https://pure.tue.nl/ws/files/2354845/621626.pdf

Viscoelastic properties of concentrated shear-thickening dispersions

Rheological properties of dome lavas: Case study of Unzen volcano

Influence of sodium salicylate on the rheological behaviour of an aqueous CTAB solution

Block copolymer micelles in the size range between 10 and 100 nm are investigated as model systems for soft spheres The zero shear viscosity η0 and complex modulus G* of micellar solutions are studied via dynamic mechanical spectroscopy and shear viscosity measurements over a wide range of concentrations Depending on their structure, block copolymer micelles exhibit the characteristic rheological behavior of hard spheres, soft spheres, or polymers With increasing concentration, hard-sphere and most soft-sphere samples exhibit a sharp liquid–solid transi-tion as apparent by a divergence of zero shear viscosity η0 and the development of a fre-quency-independent elastic modulus The transition occurs at a certain volume fraction which can be related to the softness of the particles In the solid regime the elastic modulus G exhibits a characteristic concentration dependence which is related to the spatial variation of the soft sphere repulsive potential We observe a G∝Z148r−246 relation between modulus, aggregation number Z and intermicellar distance r which is close to the theoretical prediction G∼Z3/2r−2 of Witten and Pincus derived for polymerically stabilized colloidal particles

Block copolymer micelles: Viscoelasticity and interaction potential of soft spheres

The rheology of a sterically stabilized suspension at high concentration

The viscoelastic properties of concentrated, well dispersed, sterically stabilised polymethyl methacrylate particles were studied using a specially developed low frequency, controlled shear stress rheometer. The experimental results show a well defined viscoelastic transition over a narrow frequency range. Evidence is produced to show that the particles act as hard, non-interacting spheres. It is argued that the transition represents a change from a randomly packed assemblage with particle motion dominated by Browniandiffusion processes to a lower packing density shear flow regime.

The viscoelastic properties of concentrated suspensions

Data on the rheological properties of the hexadecyl-trimethylammonium salicylate system (CTAB-SA) in water are reported. Three concentrations were used (0.1, 0.01, and 0.001 M). For the highest concentration, the effect of temperature on the rheology was studied in detail. The rheology of the 0.1 M CTAB-SA solution indicates a very uniform micellar size. By contrast with concentrated polymethyl methycrylate dispersions studied by the author, there was a strong divergence between the viscosity-shear rate and viscosity-frequency data, although the plateau low shear rate and frequency values agreed over a wide range of temperature. This effect could be explained by a shear rate dependent diffusion constant. The large temperature variation of the plateau viscosity and elasticity modulus values could be explained by a combination of micellar number concentration and flexibility changes as the temperature varies. At lower concentrations, the rheological data shows evidence of polydispersity in micellar size. Strong shear thickening and extensional viscosity effects are also evident, probably due to micellar overlap and cluster formation in strong shear fields and the alignment of the very long micelles in elongational flow. The shear thickening effects take some 200 s to relax (0.01 M solution). Recovery of the elasticity after shearing the 0.1 M solution is rapid (a few hundred milliseconds).

The rheological properties of concentrated cetyltrimethylammonium bromide-salicylic acid solutions in water

The viscoelastic properties of a concentrated 0.6 μm diameter polymethyl methacrylate (pMMA) dispersion, sterically stabilised with a pMMA — polyhydroxystearic acid (pHS) graft copolymer in a hydrocarbon medium, have been measured as a function of concentration at a single fixed frequency (10 Hz) and temperature (23 °C). The measurements were made with a novel viscoelastometer, where the properties of a large (150 g) sample are measured under conditions of minimal disturbance (shear strain and strain rate). The results demonstrate that, in the system measured, small but distinct elastic effects are measurable at concentrations (phase volume fraction) values, where the average particle core separation is considerably in excess of twice the average stabiliser barrier thickness. This finding supports the author's argument that elasticity can arise from forces, such as hydrodynamic, other than those colloid forces produced by the interaction of the stabiliser barriers of neighbouring particles of the dispersion.

Viscoelasticity-concentration relationships for non-aqueous concentrated dispersions

The effect of added polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) on a dispersion of polystyrene particles stabilised with grafted methoxy PEG chains is discussed. PVA adsorbed more strongly on the particles compared to PVP. Polymer addition led to stable mixtures in the case of PVA compared to depletion phase separation observed in the case of PVP. Rheological measurements showed thickening of the dispersion and absence of any structure in the case of PVA, in contrast to structure formation in the case of PVP due to depletion phase separation. A weak gel state was reached for ca. 7% w/w PVP. The observed behaviour is in accord with the relative propensity of PVA and PVP to interact with the particle surface, the grafted chains and their solubility in water. The solvency of the free polymer chains dominated the overall behaviour while the contribution from the incompatibility between free and grafted chains was conterbalanced by differences in the free polymer adsorption on the particles.

T. A. Strivens

Papers

The viscoelastic properties of concentrated suspensions

The rheological properties of concentrated cetyltrimethylammonium bromide-salicylic acid solutions in water

Viscoelasticity-concentration relationships for non-aqueous concentrated dispersions

Polymer modified colloidal dispersions