A. Sauret, E. C. Barney, A. Perro, E. Villermaux, H. A. Stone and E. Dressaire 

Applied Physics Letters 2014, 105, 074101 

We report on a microfluidic method that allows measurement of a small concentration of largecontaminants in suspensions of solid micrometer-scale particles. To perform the measurement, we flowthe colloidalsuspension through a series of constrictions, i.e., a microchannel of varying cross-section. We show and quantify the role of large contaminants in the formation of clogs at a constriction and the growth of the resulting filter cake. By measuring the time interval between two clogging events in an array of parallel microchannels, we are able to estimate the concentration of contaminants whose size is selected by the geometry of the microfluidic device. This technique for characterizing colloidalsuspensions offers a versatile and rapid tool to explore the role of contaminants on the properties of thesuspensions.