Slip of gels in colloid-polymer mixtures under shear

We investigate the time-dependent rheology and slip behaviour of colloidal gels formed under polymer-induced depletion attraction. The shape of the flow curves at low applied shear rates is suggestive of slip, which we confirm using confocal imaging. Time-dependent linear viscoelastic measurements show an unexpected drop of the elastic modulus below the viscous one after a critical time. We present a dynamic phase diagram characterizing the dependence of slip on polymer concentration and colloid volume fraction. Confocal imaging links slip to the restructuring of clusters with time, which leads to a reduction of the number of contacts between the colloidal network and the rheometer surfaces. Such behaviour is shear rate dependent and correlated to changes in the gel structure, which changed from independent small aggregates at high shear rates to percolated clusters at low shear rates.