Electro-Thermo-Plasmonic Flow in Gold Nanoparticle Suspensions: Nonlinear Flow Velocity Dependence with Aggregates Concentration

TL;DR

This study investigates how electro-thermal flow in gold nanoparticle suspensions depends nonlinearly on particle concentration, combining experiments and simulations to understand aggregation effects and optimize microscale liquid mixing.

Contribution

It provides a combined experimental and simulation analysis of electro-thermal flow in nanoparticle suspensions, highlighting nonlinear velocity dependence due to aggregation effects.

Findings

Flow velocity shows nonlinear dependence on particle concentration.

Aggregates of 5-9 gold nanoparticles enhance absorption and flow.

Simulations align with experimental observations of aggregation effects.

Abstract

Efficient mixing and pumping of liquids at the microscale is a technology that is still to be optimized. The combination of an AC electric field with a small temperature gradient leads to a strong electro-thermal flow that can be used for multiple purposes. Combining simulations and experiments, an analysis of the performance of electro-thermal flow is provided when the temperature gradient is generated by illuminating plasmonic nanoparticles in suspension with a near-resonance focused laser. Fluid flow is measured by tracking the velocity of fluorescent tracer microparticles in suspension as a function of the electric field, laser power, and concentration of plasmonic particles. Among other results, a non-linear relationship is found between the velocity of the fluid and particle concentration, which is justified in terms of multiple scattering-absorption events, involving aggregates and individual particles, that lead to enhanced absorption when the concentration is raised. Simulations provide a description of the phenomenon that is compatible with experiments and constitute a way to understand and estimate the absorption and scattering cross-sections of dispersed particles and/or aggregates. A comparison of experiments and simulations suggests that the gold nanoparticles are aggregated forming clusters of about 5-9 particles, but no information about their structure cannot be obtained without further theoretical and experimental developments. This nonlinear behavior could be useful to get very high ETP velocities by inducing some controlled aggregation of the particles.