Deformation and aging of capillary suspension networks

By adding a small amount of immiscible secondary fluid to the continuous phase of a suspension, the rheological behavior of the suspension can change dramatically from a fluid-like to gel-like state or from a weak network into a strong network [1]. This transition is caused by attractive capillary force between the particles and two fluids inducing a sample-spanning network. Thus, this kind of system has been termed as capillary suspension. This effect can even occur when the secondary fluid wets the particles less well than the bulk fluid. In the capillary state, shown in the sketch below, clusters of particles form around the secondary fluid resulting in an energetically favorable state [2]. A model capillary suspension composed of PMMA particles in glycerol with added paraffin oil ( are used in this study. Aging and resistance of the sample network to a very high deformation using a capillary rheometer were investigated. The rheological properties before and after being stressed with high shear rates were compared using linear and nonlinear oscillatory shear measurements. Images from confocal microscope are used to gain insight into the network microstructure of the capillary suspension. The high shear modulus remains after the high shear period, but shear thickening behavior is observed. After several days, the sheared sample retains its strength while the unsheared sample weakens. Literature: [1] E. Koos and N. Willenbacher (2011). Science 331(6019): 897-900. [2] E. Koos and N. Willenbacher (2012). Soft Matter 8(14): 3988-3994.status: publishe