Self-assembly Of SBS In Decane Solutin Studied By Spectroscopy

In the past years, the self-assembly of block copolymer in a dilute solution has attracted much scientific interest because of the potential applications of block copolymer in nanoreactors, nanomaterial, drug delivery systems, polymeric scaffolds for tissue engineering and so on. Physical gels formed from block copolymer in selective solvent have received widespread attention too, especially triblock copolymers with soluble middle block, due in part to their ability to range from viscous liquids to elastic solids on some conditions, thereby enabling a host of applications in the fields of coatings, cosmetics, and pharmaceutics. However, for the different concentrations of polymer solution formed from a triblock polymer dissolved in middle selective solvent, what transitions have gone through from the micellization in dilute solution to the gelation in concentrated solution? And how did the molecules self-assembled into different aggregations with the changing of concentration?In this dissertation, intrinsic fluorescence and light scattering methods were used to study the questions. The conclusion have been summarized as below:Temperature-dependent micellization behavior of SBS dissolved in n-Decane selective for the middle PS block was investigated by light scattering and fluorescence spectra. Light scattering results indicate that SBS block copolymers in the dilute solution (C= 2×10-5g/ml) can self-assemble into a rich variety of aggregates related with the change of temperatures, and its size is polydispersed with considerable effective diameter. The self-assembly was reversible during temperature cycle from 85℃to 10℃, and can be divided into three stages. A twisted conformation emission at 300nm was detected by intrinsic fluorescence in the poor solvent, and it was different from the monomer and excimer emission in solutions of polystyrene. Associating with atomic force microscope techniques (AFM), it was concluded that SBS tri-block copolymer in each stage can aggregate into different morphology, including primary micelles (Ⅰ), micelle aggregations (Ⅱ), and partial network formed by micelles (Ⅲ).The gelation of SBS/Decane solution depending on temperature was confirmed having three stages through elasticity light scattering and dynamic light scattering. (Ⅰ) Formation of gel networks,80℃> T> 44℃; (Ⅱ) Shrinkage of micelles core composed the networks, 44℃> T> 26℃; (Ⅲ) Subprime aggregations,26℃> T> 10℃. Three peaks are obvious in the fluorescence spectrum of gelation process. Two-dimensional correlated spectroscopy has been used to validate the third peak at 300nm, and differentiate the sequencing of the three peaks changed at different temperature range.The configuration of SBS/Decane solution at room temperature with different concentrations is quite different. The elasticity light scattering at the solutions of 2×10-4g/ml, 2×10-3g/ml and 2×10-2g/ml are similar: there exists one peak on their own light scattering curves, because phase separation and anomalous scattering occurs. But the temperature peak of the polymer concentration of 2×10-2 g/ml was shifted to low temperature, due to the formation of gel networks and the plentiful intermolecular association concomitant. Howerve, the results of fluorescence spectra are different. The temperature-dependent curves of maximum fluorescence peak and the excimer/monomer fluorescence ratio (Ie/Im) of SBS/decane solution are similar when the concentration are 2×10-4g/ml and to 2×10-5g/ml, and the curves are similar when the concentration are 2×10-2g/ml and to 2×10-3g/ml. Light scattering is much more sensitive then fluorescence spectra at the detecting of phase separation of polymer solution. Besides, The existence of insoluble PS segment was confirmed by fluorescence spectra in the polymer solution (C= 2×10-2g/ml) at the measurable temperature range.