Simulation of shear wave propagation in gelling systems

• Main Author: Jones, R. A.
• Published: Swansea University 2003
• Subjects: 530.0724
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637714

Conventional, forced, non-resonant oscillatory rheometers can possess limitations in the measurement of some gels, where they display a pronounced mechanical weakness, are highly shear sensitive and exhibit marked time dependence. Instead, shear wave propagation techniques are proposed as one alternative. One instrument that employs shear wave propagation techniques in the determination of the dynamic shear moduli, G' and G", is the Pulse Resonance Rheometer. The Pulse Resonance Rheometer uses two modes of operation, measurements of the velocity of pulse propagation and measurements of the resonant bandwidth. This thesis uses computer simulations to determine the errors inherent the in use of a pulse velocity to calculate the dynamic moduli of a gel at the gel point, and also a pre gel point viscoelastic liquid. It compares these results to the measurements from simulations of groups and a corresponding group velocity as an inherently more accurate method of gel point determination. The simulations at gel point are carried out using constitutive equations that result from the Winter and Chambon criteria. Simulations are carried out for the pre gel point viscoelastic liquid using the Gross-Marvin ladder model to mimic the development of the gel network. A fractal dimension can be found to be associated with this build up of the network, with different fractal dimensions corresponding to different types of Winter-Chambon gel that are characterised by the viscoelastic exponent a.