基于聚合物及阴离子表面活性剂的材料组装合成

【作者】 李丽颖；

【导师】 陈铁红；

【作者基本信息】 南开大学 ， 物理化学， 2008， 博士

【摘要】 通过模拟自然界中生物矿物的形成过程、借鉴生物矿化的机理,制备复杂形貌和多级结构高级材料的仿生合成或生物启发合成方法,是近些年来一直备受关注的前沿课题。碳酸钙、羟基磷灰石和二氧化硅是生物矿物中最常见的成分,研究它们的仿生合成,对理解生物矿化的机理具有重要的指导意义,进而,对生物矿化机理的探索,又可以为仿生制备新型功能材料提供理论指导和设计依据。有机质(聚合物、表面活性剂或小分子)与无机组分之间的相互作用是控制材料组装和结构的核心,本论文通过设计聚合物和氨基酸阴离子表面活性剂与二氧化硅前驱体或钙离子之间的作用,组装合成二氧化硅、碳酸钙、磷酸钙材料。主要内容有以下几部分:1.设计合成富含侧链羧基的阴离子多肽聚L-谷氨酸,并以其作为模板剂,以3-氨丙基三甲氧基硅烷(APMS)和正硅酸乙酯(TEOS)为硅源,控制合成了微孔二氧化硅空心球。在合成过程中,硅源与阴离子多肽模板之间的组装依照以阴离子表面活性剂为模板剂组装合成介孔二氧化硅的机理,即S-N+~I-机理,其中S表示阴离子多肽, I表示TEOS,N表示共结构导向剂APMS。组装过程中质子化的APMS与阴离子多肽之间形成静电相互作用,同时,APMS和TEOS共同水解聚合形成围绕阴离子多肽模板的二氧化硅骨架,多肽的二级结构为微孔孔道的模板。运用SEM、TEM、N2吸附详细考察了二氧化硅的形貌和结构。以阴离子多肽为模板,通过控制不同的反应条件,可以分别合成直径约170 nm的微孔空心球(比表面积为161m2/g),直径约为380 nm的微孔实心球(比表面积为400m2/g)和直径约为550 nm的微孔空心球(比表面积为350m2/g)。向多肽的水溶液中加入适量的有机溶剂四氢呋喃,得到直径约为200 nm的介孔二氧化硅实心球(比表面积为304 m2/g)。2.以阴离子聚合物聚丙烯酸(PAA)为模板,以3-氨丙基三甲氧基硅烷(APMS)和正硅酸乙酯(TEOS)为硅源,按照S-N+~I-机理合成了聚丙烯酸-二氧化硅(PAA/SiO2)复合纳米球。SEM、TEM、TG、FT-IR表征证明,合成的纳米球是聚丙烯酸和二氧化硅复合物,直径约为80 nm。复合纳米球焙烧后的N2吸附-脱附等温线表明,以柔性链的PAA分子作为模板合成的二氧化硅粒子不具有孔结构,对比相同实验条件下利用聚谷氨酸钠作为模板得到微孔二氧化硅的结果,进一步说明聚谷氨酸钠的刚性二级结构是制造微孔结构的模板。此外,在合成PAA/SiO2复合纳米球的体系中,加入不同量的有机溶剂THF能够对复合球的形貌产生影响。