Viscosity and Normal Stress Coefficients of a Critical Gel
Abstract
Polycondensates close to the gel point display non-Newtonian behavior, with a shear-rate dependent viscosity and non-zero normal stress differences. At the critical point, these material properties diverge, in a way which seems to be universal. We will present the results of simulations of a model intended to describe the gelation transition in soft materials. We have modelled a gel as a randomly cross-linked network, built from a lattice of soft spheres. A fraction p of nearest-neighbor pairs are bonded, using a harmonic spring. The clusters formed are thus identical to those studied in percolation theory, and their geometric properties and critical point are known. We then simulate planar Couette flow using non-equilibrium molecular dynamics. This makes it possible to calculate the shear rate dependence of the viscosity, as well as the normal stress differences. The divergence of these quantities at the critical probability pc for percolation has been calculated and compares well with similar calculations using equilibrium methods, where this comparison is possible.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2004
- Bibcode:
- 2004APS..MARN29003V