Dynamics of molecules adsorbed on a die wall during polymer melt extrusion

A new, quantitative model to describe the dynamics of polymer molecules grafted on a solid wall is presented. This model is based on the bond vector probability distribution function (BVPDF) which contains the necessary information about the spatial conformations of the grafted chains. All macroscopic quantities of practical interest such as wall shear stress are shown to follow from second moments of the BVPDF. The derived equation of motion for the BVPDF takes into account all important mechanisms on the grafted chain such as retraction, convection, and (convective) constraint release. The proposed model can further be used to derive the quantitative stick-slip law given the molecular and wall surface parameters.