在合成PAA/SiO2复合纳米球的体系中,通过引入阴离子表面活性剂Sar-Na控制合成了超微孔结构二氧化硅,BET表面积761 m2/g,孔体积0.57 cm3/g,通过MP方法计算得到孔径为1.2 nm。3.设计合成双亲性嵌段共聚物聚乙二醇-聚L-苯丙氨酸,利用固体NMR技术研究其相分离结构、构像、结晶性及微区分子运动。通过1H CRAMPS和13C CPMAS TOSS固体高分辨NMR实验发现随多肽链长的减小,嵌段共聚物中的多肽链的α-螺旋构象逐渐减少,无定形的多肽结构增加,同时PEG的结晶度逐渐增加。采用1H偶极滤波自旋扩散NMR实验测定了不同多肽链长下的嵌段共聚物中的PEG非晶区的相区尺寸。发现随着肽链长的减小,PEG由于结晶度的提高使非晶区的相区尺寸明显减小。综合采用偶极滤波、双量子滤波、2D WISE和2D LG-CP多种固体NMR实验技术详细研究了嵌段共聚物中的多肽链及PEG链段的分子运动特性。发现在嵌段共聚物中的多肽链段由于有α螺旋构象的存在而非常刚性,但也有很少量靠近嵌段点附近的氨基酸受PEG影响而运动较快。非晶区PEG本身运动很快,但也发现少量的嵌段点附近的PEG受嵌段多肽的影响而变得较刚性。4.利用蒸发诱导自组装方法(Evaporation-Induced Self-Assembly,EISA),分别以聚氨基酸聚γ-谷氨酸苄酯(PBLG)和聚乙二醇-聚L-苯丙氨酸(PEG45-b-Phen)为模板,以硅烷偶联剂苯氨甲基三乙氧基硅烷(AMTS)和正硅酸乙酯(TEOS)为硅源,通过氨基酸侧链苯环与AMTS分子苯环之间的π-π堆积作用,合成了微孔二氧化硅材料。当嵌段共聚物PEG45-b-Phen中苯丙氨酸链段较长时(n=50),能够对二氧化硅的形貌起到很好的控制作用,得到了大小均一,分散性很好的梭形聚合物/二氧化硅复合材料,这种梭形的粒子的长约8μm、中间部位宽约1.6μm。5.利用工业中广泛应用的无毒、低成本、可生物降解的含有氨基酸结构的阴离子表面活性剂N-酰基十二烷基肌氨酸钠(Sar-Na)作为添加剂,分别在水、乙醇、乙醇-水二元体系中,在室温的条件下合成碳酸钙。在水体系中得到球霰石空心球;在乙醇体系中得到球形无定形碳酸钙;在乙醇-水二元体系中合成了花簇状多级结构碳酸钙晶体。在水热条件下,利用N-酰基十二烷基肌氨酸钠(Sar-Na)控制合成了具有较大长径比(aspect ratio)的片状纳米羟基磷灰石晶体(HAP)。调整体系的pH值能够对HAP晶体的形貌产生影响,随着pH值由9.1变化到10.0、11.0、12.0,HAP晶体的形貌由两端较尖锐的长片状变为短棒状,最终变为椭圆形粒子。在Sar-Na调控合成羟基磷灰石的体系中,加入阴离子聚合物PAA,HAP晶体的形貌发生变化,随着PAA添加量的增加,片状形貌逐渐消失,形成无规则形貌的晶体。更多还原

