Thermo-Electro-Mechanics at Individual Particles in Complex Colloidal Systems.

It has been well established that thermoelectric (TE) field can arise from different Soret coefficients of salt ions in the aqueous solution under constant temperature gradient. Despite their high relevance to cellular biology and particle manipulations, understanding and controlling of TE field in complex colloidal systems that involve micro/nanoparticles, salt ions and molecules have remained challenging. In such colloidal systems, the challenge arises from the thermal interactions with charged micro/nanoparticles that distort the TE field around the particles. Herein, we provide a framework for TE field in colloidal suspensions with various ions and surfactants at the single-nanoparticle level. In particular, we reveal the spatial variation of TE field around a dielectric particle under temperature gradient to determine the thermoelectric trapping force on the particle. Our theoretical results on the trapping force predicted from the TE force profile match well with the experimental opto-thermoelectric trapping stiffness of particles in the solutions where the temperature gradient was well-controlled by a laser beam. With their insight into TE field and force in complex systems, our framework and methodology can be extended to engineer the TE field for versatile opto-thermoelectric manipulations of arbitrarily shaped particles with non-uniform surface morphology and to advance the scientific research in cellular biology.