Design principles for Bernal spirals and helices with tunable pitch

TL;DR

This paper presents two in silico design strategies for self-assembling helical colloidal structures with tunable pitch, using magnetic and anisotropic interactions, validated by theoretical predictions and simulations.

Contribution

It introduces novel design principles for creating tunable Bernal spirals and helices with controllable pitch through magnetic and anisotropic interactions.

Findings

Helical superstructures with adjustable pitch achieved via magnetic field modulation.

Bernal spirals predicted to self-assemble from anisotropic building blocks.

Longer helices exhibit flexible, hinge-like rearrangements in agreement with experiments.

Abstract

Using the framework of potential energy landscape theory, we describe two in silico designs for self-assembling helical colloidal superstructures based upon dipolar dumbbells and Janus-type building blocks, respectively. Helical superstructures with controllable pitch length are obtained using external magnetic field driven assembly of asymmetric dumbbells involving screened electrostatic as well as magnetic dipolar interactions. The pitch of the helix is tuned by modulating the Debye screening length over an experimentally accessible range. The second design is based on building blocks composed of rigidly linked spheres with short-range anisotropic interactions, which are predicted to self-assemble into Bernal spirals. These spirals are quite flexible, and longer helices undergo rearrangements via cooperative, hinge-like moves, in agreement with experiment.