Shear-induced order and rotation in pipe flow of short-chain molecules

In a series of molecular-dynamics simulations, oligomer fluids undergoing Poiseuille (pipe) flow are shown to experience rotational motion and mean orientation that is dependent on the local shear rate. Local molecular alignment is found to reflect the competition between the Maxwell forty-five degree prediction and a preferred orientation parallel to the flow close to the boundary. The molecules, each consisting of four linked hard spheres, and both fully flexible and semi-rigid chains are studied, the flow is driven by a uniform field, with the pipe walls serving both as non-slip boundaries and thermal sinks for the shear-generated heat.