On the limit of linear viscoelastic response in the flow between eccentric rotating disks

The dependence on frequency of the limiting value of strain, ΨL, for which linear Viscoelastic response occurs in eccentric rotating disks (ERD) flow is studied theoretically and experimentally. The theoretical investigations are based upon the general simple-fluid theory of Coleman and Noll. It is shown that according to this theory ΨL becomes independent of angular velocity, ω, at relatively high frequencies, whereas ΨL becomes inversely proportional to at sufficiently low frequencies. The results of previous investigations, based upon some special rheological models, are discussed. The behavior predicted by the simple-fluid theory is confirmed by experiments on polyisobutylene solutions

Linear viscoelasticity of emulsions : II. Measurements of the linear viscoelastic behavior of emulsions in the kilohertz range

Linear viscoelasticity of emulsions in shear deformation in the kilohertz range is demonstrated experimentally. In order to avoid complications due to inertia effects, emulsions with small droplet sizes are studied. The preliminary measurements are interpreted as being the result of droplet deformations. If this interpretation is correct, measurements of the dynamic viscosity of emulsions may be used to obtain information about the mechanical properties of the interfacial layer between droplets and the continuous phase. In particular, the evaluation of the interfacial tension of emulsion droplets from bulk properties might be possible using this technique

Frequency dependent linear viscoelastic properties of ordered polystyrene latices

An experimental investigation of linear rheological properties of monodisperse ordered latex dispersions has been carried out. Measurements of the dynamic shear modulus and the dynamic viscosity in the frequency range between 0.04 Hz and 2500 Hz are reported. The volume fraction and the electrolyte concentration were variables in the experiment. The results show that a description of the rheological behaviour with a simple linear phenomenological equation is not possible. The measured dynamic moduli can only be described with a great number of relaxation times

Rheology of suspensions stabilized by long grafted polymers

The synthesis of colloidal silica spheres grafted with long poly-(dimethyl siloxane) chains as described in literature has been successfully reproduced. The particles have been elaborately characterized, using different techniques and taking advantage of the availability of the unreacted bare particles and free polymer. Rheological measurements were performed on dispersions in heptane, all made from a single stock. An effective volume fraction was defined, based on the viscosity at low concentrations. Low shear viscosities and linear viscoelastic properties were measured at effective volume fractions up to 0.81. A transition from liquid-like to solid-like behavior is observed at φ ≅ 0.60. Up to this volume fraction, the particles behave much like Brownian hard spheres. At higher concentrations, softness effects become noticeable. Here, also differences from otherwise comparable soft spheres become pronounced