Confined flows of a polymer microgel

• Published in: The European physical journal. E, Soft matter and biological physics Vol. 36; no. 3; p. 30
• Main Authors: Geraud, Baudouin, Bocquet, Lyderic, Barentin, Catherine
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.03.2013; EDP Sciences; EDP Sciences: EPJ
• Subjects: Applied sciences; Biological and Medical Physics; Biophysics; Chemical Sciences; Complex Fluids and Microfluidics; Complex Systems; Engineering Sciences; Exact sciences and technology; Nanotechnology; Organic polymers; Physicochemistry of polymers; Physics; Physics and Astronomy; Polymer Sciences; Properties and characterization; Regular Article; Soft and Granular Matter; Solution and gel properties; Surfaces and Interfaces; Thin Films; Flowing Matter: Liquids and Complex Fluids; Polyelectrolyte; Rheological model; Acrylic acid polymer; Microgel; Polymer; Measurement method; Experimental study; Flow curve; Modeling; Comparative study; Confined space; Rheological properties
• ISSN: 1292-8941; 1292-895X
• DOI: 10.1140/epje/i2013-13030-3

In this paper, we probe the influence of confinement on the flows of a polymer microgel, namely Carbopol. We compare its bulk rheological behavior, measured with a rheometer and well described by a Hershel-Bulkley law, to velocity profiles measured in rough microchannels, obtained with a particle tracking velocimetry technique. We show a strong disagreement between the bulk prediction for the velocity profiles and the measured ones in the microchannels. Velocity profiles in confined conditions are successfully analyzed within the framework of a non-local fluidity model introduced recently (J. Goyon et al. Nature , 454 , 84 (2008)). This allows to determine a cooperativity length ξ , whose order of magnitude compares with the structure size of the microgel. Moreover, we measure flow curves using a rheometer for different gap conditions and also show that this set of data exhibit a strong effect of the confinement on the measured rheological properties. This is again characterized by a typical length of the same order as the cooperativity length scale ξ . We thus evidence confinement effects with two complementary experiments which both give the same typical length for the rearrangements in the flows. Graphical abstract