Assembling of three-dimensional crystals by large nonequilibrium depletion force

TL;DR

This paper introduces a novel method to assemble defect-free three-dimensional colloidal crystals using a large nonequilibrium depletion force driven by thermophoresis, with potential applications in photonics and biophysics.

Contribution

The study demonstrates a new approach to achieve large effective Soret coefficients in colloids, enabling rapid and defect-free 3D crystal assembly through thermophoretic manipulation.

Findings

Successful formation of defect-free colloidal photonic crystals

Large nonequilibrium depletion force driven by thermophoresis

Potential applications in biophysics and low-cost fabrication

Abstract

We propose and demonstrate a method to achieve large effective Soret coefficient in colloids by suitably mixing two different particles, e.g., silica beads and Fe3O4 nanoparticles. It is shown that the thermophoretic motion of Fe3O4 nanoparticles out of the heating region results in a large nonequlibrium depletion force for silica beads. Consequently, silica beads are driven quickly to the heating region, forming a three-dimensional crystal with few defects and dislocations. The binding of silica beads is so tight that a colloidal photonic crystal can be achieved after the complete evaporation of solvent, water. Thus, for fabrication of defect free colloidal PCs, periodic structures for molecular sieves, among others, the proposed technique could be a low cost alternative. In addition as we use biocompatible materials, this technique could be a tool for biophysics studies where the potential of large effective Soret coefficient could be useful.