The rheological behaviour of suspensions of fat particles in oil interpreted in terms of a transient-network model

The transient-network model for concentrated dispersions, described in a previous paper, is used to describe the rheological behaviour of dispersions of glyceryl tristearate crystals in paraffin oil. The model prediction of the storage modulus of this system is compared with corresponding expressions given in literature. Model calculations are carried out to fit the linear viscoelastic behaviour of the system as well as its stress response in large amplitude shear experiments. Information is thus obtained about the stiffness and strength of the interparticle bonds, and the chance of them breaking in a state of rest or as the result of flow. It is concluded that the probability of interparticle bond fracture strongly depends on the measure of bond stretching. The general findings link up with the Lennard-Jones potential which is assumed to describe the potential energy of the bonds between the particles. Accurate measurements of the temperature dependence of the dynamic moduli by making use of a torsion resonator lead to the conclusion that the energy dissipation at a high frequency originates mainly from the flow of liquid around the particles

A transient-network model describing the rheological behaviour of concentrated dispersions

Attractive forces acting between particles in dispersions may cause a three-dimensional structure to be built up. A temporary-network model is postulated that describes the rheological behaviour of such systems. Chains of particles are assumed to be created and broken by thermal actions and by applied deformation. The relation between the network structure and the macroscopic stress tensor is deduced. One of the main model features is that no use is made of the common assumption of affinity of the motion of the chain vectors with the gradient of the macroscopic velocity field. Instead, the chain deformations are assumed to depend on the forces acting on them, i.e. their deformations depend on their stiffness and on the applied deformation, whereas fracture of chains may cause stress relaxation in the rest of the network. The chains may behave as highly non-linear springs, whereas the probability that the chains will break in some time interval may be an explicit function of the chain length itself. Integral equations are derived, from which the stress-tensor components can be calculated in any flow experiment, that obeys creeping-flow conditions. Analytical expressions are obtained for the relaxation spectrum of such systems in terms of the microscopic parameters

The squeezing of liquid out of a structured dispersion

The equations predicting the rate of liquid removal out of a structured dispersion that is unilaterally compressed are presented in a nondimensional form. The dispersed particles, mostly solid and of colloidal dimensions, are assumed to compose a transient three-dimensional network. This letter refers to a previous paper in which the original equations, i.e., without being non-dimensionalized, were applied to calculate the rate of oil removal out of a dispersion of fat partciles under unilateral compression

The relation between the permeability of structured dispersions and the viscoelastic properties of the dispersed phase

It is shown that not only the average particle size and compression modulus, but also the viscoelastic properties of the network affect the rate of liquid removal out of a concentrated disperse system that is unilaterally compressed. A Maxwell-like constitutive equation is introduced to express these viscoelastic properties. The rate of liquid removal is calculated for a set of values of the elastic modulus and the time constant that appear in the constitutive equation. It is shown that permeability measurements on concentrated fat dispersions can be interpreted in terms of network properties also when the network is viscoelastic, i.e., it is assumed that processes take place inside the network that involve energy dissipation