Plastic Deformation of Glassy Polymers: Correlation Between Shear Activation Volume and Entanglement Density
- PDF / 83,236 Bytes
- 6 Pages / 595 x 842 pts (A4) Page_size
- 35 Downloads / 199 Views
B3.3.1
Plastic Deformation of Glassy Polymers: Correlation Between Shear Activation Volume and Entanglement Density Janet Ho, Leon Govaert1 , and Marcel Utz Institute of Materials Science, University of Connecticut, Storrs, CT 06269, U.S.A. 1 Dutch Polymer Institute (DPI), Eindhoven University of Technology, Eindhoven, The Netherlands. ABSTRACT The shear activation volumes of miscible polystyrene-poly(2,6-dimethyl-1,4-phenylene oxide) (PS-PPO) blends at different PS-PPO ratios were determined experimentally by both plane strain and uniaxial compression at constant strain rates. We find that the same correlation between the shear activation volume Veq and the entanglement density ρe holds for the blend as well as for various pure glassy polymers: Veq ∝ ρe 0 6 . Since the shear activation volume is closely related to the size of the plastic shear zones, this correlation suggests that the cooperativity of the elementary processes of plastic deformation in glassy polymers scales with the entanglement density. INTRODUCTION Plastic deformation in glassy polymers is not yet fully understood, even though many phenomenological models that describe accurately the behavior of plastic deformation in polymer glasses do exist [1–5]. Much evidence based on atomistic computer simulation studies [6–9] and calorimetric experiments [10, 11] indicates that plastic deformation in glassy materials is the result of repeated nucleation of stress-relaxation events, which lead to irreversible cooperative rearrangements of molecular segments. These stress-relaxation events, which are called shear transformations, are sessile, and the rate of plastic deformation in glassy polymers is controlled by the nucleation of shear transformations rather than by their mobility [1]. The size of the regions in which the shear transformations take place is a key parameter for understanding the plasticity in glassy solids at a molecular level. For polymer glasses, the length scale of these plastic shear zones (PSZs) [1] is unknown, as are the molecular parameters that control it. The goal of the present work is to explore the influence of entanglement density [12] on the shear activation volume. For this purpose, we have focused on the well known miscible polystyrene-poly(2,6-dimethyl-1,4-phenylene oxide) (PS-PPO) polymer blend system [13]. This blend is miscible at all compositions, and the entanglement densities can be adjusted by varying the composition continuously [14]. The shear activation volumes at different PS-PPO ratios were determined experimentally. A correlation between the shear activation volumes and the entanglement densities of this blend and of various pure glassy polymers is demonstrated. Since the shear activation volume is closely related to the size of a PSZ, our result suggests that the length scale of the elementary processes of plastic deformation is set by the entanglement density.
B3.3.2
THEORY A theoretical framework for plastic deformation in glassy polymers can be formulated by considering the change in the total energy of
Data Loading...
