The Structural Regulation And Morphological Transition Of Tri-block Copolymer Micelles

Block copolymer can self-assemble into various micellar morphologies in selective solvent,which have potential applications in the field of biomedical and photoelectric material.Compared with the diblock copolymer,ABC triblock copolymer can form more complex muliticompartment micelle structure.It shows more controllability and diverse than amphiphilic block copolymer nanoscale.In this dissertation,a series of ABC triblock copolymer micelles were investigated through the different preparation methods under control of thermodynamic and kinetic conditions,moreover,the factors which may affect the micellar morphology and morphological transition in solution were discussed.ABC triblock copolymer micelles were prepared by selective solvent addition method.The morphological transition of micelles were explored by changing different factors,such as triblock terpolymer concentration,the block chain ratio and the addition rate of selective solvent.It was found that cylindrical micelles transform into spherical micelles abnormally with increasing block copolymer concentration,the solvophobic block and the addition rate of selective solvent.Nanotubular micelles with high aspect ratio were prepared through thermal annealing method,where the nanotubular formation mechanism is explained and compared with the conventional pathway.When thermal annealed at a high temperature above the critical transition temperature and below the critical micellization temperature,the block copolymer micelles went through a unique relaxation-reaggregation process.Depending on the thermal annealing time,aggregation degree reaggregated in the cooling process into various 1D metastable micellar structures at the same thermodynamic conditions.The influence of thermodynamic parameters on the kinetic pathway of morphological transition was investigated.It was found that the critical transition temperature(CTT)and critical micellization temperature(CMT)depended on the triblock terpolymer concentration solvent composition and the block ratios.The CTT of system moved to high temperature to reduce the rate of morphological transition with an increase in triblock terpolymer concentration and content of selective solvent.As stated above,the influences of the micellization and morphology trasition kinetic pathway on the block copolymer self-assembled structures were discussed,and the possibility to tune the kinetic pathway through thermodynamic conditions was also demonstrated.These results not only bring in new ways to prepare well-defined 1D self-assembled micellar structures,but also provide a deeper insight into the intrinsic physics of block copolymer self-assembly.Moreover,it is expected to offer a guideline for the potential application of 1D nanostructure in areas such as controlled release and hybrid nanomaterials.