The Electroviscous Behavior of Aqueous Dispersions of Amorphous Silica (Ludox)

The electroviscous effects in very dilute aqueous dispersions of amorphous silica (Ludox) were investigated at various levels of salt, pH, and volume fraction

Response to Comments by M. Kosmulski on “The Electroviscous Behavior of Dispersions of Amorphous Silica (Ludox) in KCl Solutions” by J. Laven and H. N. Stein

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Equilibrium phase diagram of suspensions of electrically stabilized colloidal particles

\u3cp\u3eA second-order perturbation theory based on statistical thermodynamics is employed to calculate the phase diagram of suspensions of charge-stabilized, monodisperse, spherical, colloidal particles that are assumed to interact by a standard DLVO potential. Taking into account van der Waals forces, the phase diagram consists of an ordered colloidal crystal, a disordered fluid phase, and a liquid phase that is formed by particles flocculated into the secondary minimum.\u3c/p\u3

Silver nanoparticles prepared by using poly(2-acrylamido-2-methylpropane sulphonic acid) as a surfactant

Silver nanoparticles were synthesised successfully using poly(2-acrylamido-2-methylpropane sulphonic acid) (PAMPS) as a surfactant. Silver nanoparticles prepared through this approach possess high purity and narrow size distribution. The size distribution result shows that the diameters ranging from 78.82 to 105.709 nm can account for 76.41% of nanoparticles. UV–vis spectra were used to record the formation of silver nanoparticles in detail. It is found that PAMPS can play an important role in the formation and the colloidal stabilisation of silver nanoparticles because of the high affinity of sulphonic and amide with silver ions. The formation is summarised in detail. In addition, a potential application in nanocomposites of this method is explored. The Ag/polyaniline (PANI) nanocomposite prepared using this method shows higher electrical conductivity than that prepared using other methods. This method is novel, convenient, efficient and environmental-friendly, especially suiting those wastewaters treatment facilities containing silver ions. At the same time, it is also promising to prepare Ag/PANI or other metals/polymer composites via in-situ polymerisation

The impact of non-DLVO forces on the onset of shear thickening of concentrated electrically stabilized suspensions

This paper exposes an extension of an activation model previously published by the authors. When particles arranged along the compression axis of a sheared suspension, they may overcome the electrostatic repulsion and form force chains associated with shear thickening. A percolation-based consideration allows an estimation of the impact of the force chains on a flowing suspension. It suggests that similar to mode coupling models, the suspension becomes unstable before the critical stress evaluated from the activation model is reached. The percolated force chains lead to discontinuous shear thickening. The model predictions are compared with results from two experimental studies on aqueous suspensions of inorganic oxides; in one of them, hydration repulsion and in the other hydrophobic attraction can be expected. It is shown that the incorporation of non-Derjaguin-Landau-Verwey-Overbeek forces greatly improve predictions of the shear thickening instability. © Springer-Verlag 2009

Diblock copolymer dispersants in polyester powder coatings

Poly(2-vinylpyridine)-b-poly( -caprolactone) copolymers have been used as dispersants for TiO2 pigments in a polyester/TGIC powder coating. In coatings without TGIC, the block copolymer dispersants prevented the flocculation of the TiO2 pigments at typical curing temperatures, by the formation of a steric barrier around the pigment particles. Consequently, non-crosslinked powder coatings with high gloss and excellent flow were obtained. In the presence of TGIC, the dispersants were found to catalyse the crosslinking reaction, leading to powder coatings with lower gloss and poor levelling. By replacing the basic poly(2-vinylpyridine) anchor block of the dispersants with an acidic or neutral anchor group, this undesired effect may be avoided. Alternatively, the poly(2-vinylpyridine)-b-poly( -caprolactone) dispersants are expected to be of special benefit in powder coatings with alternative crosslinking mechanisms, such as UV curable powder coatings