Abstract
When asymmetric Janus micromotors are immobilized on a surface, they act as chemically powered micropumps, turning chemical energy from the fluid into a bulk flow. However, such pumps have previously produced only localized recirculating flows, which cannot be used to pump fluid in one direction. Here, we demonstrate that an array of three-dimensional, photochemically active Au/TiO2 Janus pillars can pump water. Upon UV illumination, a water-splitting reaction rapidly creates a directional bulk flow above the active surface. By lining a 2D microchannel with such active surfaces, various flow profiles are created within the channels. Analytical and numerical models of a channel with active surfaces predict flow profiles that agree very well with the experimental results. The light-driven active surfaces provide a way to wirelessly pump fluids at small scales and could be used for real-time, localized flow control in complex microfluidic networks.
Highlights
When asymmetric Janus micromotors are immobilized on a surface, they act as chemically powered micropumps, turning chemical energy from the fluid into a bulk flow
We show that a simple fluid dynamic model of an active channel, in which the active surface provides a wall-slip velocity, can accurately describe the experimentally measured flow profiles within the channel
After removing the photoresist and annealing the sample, a regular array of TiO2−Au Janus pillars are left on the substrate
Summary
When asymmetric Janus micromotors are immobilized on a surface, they act as chemically powered micropumps, turning chemical energy from the fluid into a bulk flow. Such pumps have previously produced only localized recirculating flows, which cannot be used to pump fluid in one direction. The light-driven active surfaces provide a way to wirelessly pump fluids at small scales and could be used for real-time, localized flow control in complex microfluidic networks. The pillars promote water splitting when irradiated with UV light, leading to local osmotic flows around the pillars The ensemble of these localized flows generate an effective wall-slip that drives a bulk flow in the channel. The results suggest that this architecture would scale down well to smaller scales, where it could enable finely tuned control over complex micro- and nanofluidic networks
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