可聚合凝胶因子的聚集组装、凝胶化及其分形模型

Many solvents can be gelated by some of low molecular weight compounds at low concentrations (typically < 1wt%) and form thermally-reversible viscoelastic liquidlike or solidlike materials that are called molecular gels or organogels. Such low molecular weight compounds are called "gelator". Most of organogels from gelators in solvents is unstable and easily transform from the metastable gels to a crystalline state. By design of gelator, a new polymerizable gelator with a bis(ethylene) groups, 4,4'-bis(α-methylacryloyloxy-1,3- ethyleneoxycarbonylpropionamido) diphenyl methane (BMDM), has been synthesized and tested for their ability to cause gelation of organic solvents. The thermoreversible physical organogels can be formed by BMDM in many aromatic solvents, for example, benzene , toluene, xylene and diphenyl ether. But BMDM is dissolved in strong polar solvents such as DMF, ethanol and dichloromethane, and precipitated in apolar solvents such as ether and petroleum ether. The present of intermolecular hydrogen-bonding in the organogels were proved by the FT-IR spectra. The measurements of differential scanning calorimetry (DSC) also indicated that the self-assembled aggregates of the organogels occured as a result of cooperating noncovalent interactions such as intermolecular hydrogen-bonding. .By in situ photopolymerization of the gelled solution, the scaffoldlike structure of the gels was locked and the gels form more stable well-ordered superstructure. The stable time of the polymerized gels is more than one year. However, the stable time the unpolymerized molecular gels is only from several days to several weeks. The studies of polarized optical microscopy and TEM indicate the formation of single axis negative spherulites undergoing aggregation of self-assembled fibers. And the color sequence from the spherulites in POM is the first-order sensitive tint. It were found by DSC that the potential barrier (Peak 1) for disassociation of spherulites formed by van der Waals interaction was DH = 0.8 kJ×mol-1 and the enthalpy (Peak 2) of gel-sol phase transition for fibers aggregated by hydrogen bonding was DH = 22.3 kJ×mol-1. For polymerized gels there is only a volume phase transition, without a gel-sol phase transition. The temperature of volume phase transition for polymerized gels is about 110～120 ℃ higher than that of the unirradiated gels. Swelling behavior of the dried polymerized gels follows Schott second-order diffusion kinetics. The degree of cross-linking is a main fact influencing the swelling behavior of the gels. Organogel orientation has been studied by means of polarized fluorescence. It was found during the process of the sol-gel phase transition that the isotropic solution (P0 = 0) with BMDM was translated to an anisotropic sol (P > 0), and lastly the anisotropic sol became the isotropic gels (Pgel ≈ 0). X-ray powder diffraction and atom force microscopy revealed that the fibril bundles consist of well-ordered stacks of ribbons or sheets. The width of a ribbon is 3 nm, and its thickness is 0.1~0.2 nm. It was also shown that the aggregates of gels have a well-ordered lamellar structure, self-comparability and typical fractal characteristic. With the help of fractal theory and C++ program, fractal dimension D of the fractal structure can be calculated to be D = 1.8~1.9 through Sandbox and density-density correlation function methods. The difference of the two methods, and the formation mechanism of the fractal structure are also discussed.

凝胶因子能在较低浓度下在大多数有机溶剂中因分子间相互作用聚集、组装有序高级结构，使溶剂凝胶化。但其稳定性欠佳。合成可凝合凝胶因子先聚集使凝胶化，后聚合形成凝胶网络。探讨聚集作用本质并以凝胶因子作为分形的生成元，应用分形理论揭示各层次聚集体与组装单元间的关系。本项目在提高聚集体结构稳定性并用分形理论建立聚集模型有意义。