On-chip characterization of the transport properties of liquids using microfluidic channel-based Brownian microscopy

We report techniques to characterize the transport properties as well as velocity fields of liquids flowing in microchannels. Microscopic particles of a precisely defined diameter are dispersed in a liquid of interest and their cross-stream Brownian motions are analyzed to determine the local Brownian diffusivity, which is in turn a function of the viscosity or mass concentration. We apply the proposed techniques to determine the viscosity and mass diffusivity of mixtures of glycerin and water, which agree well with the literature values. The techniques developed in this work will enable massively parallel characterization of novel liquids and their mixtures as well as in situ performance evaluation of microfluidic devices.