Viscoelastic Properties of Particle Gels (original) (raw)
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Viscoelasticity of coagulated alumina suspensions
Korea-Australia Rheology Journal, 2012
The solid-to-liquid transition of a model coagulated alumina suspension at concentrations above the gel point was investigated to explore the critical parameter for describing network failure under shear forces. Static (creep and creep-recovery) and dynamic (small and large amplitude oscillatory) shear experiments were combined to examine shear softening in these systems and time-based dependence in the yielding dynamics. The particulate network structure exhibits failure and viscous dissipation under creep and oscillatory shear tests at stress values well below the conventionally defined yield stress. Results from strain recovery tests highlight a time-dependence for failure, where only partial recovery of strain energy was possible once a specific duration of creep was surpassed. The system was observed to fail at a common strain value across all methods of rheology testing. These results are self-consistent, showing a clear transition from the linear to non-linear viscoelastic region for a coagulated material under shear stress. It provides the starting point to incorporate mechanical viscoelastic models to extract time constants for yielding behaviour. This work also presents one of the first reported LAOS and creep results for particulate suspensions using a vane geometry.
Mechanics and Microstructures of Concentrated Particle Gels
Journal of the American Ceramic Society, 2005
It is often assumed that the viscoelastic properties of dense colloids are determined by the colloid volume fraction, the interaction potential, as well as the particle size distribution and shape. The dependence of the viscoelastic behavior of particle suspensions and gels on these parameters has been widely studied, and is well understood in many cases. In contrast, our knowledge on the influence of microstructure on mechanical and rheological properties, in particular for high solid loading suspensions as used in ceramic processing, is much less developed. This aspect has been the focus of recent experiments, which show that small changes in microstructure can have dramatic effects on the mechanics and dynamics of concentrated colloidal gels. In this article, we attempt to give an overview of the influence of microstructure on the mechanical and rheological properties of colloidal systems. Particular attention is given to colloidal particle gels at high volume fractions.
The rheology of deformable and thermoresponsive microgel particles
Polymer, 1995
This paper describes the preparation and characterization of two monodisperse, hydrophilic polymer latices, with different particle diameters, of poly-N-isopropylacrylarnide crosslinked with N, N'methylenebisacrylamide. The uncrosslinked polymer is water soluble and non-ionic and exhibits a lower consolute solution temperature of about 31-32°C. The latex was prepared via a surfactant-free dispersion polymerization route using water as a solvent at a polymerization temperature of 70°C. The physical properties of the resulting latex were strongly dependent on temperature. At high temperatures (65"Q the particle diameters were 23 and 50nm, whilst at 25°C they were 130 and 470 nm. This five-to tenfold increase in the particle diameter corresponds to a lOO-to lOOO-fold increase in volume. Consequently, the rheological properties, both continuous and oscillatory shear, of these systems are strongly dependent on temperature. Volumetric and particle size changes observed by photon correlation spectroscopy and differential scanning calorimetry thermal analysis were in agreement, confirming that the volume phase transition is controlled and influenced by the same factors observed in the swelling/deswelling behaviour of microgels. The viscoelastic properties of these systems and the elasticity of the dispersion decreased as the temperature was increased and the fluid changed from a predominantly elastic to a viscous material. In addition, at lower temperatures, all the studies showed an increase in the storage modulus of the dispersion with increasing particle concentrations. The rheology of the dispersions as a function of the volume fraction of the particles was monitored and the viscosity and shear-thinning increased as volume fraction increased.
Rheology of Concentrated Suspensions Containing Weakly Attractive Alumina Nanoparticles
Journal of The American Ceramic Society, 2006
The use of nanoparticles for the fabrication of new functional ceramics and composites often requires the preparation of concentrated fluid suspensions. However, suspensions containing nanoparticles are limited in solids content because of the excluded volume formed by the dispersant adlayer around the particles. We investigated the effect of the adlayer thickness on the rheological behavior of suspensions containing model alumina nanoparticles, using dispersant molecules with deliberately tailored chain length. The apparent viscosity and yield stress of the particle suspensions were markedly decreased by increasing the dispersant length, mainly due to a reduction of the attractive forces among particles. Fluid suspensions with solids content up to 35 vol% were prepared in toluene using a dispersant length of 2.5 nm. Our experimental results and viscosity predictions based on a hard sphere model indicate that fluid suspensions with up to 43 vol% of 65 nm alumina particles could be prepared using an optimum dispersant length of about 3.6 nm.
personal publication, 2023
Suspensions of solid particles in fluid media are widely used in various fields of industry, from the food, pharmaceutical sectors, production of paints and coatings and composites used in civil construction and the automotive industry. During the processing and application of this material, knowledge of the rheological behavior is essential to obtain the expected result. In the present work, the real possibility of a suspension having simultaneous antagonistic rheological behaviors in relation to the time of application of external stress is presented.
