Monday, 11 October 2004 - 3:30 PM

This presentation is part of : Wineman Symposium

Torque and Normal Force Responses in Glassy Polymers: Evidence for Molecular Structure Effects

Gregory B. McKenna and Anny Flory. Department of Chemical Engineering, Texas Tech University, 8th St. and Canton Ave., Lubbock, TX 79409-3121

Under the assumption that the nearly isochoric torsion of glassy polymers can be treated as incompressible, the mechanical response of a cylinder of such a viscoelastic material below the glass transition temperature consists of a torque response and a normal force response along the axis of the cylinder. In performing stress relaxation experiments on poly(n-alkyl methacrylate)s, the normal force required to keep the constant deformation is compressive and large. Here we examine the molecular origins of the nonlinear response functions. We consider the influence of the secondary, sub-vitreous beta relaxation on the normal force response. This is done by performing experiments on poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate)(PEMA) which both exhibit a beta peak in the loss modulus as a function of temperature located at the same temperature of 10 C and having about the same intensity. A surprising result is that although the torque response for the PMMA is 50% higher than for the PEMA, the normal force response for the PMMA is 20% lower than the normal force response of the PEMA at the experimental temperatures of 45 C and 30 C. Results from polycarbonate and polysulfone which have very weak beta relaxations will also be presented and discussed.

Back to Wineman Symposium
Back to SES Abstracts

Back to The 41st Annual SES Technical Meeting