We studied the self-assembly dynamics of two polymeric systems, block copolymer micelles and supramolecular polymer solutions using computer simulation.
Dissipative Particle Dynamics simulations were applied to study the equilibrium properties, kinetics of micellization and equilibrium chain-exchange in A2B3 and A4Bx(x=4,6,8) diblock copolymer micelle solutions. The critical micelle concentration, micelle aggregation number distribution and micelle structure were found to agree well with previous experimental and theoretical studies. The time-evolution of micelles from unimers is found to follow three stages: unimer consumption, equilibration of the number of micelles progressing mainly by the fusion/fission mechanism and slow adjustment of the weight-average aggregation number by micelle fusion, unimer and small aggregate exchange. The effect of polymer concentration, hydrophobic interaction energy and block length on the kinetics of micellization were also considered. By performing micelle hybridization simulations, we found the equilibrium chain exchange follows a first-order kinetic process and the characteristic time, mainly determined by chain expulsion and does not depend on polymer concentration. The chain exchange characteristic time, τ, increases exponentially with core block length, NA and interaction parameter between blocks, χAB as τ ~ exp(0.67χABNA). We also found that in contrast to theoretical predictions, chain exchange between micelles occurs more rapidly for micelles with a longer corona-block length due to a higher compatibility of diblock copolymers and therefore a lower potential barrier for chain expulsion.
Using coarse-grained molecular dynamics simulations we studied the equilibrium and rheological properties of dilute and semi-dilute solutions of head-to-tail associating supramolecular polymers with our newly-developed model for spontaneous reversible association. We found that for a given spacer length all shear-rate-dependent reduced viscosity data collapse into one master curve with two power-law regions with increasing
slopes due to change of the degree of self-assembling under shear. The equilibrium viscosity is found to obey a power-law scaling dependence with exponent 1.5 on oligomer volume fraction, in agreement with experimental observations for several dilute or semi-dilute solutions of supramolecular polymers, implying that dilute and semi-dilute supramolecular polymer solutions exhibit high polydispersity, but may not be sufficiently
entangled to follow the reptation mechanism of relaxation, expected for wormlike micelles.