Molecular dynamics study of the solution of semiflexible telechelic polymer chains with strongly associating end-groups

Abstract

We present the results of molecular dynamics simulations of micelle organization as well as the formation of micellar aggregates in the solutions of semiflexible telechelic chains with strongly attracting end-groups (“sticker sites”). Using the cluster size distribution function, we study associative equilibrium in the system of flexible and semiflexible chains. It is found that this process corresponds to the so-called “open association” model for micelle formation. The critical temperature of micelle formation Tc is calculated as a function of chain rigidity and system density ρ. We find that the value of Tc increases monotonically with the increase of Kuhn segment length A. Such a behavior takes place in wide range of densities, but only if the value of ρ is somewhat smaller than some threshold value. At high density, we observe the opposite tendency; the temperature Tc decreases monotonically as the value of A is increased. The type of equilibrium microstructures, emerging as a result of micellization in the strong segregation regime, depends essentially on the chain rigidity. In the case of flexible telechelic chains, relatively small flowerlike micellar aggregates are observed. For the system of semiflexible chains, we find rather distinctly appearance of microbundles with pronounced liquid-crystalline-like order. In this case, the spatial organization of the system is characterized by a cellular architecture which looks like “ceramics.” Thus, significant morphological changes can be induced by varying of chain rigidity. At fixed system density and T<Tc, the characteristic period rm of locally ordered micellar arrays scales as rm∝Ã1/3, where à is the reduced statistical segment length. Also, it is shown that the average aggregation number increases as the chain rigidity is increased. In other words, the gradual stretching out of the chains shifts the association equilibrium to formation of larger clusters. We have performed a comparative analysis of our computer simulation data with theoretical predictions. It is shown that the simple theoretical model is successful enough to explain some basic features observed in simulations.