Self-assembly Of Amphiphilic Triblock Copolymer In Selective Solvent And Its NMR Study

Block copolymer can self-assemble into "core-shell" micelles in selective solvent. Ithas become an important topic in polymer and materials science to form the nanomaterialsbased on the templates of block copolymer self-assembles because these assembles are innanometer scale. Great effort have been given to the formation of various micellarmorphologies from the self-assembly of amphiphilic triblock copolymer in selective solvent. In this study, Monte Carlo simulation and experimental methods were combined to studythe self-assembly of amphiphilic triblock copolymers in selective solvent. It was focused onthe effects of the selective solvent addition on the self-assembly of block copolymer. Thefollowing results were abtained: 1. Micellar morphologies, such as sphere, rods, and the coexistence of spheres and rodswere obtained from Monte Carlo simulation. The aggregate morphology transition fromspheres to rods would occur by increasing the interaction between the middle block andwater. 2. In our simulation, the amphiphilic triblock copolymer were firstly dissolved into acommon solvent; then the selective solvent for the middle block of the copolymer (i.e.,water) was added gradually into the solution to induce the self-assembly of the copolymer.Core-shell micelles would be formed when the water content reached a critical value. Mostof the water would aggregate around the chains of the copolymer at first with the wateraddition, then more and more water is likely to diffuse into the solution by wateraddition .The interaction between the copolymer chains and water is one of the main reasonsfor the micellization. Water concentration in the solution plays a key role during theprocesses of the micellization. 3. NMR was used to study the interaction between water and the triblock copolymer(P4VP-b-PS-b-P4VP) during the self-assembly processes. Hydrogen bonding existedbetween the hydrophilic segments and water in the solution. NMR results indicate that mostwater aggregated around the hydrophilic segments of the copolymers at first with wateraddition, then most water diffused in the solution after the water content reached a criticalvalue. It was found that the interaction between the copolymer and water occurred alreadybefore the appearance of the micellization. Water concentration plays an important role inthe processes of the micellization. The results correlate well with simulation. The results give an insight in to the self-assembly behavior of block copolymer inselective solvent and show us how to control micellar morphologies.