In situ measurement of crystalline lattice strains in phase IV polytetrafluoroethylene

Abstract

Measurements of crystalline lattice strain development during deformation of polytetrafluoroethylene (PTFE) have been performed utilizing neutron diffraction measurements at the SMARTS diffractometer at Los Alamos National Laboratory. The chemical structure of PTFE, (C₂F₄)_n, makes it ideally suited for investigation by neutron methods as it is free of the hydrogen that causes limited penetration depths and poor diffraction acquisition in most polymers. Six primary diffraction peaks have been identified corresponding with deformation planes in the hexagonal unit cell. Deformation perpendicular to the prismatic planes occurs by interpolymer chain compression with a moduli ∼10 × bulk, while deformation perpendicular to the pyramidal planes occurs by interpolymer chain shear with a moduli ∼100–1000 × bulk, and deformation perpendicular to the basal plane occurs by intrapolymer chain compression with a moduli ∼1000 × bulk, corresponding with theoretical values for a PTFE chain modulus.