Optothermal pulling, trapping, and assembly of colloids using nanowire plasmons

TL;DR

This study demonstrates how nanowire surface plasmon polaritons can be used to optothermally pull, trap, and assemble colloids, revealing polarization-sensitive effects and potential applications in active matter systems.

Contribution

It provides the first experimental analysis of SPPs-driven optothermal manipulation of colloids, including polarization effects and multi-particle assembly.

Findings

Colloids are directionally pulled towards nanowire excitation points.

Colloids are trapped and assembled around the nanowire via thermophoresis.

Assembly is sensitive to excitation polarization, confirmed by temperature simulations.

Abstract

Optical excitation of colloids can be harnessed to realize soft matter systems that are out of equilibrium. In this paper, we present our experimental studies on the dynamics of silica colloids in the vicinity of a silver nanowire propagating surface plasmon polaritons (SPPs). Due to the optothermal interaction, the colloids are directionally pulled towards the excitation point of the nanowire. Having reached this point, they are spatio-temporally trapped around the excitation location. By increasing the concentration of colloids in the system, we observe multi-particle assembly around the nanowire. This process is thermophoretically driven and assisted by SPPs. Furthermore, we find such an assembly to be sensitive to the excitation polarization at input of the nanowire. Numerically-simulated temperature distribution around an illuminated nanowire corroborates sensitivity to the excitation polarization. Our study will find relevance in exploration of SPPs-assisted optothermal pulling, trapping and assembly of colloids, and can serve as test-beds of plasmon-driven active matter.