Jamming rheology of model cementitious suspensions composed of comb‐polymer stabilized magnesium oxide particles

Abstract

The colloidal microstructure of concentrated suspensions containing anionic comb-polymer-stabilized magnesium oxide (MgO) particles in water was analyzed by shear rheometry for indications of changes in particle microstructure based on particle size and comb-polymer usage. As the suspensions were sheared at different rates, jamming in the sheared MgO suspensions was observed as shear stress overshoots. The shear-induced evolution of the suspension's microstructure was strongly related to the perceived interactions between neighboring MgO particles in the suspension. In the jammed state, interactions are believed to be enhanced by the formation of entanglements between opposing comb-polymer side-chains. Steric repulsion between side-chains was lessened for large particles on account of their diameters, which further enabled side-chain entanglement during close particle contact under shear. Suspensions with relatively wide particle size distributions (0.5-400 lm) were theorized to form hydrocluster aggregates, while suspensions with narrower particle size distributions (0.5-40 lm) most likely resulted in networked microstructures under the influence of the chain entanglements from the adsorbed comb-polymer.

Stabilizing Highly Loaded Silicon Nitride Aqueous Suspensions Using Comb Polymer Concrete Superplasticizers

“…This suggests that these larger molecular weight comb polymers could have a greater steric stabilization effect due to their larger size. The magnitude of the molecular weight discovered here is consistent with reports from other research teams that found molecular weights around 20 000 g/mol of a similar concrete superplasticizer . It has been found in a study by Laarz and Bergstrom on stabilizing Si 3 N 4 at lower solids loading (20 vol%) that PMAA‐PEO grafted comb polymers effective as dispersants had molecular weights ranging from 37 200 to 43 200 g/mol …”

Influence of adsorbed and nonadsorbed polymer additives on the viscosity of magnesium oxide suspensions

“…For example, the 30% free PEG suspension had an effective polymer concentration of 5.4 mg/mL surrounding the particles compared to the 18 mg/mL concentration of adsorbed PAA‐PEO comb‐polymer. In a previous study, it was found through ultraviolet–vis spectroscopy that less than 5% of the PAA‐PEO chains do not adsorb to particles …”

“…MgO particles were obtained from Martin Marietta Magnesia Specialties (MagChem P98 pulverized, Martin Marietta Magnesia, Baltimore, MD). Previous characterization of the MgO particles revealed the average particle size to be ∼4 µm with a range of sizes between 0.5 and 40 µm . ADVA 190 (Grace Construction, Cambridge, MA), a commercial water‐reducing PCE used in Portland cements, was applied as an additive for MgO suspensions.…”

“…ADVA 190 (Grace Construction, Cambridge, MA), a commercial water‐reducing PCE used in Portland cements, was applied as an additive for MgO suspensions. Previous work delineated the chemical structure of comb‐polymer, which consists of ∼5000 g/mol poly(acrylic acid) (PAA) and ∼151,000 g/mol grafted poly(ethylene oxide) (PEO) side chains (PAA‐PEO) . PAA‐PEO was dialyzed prior to use in order to remove any low‐molecular weight species .…”

“…Previous work delineated the chemical structure of comb‐polymer, which consists of ∼5000 g/mol poly(acrylic acid) (PAA) and ∼151,000 g/mol grafted poly(ethylene oxide) (PEO) side chains (PAA‐PEO) . PAA‐PEO was dialyzed prior to use in order to remove any low‐molecular weight species . The free, nonadsorbing polymer PEG of molecular weight 1000 g/mol was obtained from Sigma Aldrich and used without further purification.…”