Phase separation in soft repulsive polymer mixtures: foundation and implication for chromatin organization.

Given the wide range of length scales, the analysis of polymer systems often requires coarse-graining, for which various levels of description may be possible depending on the phenomenon under consideration. Here, we provide a super-coarse grained description, where polymers are represented as a succession of mesosopic soft beads which are allowed to overlap with others. We then investigate the phase separation behaviors in a mixture of such homopolymers based on mean-field theory, and discuss universal aspects of the miscibility phase diagram in comparison with the numerical simulation.

Charge block-driven liquid-liquid phase separation - mechanism and biological roles.

Liquid-liquid phase separation (LLPS) has increasingly been found to play pivotal roles in a number of intracellular events and reactions, and has introduced a new paradigm in cell biology to explain protein-protein and enzyme-ligand interactions beyond conventional molecular and biochemical theories. LLPS is driven by the cumulative effects of weak and promiscuous interactions, including electrostatic, hydrophobic and cation-π interactions, among polypeptides containing intrinsically disordered regions (IDRs) and describes the macroscopic behaviours of IDR-containing proteins in an intracellular milieu. Recent studies have revealed that interactions between 'charge blocks' - clusters of like charges along the polypeptide chain - strongly induce LLPS and play fundamental roles in its spatiotemporal regulation.

Conducting transition analysis of thin films composed of long flexible macromolecules: Percolation study.

By simulating percolation and critical phenomena of labelled species inside films composed of single-component linear homogeneous macromolecules using the molecular Monte Carlo method in 3 dimensions, we study the dependence of these conducting transition and critical phenomena upon both thermal movements, i.e. spontaneous mobility, and extra-molecular topological constraints of the molecules.

Particle Monte Carlo simulation of string-like colloidal assembly in two and three dimensions.

We simulate structural phase behavior of polymer-grafted colloidal particles by molecular Monte Carlo technique. The interparticle potential, which has a finite repulsive square-step outside a rigid core of the colloid, was previously confirmed via numerical self-consistent field calculation. This model potential is purely repulsive.

Measuring excess free energies of self-assembled membrane structures.

Using computer simulation of a solvent-free, coarse-grained model for amphiphilic membranes, we study the excess free energy of hourglass-shaped connections (i.e., stalks) between two apposed bilayer membranes.

Computing free energies of interfaces in self-assembling systems.

Using molecular simulation of a coarse-grained model for a symmetric diblock copolymer melt, we calculate the free energy of interfaces between lamellar morphologies with different orientations. Two examples are considered: (a) a T-junction between two lamellar structures with perpendicular orientation and (b) a surface reconstruction that arises when lamella-forming diblock copolymers assemble on a stripe-patterned surface, where the pattern period is significantly larger than the lamellar spacing in the bulk. The computational scheme relies on reversibly relating the defect structure to a reference state by an external ordering field.