Dispersing Multi-Component and Unstable Powders in Aqueous Media Using Comb-Type Anionic Polymers*

Abstract

We have investigated the effect of polymeric dispersants on the rheological properties and consolidation behavior of concentrated cemented carbide (WC-Co) and magnesia (MgO) suspensions. The relatively novel types of comb-type anionic polymers with grafted non-ionic side chains are effective dispersants also in multi-component powder mixtures with a complex solution and surface chemistry and result in more robust suspensions at significantly higher solids loading compared with e.g., a traditional cationic polyelectrolyte. Direct force measurements on comb-type dispersants with different lengths of the grafted ethylene oxide side chains showed that the dispersants adsorb onto a MgO surface and infer a repulsion where the range scales with the length of the poly ethylene oxide side chains. The compressibility and the consolidation behavior of MgO particle networks in response to a centrifugal force field could be related to the estimated thickness of the adsorbed comb-type dispersants.

Dispersion of alumina suspension using comb-like and diblock copolymers produced by RAFT polymerization of AMPS and MPEG

“…These side chains, which are less sensitive to ionic strength, will provide a short-range repulsive steric barrier that is able to counter van der Waals forces when the double layer is highly compressed. Direct evidence of the steric contribution of the PEO segment in comb-like acrylic acid backbone grafted with PEO chains has been produced by Palmqvist et al [20] and by Laarz et al [19] by means of AFM measurement. Given the fact that the DLS technique provides dimensions corresponding to an equivalent sphere size including both the electrostatic double layer and the adsorbed polymer, a rough estimation of the thickness of the adsorbed layer in the case of AMPS-MPEG copolymer may be obtained by subtracting the equivalent sphere hydrodynamic radius from that obtained with AMPS-100, which is known to adopt a flat conformation on alumina particles.…”

“…They showed that above pH 6, acrylic acid groups ensure a strong anchoring effect on oppositely charged oxide surfaces, whereby the neutral PEO teeth extend away from the particle surface and regulate the adsorbed layer density and thickness. More recently, Laarz et al [19] investigated the effect of comb-like polymeric dispersants on the rheological properties and consolidation behavior of concentrated cemented carbide (WC-Co) and magnesia (MgO) suspensions. They showed the possibility of tailoring the repulsive range of the comb-type copolymers by controlling the molecular weight of the grafted PEO-side chains.…”

“…These limitations can be reduced by the recourse to copolymers issued from the polymerization of at least two monomers, one of which has an ionic or ionizable group that impart adsorption and the other is a nonionic structures, such as polyethylene glycol or polypropylene glycol, dangling freely in the solvent which makes steric stabilization possible through an expanded configuration. The use of copolymers, namely those with a comb-like architecture for aqueous processing of colloidal dispersion has not yet been fully explored, and only few studies have been reported [9,10,[17][18][19][20][21].…”

Fluidizing efficiency of comb-like superplasticizers: The effect of the anionic function, the side chain length and the grafting degree

“…the slope of the fluidity/adsorption relationship, results from a combination between backbone charge density and the adsorbed layer thickness. The increase of the side chain density or length leads to thicken or densify the adsorbed layer rising the repulsive steric forces as shown by AFM studies [11,12] or theoretical calculations [13]. Theoretical models which are validated by experimental data can help to tackle the rheology of cement paste such as the conformation model for PCE [12] or the model for predicting the yield stress of a suspension called Yodel [14,15].…”

Effect of molecular weight of an anionic dispersant on the properties of BaTi4O9 slurries

“…Besides, the volume of the final sediment layer was less than that of the BT 4 suspension without the presence of any polymer, as an indication of denser packing of particles. 21,27 If more than 0.5 wt % PAC1 was added, the resulting suspensions became more stabilized and remained cloudy even settled after 30 days. Similar sedimentation behaviors were observed for the BT 4 suspensions with other three PACs, as are shown in Figures 3-5.…”