Fri, 25 Jul 2008 04:35:03 BST CiteULike: dchens Furst http://www.citeulike.org/user/dchen/author/Furst CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/dchen/article/2880278 <i>Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 76, No. 5. (2007)</i><br /><br />We present the behavior of depletion-induced gels for vesicle-polymer mixtures when the ratio of the polymer radius of gyration to the mean vesicle radius is 0.09 and 0.27. As the polymer concentration increases, density gradients build up and an interface is developed between a highly turbid vesicle-rich phase and a polymer-rich phase. Increasing the polymer concentration further forms a gel (CP=0.3 and 0.1  wt  % for Rg/a0.09 and 0.27, respectively), which subsequently collapses. This collapse is characterized by a slow initial rising for a finite delay time, a rapid collapse, and a slow final compaction to an equilibrium height. However, we observe a remarkably different polymer concentration dependence on the collapse rate. Unlike other colloidal gels, we find that the delay time for the vesicle collapse decreases with increasing polymer concentration. We show that this behavior can be accounted for by considering the permeability for solvent backflow, which is directly related to the characteristic pore area of the gel obtained using confocal microscopy. Microscopic structure and collapse of depletion-induced gels in vesicle-polymer mixtures Ji Huh Matthew Lynch Eric Furst doi:10.1103/PhysRevE.76.051409 Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 76, No. 5. (2007) 2008-06-10T16:41:03-00:00 2007 Physical Review E (Statistical, Nonlinear, and Soft Matter Physics) 76 5 APS 2007 depletion gel polymer pre vesicle http://www.citeulike.org/user/dchen/article/2730851 <i>Journal of Rheology, Vol. 50, No. 1. (2006), pp. 77-92.</i><br /><br />The microrheology of a colloidal suspension is measured using laser tweezers. Suspensions of refractive index-matched fluorinated ethylene propylene (FEP) particles are seeded with index-mismatched polystyrene or silica probe particles. Laser trapped probes are then subjected to steady uniform flows, enabling measurements of the suspension microviscosity as a function of FEP volume fraction and flow velocity. The microrheology results agree with bulk rheology, and both exhibit the same volume fraction dependence of the Krieger-Dougherty relationship for hard spheres. As volume fraction increases, the microrheology more closely agrees with the infinite shear bulk viscosity. In this regime, measurements using small probes exhibit additional shear thinning. Using confocal microscopy and fluorescent poly(methylmethacrylate) dispersions, we demonstrate that the nonlinear microrheology is consistent with the development of an anisotropic nonequilibrium pair distribution function between the probe and bath particles, with a denser region at the leading surface of the probe and a wake trailing it. The nonlinear response and underlying microstructure are in qualitative agreement with recent theory [T. M. Squires and J. F. Brady, Phys. Fluids 17, 073101 (2005)]. ©2006 The Society of Rheology Laser tweezer microrheology of a colloidal suspension Alexander Meyer Andrew Marshall Brian Bush Eric Furst doi:10.1122/1.2139098 Journal of Rheology, Vol. 50, No. 1. (2006), pp. 77-92. 2008-04-28T19:22:56-00:00 2006 Journal of Rheology 50 1 77 92 SOR colloids microrheology opticaltweezer technique