Interaction of binders with dispersant stabilised alumina suspensions
Colloids and Surfaces A-physicochemical and Engineering Aspects, 2000
The rheological response of selected aqueous alumina suspensions, stabilised with a polyelectrolyte or with an organic polyvalent salt dispersant, and including poly(vinyl) alcohol (PVA) as a binder, are described in this study. The polymer dispersant was composed of an ammonium salt of poly(methacrylate) and the organic polyvalent compound was a sodium salt of an aromatic sulphate. The results show that the addition of PVA, without any included dispersant does not significantly influence the rheology of the system. However, in the presence of a dispersant the rheology is greatly affected. At a given concentration of the dispersant, the viscosity, storage and loss moduli all increase, as the PVA concentration is increased. Also, for a given concentration of the PVA, it is observed that the viscosity, storage and loss moduli values increase as the concentration of the dispersant is increased. It is argued that at low PVA concentrations, an excess concentration of the unadsorbed dispersant causes flocculation of the particles in the suspension by a reduction of the repulsive electrostatic (double layer) effect. In contrast, at higher concentrations of the PVA the flocculation of the suspension is promoted via a depletion mechanism. : S 0 9 2 7 -7 7 5 7 ( 9 9 ) 0 0 3 7 4 -X
A series of polycarboxylate ether-based copoly-mers that include acrylic acid, 2-acrylamido-2-methylpropane sulfonic acid, and polyethylene glycol-1000 was synthesized, and the performance of these copolymers as rheology modifiers in aqueous alumina suspensions was characterized. We discussed the effect of monomer feed ratio and molecular weight on dispersing ability of these copoly-mers and on extensional behavior of alumina suspensions. Results of zeta potential analysis determined that using the copolymers even at 0.5 wt.% results in all-negative zeta potentials for the entire pH range (2–12). These copolymers immensely affect the extensional rheological behavior of alu-mina suspensions—while 20 vol.% pure alumina suspension showed severe strain hardening behavior, suspensions with 1 wt.% copolymers and 35 vol.% alumina particles displayed no strain hardening. In this series, the copolymer with lowest molecular weight decreased the extensional viscosity of sus-pensions at the rupture of thread with three orders of magnitude as well.
Rheological Evidence of Gel Formation in Dilute Poly(acrylonitrile) Solutions
Macromolecules, 2013
Rheological studies of low concentration (down to 0.1%) poly(acrylonitrile) (PAN)–dimethyl sulfoxide (DMSO) solutions revealed the existence of a rather unusual effect of the gel-like structure formation, while this phenomenon is absent at higher concentrations (17–24 wt %) of PAN in DMSO. The evidence of the gel-like structure consists in the pronounced yielding, which can be detected in the 0.1–5% concentration range and plateau on the frequency dependence of the storage modulus. In addition, rather large particles were found by the dynamic light scattering method. The gel-like structure of dilute PAN solutions is similar to supramolecular gels, while the gelation of water containing systems brings to mind a phase transition. The observed maximal Newtonian viscosity at the low shear stresses for dilute solutions should be treated as an artifact related to the method of measuring, and at long-term loading the plateau is converted to the yield stress. Dilute PAN/DMSO gels are thixotropic. A possibility of bifurcation (due to coexistence of different states) leads to self-oscillations of the stress response in a wide shear rate region. The dynamic viscosity coincides with the shear apparent viscosity for high concentrations but does not in the low concentration range. Such a kind of rheological behavior is not observed if dimethylformamide or aqueous solution of sodium thiocyanate was used instead of DMSO as a PAN solvent. Possible chemical structures responsible for the gel structure formation are discussed.