Dispersant Adsorption and Viscoelasticity of Alumina Suspensions Measured by Quartz Crystal Microbalance with Dissipation Monitoring and in Situ Dynamic Rheology

Abstract

Adsorption behavior and water content of adsorbed layers of four dispersants for aqueous ceramic processing were studied by quartz crystal microbalance with dissipation monitoring (QCM-D) on alumina surfaces. The dispersants were a poly(acrylic acid), a lignosulfonate, and two hydrophilic comb copolymers with nonionic polyoxyethylene chains of different molecular weights. A Voigt model was applied to analyze the viscoelastic behavior of the adsorbed dispersant layers. The results from QCM-D were compared with viscoelastic properties determined by in situ dynamic rheology measurements of highly concentrated alumina suspensions during slip casting. The QCM-D results showed that both the poly(acrylic acid) and the lignosulfonate adsorbed in low amounts and in a flat conformation, which generated thin, highly rigid layers less than 1 nm thick. The water content of these layers was found to be around 30% for the lignosulfonate and 35% for the poly(acrylic acid). High casting rate and strength in terms of storage modulus were observed in the final consolidate of the suspensions with the two polyelectrolytes. In contrast, the high molecular weight comb copolymer adsorbed in a less elastic layer with a thickness of about 6 nm, which is enough to provide steric stabilization. The viscous behavior of this layer was attributed to high water content, which was calculated to be around 90%. Such a water-rich layer gives a lubrication effect, which allows for reorientation of particles during the consolidation process, resulting in a high final strength of the ceramic material. During consolidation, the suspension showed a slow casting rate, most likely due to rearrangement facilitated by the lubricating layer. The short-chain comb copolymer adsorbed in a 1.5 nm thick, rigid layer and gave low final strength to the consolidated suspension. It is likely that the poor consolidation behavior is caused by flocculation due to insufficient stabilization of the dispersion.

Deposition behavior of residual aluminum in drinking water distribution system: Effect of aluminum speciation

“…QCM-D application for adsorption layer characterization has been previously described (Palmqvist and Holmberg, 2008). The general principle is to apply a voltage to the electrodes affixed to the quartz crystal which resulted in oscillations of piezoelectric quartz crystal.…”

Investigation of the adsorption characteristics of natural organic matter from typical Chinese surface waters onto alumina using quartz crystal microbalance with dissipation

“…QCM-D technology has been previously described [16,17,20,21]. A QCM-D E1 system (Q-Sense AB, Gothenburg, Sweden) was used to examine the adsorption of NOM onto Al 2 O 3 surfaces.…”

“…Quartz crystal microbalance with dissipation monitoring (QCM-D) is a useful technique for low-affinity cases, as QCM-D can quantify relatively low levels of adsorbed NOM (ng cm −2 ) in real-time monitoring [16]. Recently, the QCM-D technique was used in environmental studies to detect the adsorption of organic compounds such as dispersants [17,18] and bacterial extracellular polysaccharides to SiO 2 surface [16,19] due to the high sensitivity of this technique.…”

Biomacromoléculas carboximetiladas: atuação como agentes de estabilização de suspensões aquosas de alumina

“…Nessa classe de compostos estão os polieletrólitos, polímeros que possuem grupos com cargas em sua estrutura, ou que podem assumir cargas em solução, podendo contribuir para a estabilidade da suspensão como conseqüência da modificação do perfil elétrico das partículas do sistema, conforme detalhado posteriormente. (Ortega et al, 1997;Raichur, 2007;Holmberg, 2008;Bráulio et al, 2009) …”

“…(Graule;Gauckler, 1993;Holmberg, 2008) A discussão sobre adsorção de polímeros sobre a superfície de óxido em meio aquoso deve levar em conta primeiramente, a interface óxido-líquido. Quando óxidos como Al 2 O 3 , TiO 2 ou Fe 2 O 3 estão imersos em solução aquosa, a superfície tende a coordenar moléculas de água e a dissociação dessas moléculas gera cargas no sistema, que migram para a interface óxido-líquido levando à formação da dupla camada elétrica, (DCE) (Vincent, 1974;Oliveira et al, 2000;Bouhamed et al, 2007) A dupla camada elétrica é de suma importância para se entender a adsorção de polímeros e surfactantes.…”