Yield Stress Enhancement of a Ternary Colloidal Suspension via the Addition of Minute Amounts of Sodium Alginate to the Interparticle Capillary Bridges

Abstract

Capillary suspensions are ternary solid–liquid–liquid systems produced via the addition of a small amount of secondary fluid to the bulk fluid that contained the dispersed solid particles. The secondary fluid could exert strong capillary forces between the particles and dramatically change the rheological properties of the suspension. So far, research has focused on capillary suspensions that consist of additive-free fluids, whereas capillary suspensions with additives, particularly those of large molecular weight that are highly relevant for industrial purposes, have been relatively less studied. In this study, we performed a systematic analysis of the properties of capillary suspensions that consist of paraffin oil (bulk phase), water (secondary phase), and α-Al2O3 microparticles (particle phase), in which the aqueous secondary phase contained an important eco-friendly polymeric binder, sodium alginate (SA). It was determined that the yield stress of the suspension increased significantly with the increase in the SA content in the aqueous secondary phase, which was attributed to the synergistic effect of the capillary force and hydrogen bonding force that may be related to the increase in the number of capillary bridges. The amounts of SA used to induce a significant change in the yield stress in this study were very small (<0.02% of the total sample volume). The addition of Ca2+ ions to the SA-containing secondary phase further increased the yield stress with possible gelation of the SA chainsin the presence of excess Ca2+ ions, however, the yield stress decreased because of the microscopic phase separation that occurred in the aqueous secondary phase. The microstructures of the sintered porous materials that were produced by using capillary suspensions as precursors were qualitatively well correlated to the rheological behavior of the precursor suspensions, suggesting a new method for the subtle control of the microstructures of porous materials using the addition of minute amounts of polymeric additives.

Liquid‐Suspended and Liquid‐Bridged Liquid Metal Microdroplets

“…[28,[30][31][32][33][34][35][36][37] To further increase the strength of the EGaIn-in-oil suspension, we employed a polymeric liquid bridge, polyethylene glycol diacrylate (PEGDA) with a number average molar mass (M n ) of 250 Da. PEGDA is in the liquid state at room temperature and has a much higher viscosity (15 cP) than water (1 cP); thus, we anticipated that it would form a stronger capillary bridge [55,58,59] between the EGaIn particles. The primary objective of employing a high-viscosity liquid bridge is to enhance the viscous force contribution, rather than the capillary force contribution, to the total rupture force of the liquid bridge.…”

Direct-Writable and Thermally One-Step Curable “Water-Stained” Epoxy Composite Inks

“…The enhanced rheological strength of the uncured ink might be attributed to the capillary attraction between the dispersed particles, induced by water, as the “secondary” fluid immiscible with the bulk (epoxy resin–hardener) fluid [ 21 , 22 , 23 ]. The three-phase contact angle ( ) of water on the alumina surface in the bulk fluid was determined by measuring the advancing contact angle of a water droplet on a commercial alumina macroplate immersed in an uncured liquid mixture of BADGE and HMPA, and using Wenzel’s equation [ 23 , 24 ]: where θ app is the measured apparent contact angle on the non-ideal surface of an intrinsic (or thermodynamic) contact angle of and a rugosity factor of . The of ~76° inferred by taking known for the alumina macroplate into account, which is close to that of the pelletized surface of alumina microplates used in the current study [ 23 ], suggests that water preferentially wets the alumina surface immersed in the bulk fluid.…”

“…The three-phase contact angle ( ) of water on the alumina surface in the bulk fluid was determined by measuring the advancing contact angle of a water droplet on a commercial alumina macroplate immersed in an uncured liquid mixture of BADGE and HMPA, and using Wenzel’s equation [ 23 , 24 ]: where θ app is the measured apparent contact angle on the non-ideal surface of an intrinsic (or thermodynamic) contact angle of and a rugosity factor of . The of ~76° inferred by taking known for the alumina macroplate into account, which is close to that of the pelletized surface of alumina microplates used in the current study [ 23 ], suggests that water preferentially wets the alumina surface immersed in the bulk fluid. This forms a pendular bridge (θ < 90°), a notion opposite to a capillary bridge (θ > 90°), for which the bulk fluid preferentially wets the surfaces [ 21 ] and thus exerts an attractive capillary force between the bridged alumina particles ( Figure 5 a).…”

“…This forms a pendular bridge (θ < 90°), a notion opposite to a capillary bridge (θ > 90°), for which the bulk fluid preferentially wets the surfaces [ 21 ] and thus exerts an attractive capillary force between the bridged alumina particles ( Figure 5 a). According to the literature [ 22 , 23 ], the of a ternary colloidal suspension consisting of the particles and the bulk and (a small amount of) secondary fluids, often referred to as a “capillary” suspension [ 21 ], may be described as where is the capillary force, γ is the interfacial tension between the bulk and secondary fluids, a is the radius of the particles, is a function of the particle volume fraction ( ) and the number of secondary fluid bridges per unit volume ( ), and is a function of the volume of bridge ( ). While the factors and strongly depend on the system components and processing conditions, and thus have not been described in a closed form yet, γcosθ may be an important parameter that determines the magnitude of the capillary force.…”

“…While the factors and strongly depend on the system components and processing conditions, and thus have not been described in a closed form yet, γcosθ may be an important parameter that determines the magnitude of the capillary force. As a control, it was previously shown that the addition of a small amount of water (2 vol.%) to a colloidal suspension comprising a paraffin oil and exactly the same alumina microparticles (25 vol.%) dramatically increased the suspension strength, achieving a y of ~2000 Pa [ 23 ]. In this pure unreactive nonpolar bulk fluid, the inferred θ was ~46° and the was ~34 mN/m, and thus, the was ~23 mN/m.…”