Phase behavior of blocky charge lattice polymers: Crystals, liquids, sheets, filaments and clusters

TL;DR

This study uses lattice Monte Carlo simulations to explore how charge patterning influences phase separation in polymers, revealing diverse states like crystals, liquids, and clusters, with implications for understanding intrinsically disordered proteins.

Contribution

It systematically analyzes the phase behavior of charge-patterned polymers, highlighting the impact of sequence and charge density on their condensed states, including liquid-like droplets.

Findings

Three sequences form crystals at low temperatures.

One sequence exhibits clear liquid behavior.

Long neutral patches limit structure size and shape.

Abstract

Motivated by the idea that intrinsically disordered proteins (IDPs) condense into liquid-like droplets within cells, we carry out Monte Carlo simulations of a polymer lattice model to study the relationship between charge patterning and phase separation. Polymer chains containing neutral, positively charged and negatively charged monomers are placed on a cubic lattice. Only nearest neighbor interactions between charges are considered. We determine the phase diagram for a systematically varied set of sequences. We observe homogeneous fluids, liquid condensation, cluster phases, filaments, and crystal states. Of the six sequences we study, three form crystals at low temperatures. The other three sequences, which have lower charge densities, instead collapse into gel-like networks or unconnected finite clusters. Longer neutral patches along the sequence sterically limit the size and shape of low-energy structures, which is analogous to the effect of charge or limited valence in attractive colloids. Only one sequence clearly exhibits liquid behavior; this sequence has a reduced tendency to individually fold and crystallize compared to others of similar charge density and draws parallels to real IDP behavior.