Chiral patterns arising from electrostatic growth models

TL;DR

This paper presents a mechanism for the emergence of chiral growth patterns in clusters formed from achiral molecules, driven by electrostatic effects, which explains observed seahorse-like shapes without microscopic chirality.

Contribution

It introduces a novel electrostatic growth model that explains spontaneous chiral symmetry breaking in achiral molecular clusters, supported by continuum and Monte Carlo simulations.

Findings

Continuum model exhibits spontaneous chiral symmetry breaking.

Finned 'S'-shaped patterns resemble experimental observations.

Electrostatic effects can induce chiral morphologies without microscopic chirality.

Abstract

Recently, unusual and strikingly beautiful seahorse-like growth patterns have been observed under conditions of quasi-two-dimensional growth. These `S'-shaped patterns strongly break two-dimensional inversion symmetry; however such broken symmetry occurs only at the level of overall morphology, as the clusters are formed from achiral molecules with an achiral unit cell. Here we describe a mechanism which gives rise to chiral growth morphologies without invoking microscopic chirality. This mechanism involves trapped electrostatic charge on the growing cluster, and the enhancement of growth in regions of large electric field. We illustrate the mechanism with a tree growth model, with a continuum model for the motion of the one-dimensional boundary, and with microscopic Monte Carlo simulations. Our most dramatic results are found using the continuum model, which strongly exhibits spontaneous chiral symmetry breaking, and in particular finned `S' shapes like those seen in the experiments.