Steady-shear viscosity and transient stress response for elasto-thixotropic fluids

A phenomenological model for dispersed systems which exhibit complex rheological behaviour such as shear and time-dependent viscosity, yield stress, and elasticity is proposed. The model extends the Quemeda model to describe the viscosity function with a structural parameter λ which varies according to different kinetic orders of particle aggregation and segregation. The transient stress response is obtained by solving an instantaneous Maxwell model with an assumed shear modulus functionG of the same form as the viscosity function η. Accuracy of the proposed model is verified experimentally with the results obtained for two oil (creosote)/water emulsions. The model that gives the best fit of experimental data appears to be the one with kinetic ordersn=m=2.     

Effects of salicylate 2-hydroxybenzoate on ionic liquid N-hexadecane-N-methylpyrrolidinium bromide

Surface tension, steady-shear viscosity, and antibacterial activity were investigated when salicylate 2-hydroxybenzoate (NaSal) was added to the micellar solution of N-hexadecane-N-methylpyrrolidinium bromide (C₁₆MPB). It was found that for the mixed system, two flat portions appeared on the surface tension curve with the existence of NaSal in the low-concentration range. The equilibrium contact angle of droplets was decreased with the increase of NaSal concentration. In addition, the steady-shear viscosity abruptly increased with the increase of the concentration of mixture, even if the concentration of NaSal is low. However, this high-viscosity solution exhibited temperature-sensitive property, and white precipitate formation below 18°C. Moreover, the bactericidal capability of C₁₆MPB was affected severely by the mixture of high concentration. All of these features could be attributed to the special interactions between C₁₆MPB and NaSal molecules, among which intramolecular hydrogen bonding of NaSal plays a key role, which have been primely demonstrated by the package of Gaussian09 in this work.     

Visualization of the breakdown of dilute particles gels during steady-shear

A feature of models concerning the rheology of coagulated suspensions is the development of shear planes. An experimental set-up was developed in which we investigated, by visual analysis, whether shear planes really develop in such systems during steady-shear. A transparent coagulated PTFE dispersion was used, in which the refractive indices of the continuous and dispersed phases were matched, for the formation of a gel. Coagulation was effected by adding NaCl to a concentration of 0.5 M. Polystyrene particles were built into the gel structure as tracer particles. During steady-shear the velocities and trajectories of the tracer particles were analyzed by Particle Tracking Velocimetry (PTV). Indeed layers with approximately the same velocity were observed for a coagulated PTFE-gel, during steady-shear. Deviations from rectilinear motion of the tracer particles were observed. These observations correspond with the assumptions of the giant floc model in which the shear is not distributed homogeneously, but limited to certain shear planes. Deviations from rectilinear motion of the tracer particles in a dilute gel correspond with the results found by Folkersma et al. (1998) in which the distance by which a moving particle entrains its neighbours was assumed to be larger at low volume fractions (≈0.1) than at high volume fractions (≈0.4). Received: 7 May 1998 Accepted: 31 August 1998