Chain-Exchange Dynamics at a Polymer−Solid Interface: effects of Polydispersity and Shear Stress on Linear Low-Density Polyethylene Flow

Abstract

Polymer−surface interactions in flowing systems were studied using an attenuated total reflectance Fourier transform infrared spectroscopy technique. The absorbance of deuterated polyethylene, d-PE66 (Mw = 6.60 × 104) and d-PE112 (Mw = 1.12 × 105), near the surface of a flat zinc selenide crystal was followed as it was replaced by linear low-density polyethylene (Mw = 1.07 × 105). The experiments were performed under wall stresses of 0.090, 0.134, and 0.155 MPa using a rectangular flow channel formed by a ZnSe crystal and an aluminum block. The decay profiles depended on the molecular weight distribution, the chemical composition distribution, and the shear stress. For d-PE112, the decay profiles suggest that slip is due to a cohesive failure. For d-PE66, the slip mechanism appeared to be due to adhesive failure. For d-PE112 with larger and regular chains, an immobile layer forms whose thickness (12−17 nm) depended on the wall shear stress.