Rheology of polymer solutions using colloidal-probe atomic force microscopy

Abstract

We use colloidal-probe atomic force microscope (AFM) to study the rheological behavior of polymer solutions confined between two surfaces: the surface of a sphere and a flat surface on which the fluid is deposited. Measurements of the hydrodynamic force exerted on the sphere by the flowing liquid allowed retrieving the viscosity of the solution for different distances between the sphere and the flat surface. This method has been experimentally tested for Newtonian fluids for which the viscosity does not vary versus the gap dimensions. On the other hand, for non-Newtonian fluids, such as the large molecular weight polymer solutions used here, the measured viscosity depends on the gap height D between the flat surface and the sphere. The decrease of the viscosity versus gap height is similar to previously observed variations in colloidal suspensions. Depletion of polymers in the gap region due to the high shear rates involved is a possible cause for such a variation.

Dynamic stabilisation during the drainage of thin film polymer solutions

“…A Pe number of O(10 2 -10 3 ) was calculated for DP Z 400 Pa. Apart from the larger DM w that can be attained if bimodal solutions exhibit concentration gradients, the dynamic stabilisation could also be facilitated by the fact that larger molecules experience a stronger drag force during drainage, which could potentially result in a more pronounced depletion from the film. 29,110 Another estimate can be done regarding the magnitude of the concentration differences inside the film. Assuming that thickness corrugations will develop when DP osm B 2s/R, 37 a Dc B 10% can be estimated from eqn (8) for the solution of the medium M w polymer (ESI †).…”

Axisymmetric Stokes flow due to a point-force singularity acting between two coaxially positioned rigid no-slip disks

“…A deep understanding of the nature of the mutual interactions between particles and their confining interfaces is of crucial importance in guiding the design of devices and tools for an optimal nanoscale control of biological macromolecules. Notable examples include single-molecule manipulation (Turner et al 1998;Campbell et al 2004), DNA mapping for genomic applications (Reisner et al 2005;Riehn et al 2005;Persson & Tegenfeldt 2010), DNA separation and sorting (Doyle et al 2002;Cross, Strychalski & Craighead 2007;Xia, Yan & Hou 2012), and rheological probing of complex structures using atomic force microscopy cantilevers (François et al 2008(François et al , 2009Dufour et al 2012;Darwiche et al 2013).…”

Linear response functions of an electrolyte solution in a uniform flow

“…For the same ionic concentration of the aqueous solution above, the velocity u 0 100 µm/s is obtained. Velocities of order 100 µm/s are accessible in experiments and have been used in colloidal-probe AFM measurements [33][34][35] as the relative velocity between probe and object.…”