两亲嵌段共聚物分子有序聚集体的结构特性及其应用

【作者】 王英；

【导师】 郭荣；

【作者基本信息】 扬州大学 ， 物理化学， 2003， 硕士

【摘要】 应用无外加探针循环伏安法研究了两亲嵌段共聚物Pluronic F127（F127）在铂电极上的循环伏安行为，探讨了F127在铂电极上的电化学反应机理。在此基础上测定了F127在水溶液中不同形态聚集体的扩散系数，得到第一CMC（临界胶束浓度）为3.72×10⁴ mol·L^-1，球形胶束向棒状胶束转变的第二CMC为1.49×10^-3mol·L^-1。这与以稳态荧光光谱法(3.98×10^-4 mol·L^-1和1.42×10^-3 mol·L^-1)和外加探针循环伏安法(4.31×10^-4 mol·L^-1和1.36×10^-3 mol·L^-1)测得的F127的第一和第二CMC值非常一致。随F127溶液浓度的增加，其临界胶束温度（CMT）逐渐降低，并且1/CMT与lnX_CMC呈线性关系，从而得到两亲嵌段共聚物F127的胶束化焓ΔH⁰为314 kJ·mol^-1，胶束化熵ΔS⁰为1.14 kJ·mol^-1，胶束化自由能ΔG⁰为-25.89 kJ·mol（-1）。热力学分析表明，F127在水中的胶束化是熵驱动的热力学自发过程。 测定了两亲嵌段共聚物F127/n-C_nH_2n+1OH/H₂O体系的三元相图，结果表明：随着直链脂肪醇链长的增加，O/W和W/O微乳液区域以及立方状和六方状溶致液晶区域逐渐缩小，而层状液晶区域逐渐增大。在O/W区域，直链脂肪醇从水相转移到F127胶束相的增溶吉布斯自由能μ_t随链长增加而减小，表明链长较长的直链醇较易增溶到胶束相。正丁醇的加入有利于F127单体分子聚集形成胶束，使得F127溶液的CMT降低。随正丁醇含量的增加，球形胶束增长，扩散系数下降较快，正丁醇在球形胶束中增溶达饱和后，扩散系数下降趋势变缓，这可从F127溶液的粘度随正丁醇含量的变化关系得到证明。随温度升高，F127分子与胶束的扩散系数以及正丁醇在球形胶束中的最大增溶量均降低。 以两亲嵌段共聚物F127/n-C₆H₁₃OH/H₂O(aq Cd²⁺)体系形成的层状液晶和六方状液晶为模板制备CdS纳米微粒，所得粒子分布比较均匀，粒径分别在8～12nm和6～8nm之间。以生物指示剂亚甲基蓝为表面修饰剂制得CdS纳米修饰微粒。红外光谱表明亚甲基蓝与CdS纳米微粒在其表面通过化学键相互作用，促进了扬州大学硕士学位论文CdS纳米微粒的团聚。在CdS荧光发射光谱中，随亚甲基蓝浓度增加，荧光强度明显增强，但过量亚甲基蓝的加入，却对CdS纳米微粒的荧光起碎灭作用。亚甲基蓝与CdS纳米微粒所形成络合物的光解作用证明了荧光碎灭的电荷转移机制。更多还原

【Abstract】 The cyclic voltammetric behaviors of an amphiphilic block copolymer Pluronic F127 （F127） at a platinum electrode in aqueous solutions were investigated by cyclicvoltammetry. The mechanism of the electrochemical reaction of F127 at a platinum electrode was deduced. The diffusion coefficients of different-shape aggregates formed by F127 were determined on this basis. The first and the second critical micelle concentration （CMC）, corresponding to the formation of the spherical micelles and the the transition of the spherical to rod-like micelles, are 3.72 x 10^-4 mol#L^-1 and 1.49 x 10^-3 mol#L^-1 respectively, which are in good agreement with the results from the steady fluorescent method （3.98 x 10-4 mol#L-1 and 1.42 x 10-3 mol#L-1） and the cyclic voltammetry with probe （4.31 x 10-4 mol#L-1 and 1.36 x 10-3 mol#L-1）. The critical micelle temperature （CMT） decreases with the F127 concentration increasing, and the 1/CMT varies linearly with InXCMC, from which the thermodynamic parameters of theF127 micellization process were obtained. The standard enthalpy $H, entropy $Sand free energy $G of F127 micellization are 314 kJ#mol-1, 1.14 kJ#mol-1 and -25.89kJ#mol-1, respectively. The thermodynamic analysis shows that the micellization of F127 in aqueous solutions is an entropy-driven spontaneous process.The ternary phase diagrams of amphiphilic block copolymer F127 / n-CnH2n+1OH / H2O system were determined, in which the OAV and W/O microemulsion regions and the cubic and hexagonal liquid crystal regions shrink gradually, while the lamellar liquid crystal region enlarges with the length of the chain in the unbranched aliphatic alcohol increasing. In the O/W region, the Gibbs free energy @, for alcohol to transfer from the water continuous phase to F127 micellar phase increases with the chain length of alcohol, which indicates that it is easier for the alcohol with longer chain length to solubilize in the micellar phase. The added n-butanol facilitates the formation of F127micelles and makes the CMT of F127 solutions decrease. The diffusion coefficient of the F127 micelles decreases relatively fast at first with the increasing n-butanol content, and then the decreasing trend reduces after the solubilization amount of n-butanol in micelles reaches the maximum, which can be confirmed by the variation of the relative viscosity of F127 solutions. The diffusion coefficients of F127 monomers and micelles, together with the n-butanol content corresponding to the maximum amount of solubilization in micelles, all decrease with the temperature rising.The lamellar and hexagonal liquid crystals formed in the amphiphilic block copolymer F127 / n-C6H13OH / H2O （aq Cd2+） system were used as templates for preparing CdS nanoparticles. The diameters of the nanoparticles obtained are in the range of 8-12 nm and 6-8 nm, respectively, with a relatively narrow size distribution. The modified CdS nanopaticles were obtained with a bioindicator methylene blue （MB）. The FT-IR spectra indicate that the CdS nanoparticles interact with MB on its surface by chemical bond, which causes the aggregation of CdS nanoparticals. The fluorescence intensities of CdS nanoparticles enhance remarkably with the increase of MB concentration, but decrease with the excess of MB added, which can be explained by the charge-transfer quenching mechanism, according to the photolysis of the complex of CdS nanoparticals with MB.更多还原