Effect of Water and Salt on the Colloidal Stability of Latex Particles in Ionic Liquid Solutions

Abstract

The colloidal stability of sulfate (SL) and polyimidazolium-modified sulfate (SL-IP-2) latex particles was studied in an ionic liquid (IL) of ethylammonium nitrate (EAN) and its water mixtures. Aggregation rates were found to vary systematically as a function of the IL-to-water ratio. Repulsive electrostatic interactions between particles dominated at low IL concentrations, while they were significantly screened at intermediate IL concentrations, leading to destabilization of the dispersions. When the IL concentration was further increased, the aggregation of latex particles slowed down due to the increased viscosity and finally, a striking stabilization was observed in the IL-rich regime close to the pure IL solvent. The latter stabilization is due to the formation of IL layers at the interface between particles and IL, which induce repulsive oscillatory forces. The presence of the added salt in the system affected differently the structure of the interfaces around SL and SL-IP-2 particles. The sign of the charge and the composition of the particle surfaces were found to be the most important parameters affecting the colloidal stability. The nature of the counterions also plays an important role in the interfacial properties due to their influence on the structure of the IL surface layers. No evidence was observed for the presence of long-range electrostatic interactions between the particles in pure ILs. The results indicate that the presence of even low concentrations of water and salt in the system (as undesirable impurities) can strongly alter the interfacial structure and thus, the aggregation mechanism in particle IL dispersions.

Structure–Stability Relationship in Aqueous Colloids of Latex Particles and Gemini Surfactants

“…However, 8-4-8, 12-4-12, and 12-6-12 GSs show more complicated behavior, featuring the characteristic U-shaped stability plot, which has been reported for several particle systems containing oppositely charged polyelectrolytes or surfactants. 15 , 16 , 40 , 48 , 49 The SL dispersions were stable at low surfactant concentrations, as indicated by the fairly high stability ratio values determined in this regime. Then, with increasing surfactant amount, the stability ratios decreased and reached a minimum, followed by an increase at higher concentrations, where stable samples were observed.…”

“…A second-order cumulant fit was applied to the correlation function to determine the hydrodynamic radius (R h ). 38 For the early stages of aggregation, the absolute aggregation rate constant (k) was calculated from the initial change of the R h as a function of time (t) as follows 39,40…”

“…A second-order cumulant fit was applied to the correlation function to determine the hydrodynamic radius ( R h ) . For the early stages of aggregation, the absolute aggregation rate constant ( k ) was calculated from the initial change of the R h as a function of time ( t ) as follows , 1 R normalh , 0 true( normald R normalh normald t true) t → 0 = k N 0 ( 1 − R h , 1 R h , 2 ) I 2 ( q ) 2 I 1 ( q ) where R h,0 is the initial hydrodynamic radius, N 0 is the initial number concentration of the particles, and R h,1 and R h,2 correspond to the hydrodynamic radius of the monomer and dimer, respectively. The contribution of the form factors of the monomer ( I 1 ) and dimer ( I 2 ) to the scattered intensity was calculated with the theory developed by Rayleigh, Debye, and Ganswhile .…”

The Influence of Solvents and Colloidal Particles on the Efficiency of Molecular Antioxidants

“…Comparing the charge and aggregation tendencies by altering the SL-to-IP-2 ratio in the samples, it can be stated that the dispersions are unstable near the IEP, while sufficiently charged particles below and above the IEP are more stable. These results imply that the IP-2 dose-dependent colloidal stability of SL can be interpreted with the classical DLVO (Derjaguin, Landau, Verwey and Overbeek) theory [54][55][56][57], which predicts that the overall interparticle forces are determined by the sum of repulsive electrical double layer and attractive van der Waals forces. Indeed, rapid aggregation is observed in the present system near the IEP, under which conditions the van der Waals attractive forces predominate over the weak or even vanished repulsive forces otherwise originating from the overlapping electrical double layers.…”

Colloidal Interactions in Ionic Liquids– the electrical double layer inferred from ion layering and aggregation

“…These studies have shown that the mechanisms underlying particle stability and aggregation are very different in diluted and concentrated ILs. [82][83][84][85] Indeed, the DLVO theory describes well the behavior of particle dispersions in diluted ILs, and hence, electrostatic interactions mainly determine particle stability in this regime. 85 In contrast, viscous and solvation forces explain particle stability in concentrated and pure ILs, and no evidence was found for the action of a long-range electrostatic repulsion between the particles.…”