Amphiphilic Block Copolymer Molecules Ordered Aggregate Structure Properties And Applications

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.