Orientational ordering of colloidal dispersions by application of time dependent external forces

TL;DR

This paper introduces methods to align colloidal particles using time-dependent external forces, enabling synchronized motion without particle interactions, with potential applications in material science and colloidal manipulation.

Contribution

The paper presents two novel approaches for orientational alignment of colloids using uniform, time-dependent forces, expanding control techniques in colloidal dispersions.

Findings

Alignment achieved through piecewise constant forcing

Alignment achieved through rotating force

Conditions for successful alignment identified

Abstract

We present a method of organizing incoherent motion of a colloidal suspension to produce synchronized, coherent motion. This method exploits general features of rotational response to time-dependent forcing, and it does not require interaction between the particles. We report two methods of achieving orientational alignment of an ensemble of identical colloids by means of a time-dependent, but spatially uniform forcing: a) a piecewise constant force alternating between two directions and b) a force uniformly rotating about an axis. The physical origin of the forcing may be e.g., sedimentation or electrophoresis. We will demonstrate that these forcing methods achieve alignment both by analyzing the equations of motion and by simulation. We find the conditions guaranteeing alignment, discuss the limitations of these methods, and suggest possible applications. Examples of such forcing include electrophoresis and sedimentation.