Aggregation of Halloysite Nanotubes in the Presence of Multivalent Ions and Ionic Liquids

Abstract

Colloidal stability was investigated in two types of particle systems, namely, with bare (h-HNT) and polyimidazoliumfunctionalized (h-HNT−IP-2) alkali-treated halloysite nanotubes in solutions of metal salts and ionic liquids (ILs). The valence of the metal ions and the number of carbon atoms in the hydrocarbon chain of the IL cations (1-methylimidazolium (MIM + ), 1-ethyl-3methylimidazolium (EMIM + ), 1-butyl-3-methylimidazolium (BMIM + ), and 1-hexyl-3-methylimidazolium (HMIM + )) were altered in the measurements. For the bare h-HNT with a negative surface charge, multivalent counterions destabilized the dispersions at low values of critical coagulation concentration (CCC) in line with the Schulze−Hardy rule. In the presence of ILs, significant adsorption of HMIM + took place on the h-HNT surface, leading to charge neutralization and overcharging at appropriate concentrations. A weaker affinity was observed for MIM + , EMIM + , and BMIM + , while they adsorbed on the particles to different extents. The order HMIM + < BMIM + < EMIM + < MIM + was obtained for the CCCs of h-HNT, indicating that HMIM + was the most effective in the destabilization of the colloids. For h-HNT−IP-2 with a positive surface charge, no specific interaction was observed between the salt and the IL constituent cations and the particles, i.e., the determined charge and aggregation parameters were the same within experimental error, irrespective of the type of co-ions. These results clearly indicate the relevance of ion adsorption in the colloidal stability of the nanotubes and thus provide useful information for further design of processable h-HNT dispersions.

Cation-induced morphological transitions and aggregation of thermoresponsive PNIPAM nanogels

“…6 (a) and (b). Such flip in the zeta potential was also seen in nanoparticles since higher valency of cations can easily cross the electrical double layer and bind to surface of sample [ 49 , 50 ].

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AFM Characterization of Halloysite Clay Nanocomposites’ Superficial Properties: Current State-of-the-Art and Perspectives

“…In addition, it is possible to have different charges inside and outside the HNTs in a high pH range (i.e., between 3 and 8); in particular, the external surface is negatively charged while the interior has a positive charge [ 20 ] influencing their dispersion in aqueous solution and concentration, as well as on the presence of electrolytes. Besides the pH and charges, the electrolyte presence as well as the concentration is responsible for HNT dispersion [ 21 ]. In addition to these properties, the nanotubes have a cavity very suitable for the confinement of specific molecules, as it represents about 10% of its volume [ 22 ].…”

Colloidal and Thermal Stability of Three‐Component Hybrid Materials Containing Clay Mineral, Polysaccharide and Surfactant

“…[22,23] In order to maintain stability of a colloidal system, the repulsion forces have to be stronger than the attraction ones. [24,25] The gravitational stability refers to the ability of particles to resist particle migration (e. g. sedimentation or creaming). [26] This process depends mainly on the physicochemical and rheological properties of the system.…”

“…The main of them are: Van der Waals attraction, and electrostatic interactions, steric interactions and hydrophobic effect [22,23] . In order to maintain stability of a colloidal system, the repulsion forces have to be stronger than the attraction ones [24,25] . The gravitational stability refers to the ability of particles to resist particle migration (e. g. sedimentation or creaming) [26] .…”