Diagram of states and morphologies of flexible-semiflexible copolymer chains: A Monte Carlo simulation

Abstract

A single copolymer chain consisting of multiple flexible (F) and semiflexible (S) blocks has been studied using a continuum bead-spring model by Stochastic Approximation Monte Carlo simulations, which determine the density of states of the model. The only difference between F and S blocks is the intramolecular bending potential, all non-bonded interactions are equal. The state diagrams for this class of models display multiple nematic phases in the collapsed state, characterized through a demixing of the blocks of different stiffness and orientational ordering of the stiff blocks. We observe dumbbell-like morphologies, lamellar phases, and for the larger block lengths also Saturn-like structures with a core of flexible segments and the stiff segments forming a ring around the core.

On the Pseudo Phase Diagram of Single Semi-Flexible Polymer Chains: A Flat-Histogram Monte Carlo Study

“…Noting that the pseudo phase diagrams are also chain length dependent, it is apparent that there exists a huge variety of possible collapse and folding behaviors to non-trivial morphologies resulting from the competition between chain stiffness and monomer attraction. Going beyond the homopolymer case [37,38] introduces further complexity on the path to protein-like polymers, for which the native state in addition is stabilized by specific interactions like, e.g., hydrogen bonds.…”

“…We have performed Stochastic Approximation Monte Carlo simulations (SAMC) [33,34], a version of flat-histogram Monte Carlo simulations [35], which we adapted to the simulation of polymer models [36,37,38]. These simulations determine a numerically exact (if the simulation is converged sufficiently) result for the density of states, g(E), of the model under study, or, more precisely, its logarithm, which is the micro-canonical entropy, S(E)=prefixln[g(E)], where we set kB=1.…”

Diagrams of States of Single Flexible-Semiflexible Multi-Block Copolymer Chains: A Flat-Histogram Monte Carlo Study

“…As in our previous study of a single SF-copolymer chain in a non-selective solvent [9], we considered an off-lattice model of a chain with length N=64, where monomer units were hard spheres with diameter σ=1. The bond length l between adjacent monomer units (beads) can vary freely within the range [0.8σ;1.25σ], i.e., there was no elastic energy on the bond length and bonded beads were allowed to interpenetrate.…”

“…These three interaction parameters are related to each other according to Lorentz–Berthelot combining rules, i.e., |εsf|=|εss|·|εff|. The case of the non-selective implicit solvent (εss=εff=εsf=ε) for this model has been studied earlier in [9,10,11].…”

“…As has been shown by means of computer simulations, even such a simple system as a single flexible-semiflexible macromolecule, i.e., a single multiblock-copolymer chain consisting of equal amounts of Flexible (F) and Semiflexible (S) blocks, without any specific interactions in a non-selective solvent (i.e., a solvent with equal affinity to monomer units of S- and F-types), demonstrates a complicated phase behavior [9,10,11]. In the present work, we perform a similar study for the case of a selective solvent (i.e., an implicit solvent that has different affinity to monomer units of types F and S) with the goal to obtain single chain diagrams of states (pseudo-phase diagrams).…”