【Abstract】 Biominerialization is the study of the formation, structure and properties of inorganic solids deposited in biological systems. That is, under certain chemical conditions, the inorganic ions in solution are transformed to solid minerals under the specific control of the organic species. Biomimetic or bio-inspired materials chemistry is currently a promising field to synthesize functional inorganic materials. Calcium carbonate, hydroxyapatite and silica are the most common biominerals in nature, and bio-inspired synthesis of those materials would shed light on the study of mechanism of biomineralization, and be significant to the synthesis and design of new functional materials.The interaction between organic and inorganic species controls the growth of inorganic materials, as well as their structures and morphologis. In this thesis, by designing the interactions between the organic species (polymer and anionic surfactant) and the inorganic precursors, different types of silica, calcium carbonate and hydroxyapatite were synthesized. The main content is as follows:1. Anionic polypeptide, the poly(sodium L-glutamate), was applied to fabricate microporous silica hollow nanospheres templated by the secondary structures of the polypeptide as porogens. In the synthesis, 3-aminopropyltrimethoxysilane (APMS) and tetraethyl orthosilicate (TEOS) were used as the silica sources, and the coassembly follows the mechanism of the anionic surfactant–templated mesoporous silica (AMS) through a S?N+?I? pathway, where S indicates the anionic polypeptide, I indicates inorganic precursors (TEOS), and N indicates costructure-directing agent (APMS), which interacted with the negatively charged anionic polypeptide secondary structures electrostatically and cocondensed with silica source to form the silica framework. The product was subjected to characterizations of X-ray diffraction (XRD), infrared spectroscopy (IR), thermogravimetric (TG) analysis, scanning electron microscopy (SEM), transmitted electron microscopy (TEM), and nitrogen adsorption-desorption measurement. It was found that the pH value of the synthesis solution was an important factor to the morphological control of the silica products. Besides the microporous hollow nanospheres, microporous submicron silica solid and hollow spheres were also obtained facilely by changing the synthesis parameters. Our study further implies that anionic polypeptides, which are able to control mineralization of calcium carbonate and calcium phosphate, could also induce silica condensation in the presence of proper silica precursors. It is also expected that functional calcium carbonate (phosphate)/silica–nanocomposite materials would be fabricated under the control of the anionic polypeptide.2. The anionic polymer, poly(acrylic acid) (PAA), was used together with APMS and TEOS as silica source to synthesize composite nanospheres of PAA/silica. The results indicate that after calcination the silica nanospheres is non-porous, and this can be explained by the lack of the secondary structure of the PAA chains if compared with polypeptide chains. Furthermore, it has been proved that addition of organic solvent such as THF would influence the morphology of the products. By introduction of anionic surfactant in the reaction solution, super-microporous silica can be obtained with the BET surface area of 761 m2/g and pore size of 1.2 nm.3. Amphiphilic block copolymers, poly(L-phenylalanine)-b-poly(ethylene glycol), were synthesized and the properties of phase separation, conformation, crystalline property and micro domain motion were subjected to detailed solid state NMR studies. By the methods of 1H CRAMPS and 13C CPMAS TOSS NMR, it was found that with the decreasing of the polypeptide chain length, theα-helix conformation decreased, amorphous structure increased and the crystallinity of PEG chain increased. By 1H spin diffusion NMR the domain size of the amorphous PEG was determined and it was found that with the decreasing of the polypeptide chain length, the domain size of amorphous PEG decreased obviously. The molecular motion in the copolymer was characterized by dipolar filter, double quantum filter, 2D WISE and 2D LG-CP NMR methods. It was found that due to the existence ofα-helix the polypeptide chain is rather rigid, while the motion of the amorphous PEG is fast.4. Poly (γ-benzyl-glutamate)(PBLG) and amphiphilic block copolymers, poly(L-phenylalanine)-b-poly(ethylene glycol), were used to fabricate silica materials by Evaporation-Induced Self-Assembly (EISA) method. In the synthesis procedure, anilino-methyl triethoxy silane (AMTS) was used as an intermedium, i.e., on the one hand it interacts with polypeptide-based copolymer throughπ-πinteraction between the phenyl groups of Phe segments and AMTS; on the other hand, AMTS can co-condense with tetraethoxylsilane (TEOS) through hydrolysis process. The prepared silica possesses supermicropores and it is proposed that the supermicropores are templated by the polypeptide segments. It is proved that both polypeptide-based block copolymer and AMTS play important roles in the formation of mesoscale short-range-order and hierarchical structure. It is noted that PEG45-b-Phe50 can induce a well-defined shuttle-like morphology of polymer/silica hybrid particles.5.N-lauroylsarcosine sodium (Sar-Na) was used to control calcium carbonate crystalization in ethanol or ethanol/water solution at ambient temperature. By means of SEM, XRD and IR, the morphology and structure of the samples were characterized. It was revealed that with increasing the reaction time, the morphology of the CaCO3 particles generally varies from aragonite polyhedron to amorphous calcium carbonate spheres in pure ethanol. In the ethanol/water solution, with increasing the amount of N-lauroylsarcosine sodium, the morphology of the CaCO3 particles varies from flower-like to spheres. Pure vaterite crystals with spheres shape are obtained at n(Ca): n(Sar)=1:2. At a fixed n(Ca): n(Sar) molar ratio of 1:1, with increasing the volume fractions of distilled water, the morphology of the CaCO3 particles varies from flower-like to spheres. By hydrothermal reaction method under the control of N-lauroylsarcosine sodium, single crystal hydroxyapatite nano-plates was synthesized and the different synthesis conditions were carefully studied.更多还原