Dissipative Particle Dynamics Simulations Of The Self-Assembly Of Amphiphilic Block Copolymers

Amphiphilic block copolymers in selective solution self-assemble into a variety of morphologies. Compared to small molecular weight amphiphiles, aggregates from amphiphilic block copolymers are more thermodynamically and kinetically stable. Aggregates of block copolymers in selective solution thus have the potential to be used in a broad range of applications, especially in the fields of drug delivery, microelectronics, and advanced materials. In the past decade, the self-assembly behaviors and aggregate structures of amphiphilic block copolymers have attracted considerable attention in experimental studies. The self-assembled microstructures of amphiphilic triblock copolymers are studied using a dissipative particle dynamics (DPD) approach.First, the self-assembled microstructures of amphiphilic block copolymers depend on the selectivity of solvents for each block. By changing the selectivity of solvents, defined in terms of the repulsive interactions between the solvent and the hydrophilic/hydrophobic particles, an extensive simulation study on the spontaneous formation of complex micelles from amphiphilic triblock copolymers in a dilute solution is presented. The dynamic pathways in the formation of these assemblies have been investigated using a particle-based dissipative particle dynamics approach. In addition, the potential mechanism behind the formation of these microstructures has also been studied, which may be helpful in explaining how these aggregates are formed and in understanding the general principle of amphiphilic molecules.There are extremely valuable to study the transformations of different morphologies assembled by amphiphilic block copolymers. We try to examine the transformations of different morphologies and the dynamic pathways in the formation of these assemblies. It is confirmed that in the same selectivity of solvents, initial microstructures are key factors on morphologies assembled by amphiphilic block copolymers. The potential mechanism behind the formation of these microstructures may be helpful for us to explain how these aggregates are formed.Next, we report an extensive simulation study on the spontaneous formation of complex micelles from coil-rod-coil amphiphilic triblock copolymers in dilute solution resulting from solvent selectivity. The amphiphilic molecule is built from one hydrophilic block on each side and a hydrophobic block in the middle. The rigidity of the rod block is introduced by adding a bond-bending potential of the angle among three subsequent particles in the hydrophobic block. The incorporation of rigid-rod block into the amphiphilic block copolymer results in the self-assembled microstructures and their corresponding properties that differ from those built from fully flexible amphiphilic molecules with the same conditions. By changing the selectivity of solvents, defined in terms of the repulsive interactions between the solvent and the hydrophilic/hydrophobic particles, we find that the aggregation morphology changes from bundle-like micelles to spherical and cylindrical micelles to elongated micelles and then to ring-like toroidal micelles, revealing that the selectivity of solvents is a key factor that determines aggregation morphology. In addition, we observe that the formation of toroidal micelles from coil-rod-coil amphiphilic triblock copolymers proceeds via the growth pathway, which is quite distinct from the conventional toroidal micelle coalescence pathway observed in the self-assembling process of fully flexible amphiphilic triblock copolymer systems. Chain packing in toroidal micelles formed from amphiphilic triblock copolymers with fully flexible hydrophobic and rigid-rod hydrophobic blocks is likewise investigated. The simulation results show that the rigid-rod middle blocks adopt only extended conformations while flexible-coil middle blocks can adopt both folded and extended conformations in toroidal micelles.In addition, we report the influences of the rigidity of hydrophobic blocks on the spontaneous formation of complex micelles from amphiphilic triblock copolymers in dilute solution. We confirmed that it is decided by the interactive energy between hydrophobic blocks and solvents and bond-bending energy in the spontaneous formation of complex micelles from coil-rod-coil amphiphilic triblock copolymers in dilute solution resulting from solvent selectivity. Meanwhile, we observe two different pathways in the formation of toroidal micelle assembled from coil-rod-coil amphiphilic triblock copolymers. These findings demonstrate that the bond-bending potential in amphiphilic molecules is an effective and relatively simple method to model the behavior of coil-rod-coil amphiphilic block copolymers.