Micropumps that propel fluids using energy derived from chemical reactions or photothermal effects can regulate the assembly and segregation of microparticles in solution. In both chemical and light-driven micropumps, fluid pumping occurs via three different mechanisms: thermal buoyancy, solutal buoyancy and diffusioosmosis. These pumping mechanisms can operate simultaneously and the combination of two or more mechanisms leads to complex fluid flow patterns that enables dynamic control over the motion of immersed microparticles.
Segregation of different sized microparticles
We demonstrated how light-induced fluid pumps can be harnessed to separate different sized microparticles. A UV light source is used to generate thermal buoyancy driven convective flows in a microchamber that is inclined at an angle with respect to the horizontal axis. Competition between the drag force imposed by this convective fluid flows and the gravitational force acting on the differently sized microparticles gives rise to their spontaneous separation along the bottom of an inclined microchamber.Manna et al, ACS Appl. Mater. Interfaces 11 , 19 (2019)
Kauffman et al, ChemNanoMat 7, 805 (2021)
Independent control over surface and bulk fluid flows
We develop a standalone fluidic device that is driven by light and operates without the need for external electrical or mechanical pumps. The light initiates a photochemical reaction in the solution; the release of chemical energy from the reaction is transduced into the spontaneous motion of the surrounding fluid. The generated flow is driven by two simultaneously occurring mechanisms: solutal buoyancy that controls the motion of the bulk fluid and diffusioosmosis that regulates motion near the bottom of the chamber. Consequently, the bulk and surface fluid flows can be directed independently of one another. We demonstrate that this exceptional degree of spatiotemporal control provides a new method for autonomously transporting different-sized particles in opposite directions within the chamber.Tansi et al, ACS Appl. Mater. Interfaces 13 , 5 (2021)
Effect of self-induced flows on the rates of chemical reactions
Establishing precise control over the rate of chemical reactions has been a long standing goal in the chemical sciences. We examine if the reaction-induced pumping accelerates the chemical reaction by transporting the reactants to the catalyst at a rate faster than passive diffusion. Using both simulations and experiments, we show a significant increase in reaction rate when reaction-generated convective flow is present.Manna et al, Langmuir 38, 4, (2022)
