Flow with slip at the wall: from simple to complex fluids

We present series of experiments based on a Near Field Laser Velocimetry technique, aimed to characterize friction mechanisms at fluid–solid interfaces. For simple fluids, we show that noticeable slip at the wall can occur in the case of a smooth surface even in total wetting conditions. For polymer fluids, entanglements between surface anchored chains and bulk polymer govern the friction. A dynamical decoupling associated to disentanglements between surface and bulk chains is observed at large enough shear rates, leading to high slip and low friction. More elastomer like polymers lead to stick–slip instabilities in a narrow range of shear rates.