In most situations, drying is accompanied by the development of strong concentration gradients. Here, we evidence theoretically and experimentally that there exist microfluidic geometries for which confined drying becomes homogeneous, i.e., with no concentration gradient regardless of the type of solute involved in the process; ions, molecules, and colloids do concentrate in the same way providing a limited set of assumptions concerning the microfluidic geometry. It thus makes possible the establishment of phase diagrams of multi-component mixtures at the nanoliter scale.
Silicon microcantilevers can be used to measure the rheological properties of complex fluids. In this paper, two different methods will be presented. In the first method, the microcantilever is used to measure the hydrodynamic force exerted by a confined fluid on a sphere that is attached to the microcantilever. In the second method, the measurement of the microcantilever's dynamic spectrum is used to extract the hydrodynamic force exerted by the surrounding fluid on the microcantilever. The originality of the proposed methods lies in the fact that not only may the viscosity of the fluid be measured, but also the fluid's viscoelasticity, that is, both viscous and elastic properties, which are key parameters in the case of complex fluids. In both methods, the use of analytical equations permits the fluid's complex shear modulus to be extracted and expressed as a function of shear stress and/or frequency.
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