and transparent crystal film was directly obtained. When this film meets water or some other polar solvents, brilliant colors appear; when this wetted film is completely dried again, the colors disappear and the film revert to the original colorless and transparent state. This reversible solvatochromic-responsive behavior is attributed to both the periodic structure of polymer film and the contrast of refractive index between core and shell due to the interaction between solvents and hydrophilic shell. However, if the film was obtained by too high drying temperature, e. g.,100℃, or too low content of hydrophilic monomers, e. g.,0.5% or less, no color appeared.(2) A reversible mechanochromic-responsive crystal film based on the room-temperature film-formation of monodisperse polymer latex by the aid of nanosilica particles. In this approach, when the "soft" colloidal polymer spheres were blended with colloidal silica particles and then cast on a substrate, followed by drying at room temperature for self-assembly, an elastic crystal film was directly obtained. These "soft" polymer spheres can self-assemble into three-dimensional ordered crystal film since nanosilica particles can effectively obstruct the coalescence and highly deformation of these "soft" polymer spheres during film formation. This crystal film has not only reversible and repeatable mechanochromic-responsive property, but also tunable color and peak position covering almost entire visible spectral region, depending upon the sizes of polymer spheres and strains. This optical response is attributed to the variation of lattice spacing during deformation.(3) Thermal-responsive poly (N-isopropylacrylamide)/silica composite colloidosomes were synthesized via inverse Pickering suspension polymerization using various sizes of silica particles as stabilizers. The droplets of N-isopropylacrylamide aqueous solution were first emulsified in toluene and stabilized by modified silica particles, and then polymerized to obtain PNIPAm/silica composite colloidosomes. Preliminary studies showed that these PNIPAm/silica composite colloidsomes had similar thermal-responsive behavior as pure microgel with the LCST of 32℃. The colloidosomes prepared by MPS modified silica and DCMS modified silica showed different thermal-responsive behavior and dye release rate. The release experiments showed that release rate of the microspheres increased with increasing silica size and the temperature, indicating that the releasing property can be either controlled by the particle size of silica or the temperature.更多还原