Ionic Specificity in Rapid Coagulation of Silica Nanoparticles

Abstract

The Smoluchowski theory has been widely accepted as the basic theory to estimate the rapid coagulation rate of colloidal particles in electrolyte solutions. However, because the size and specificity of molecules and ions are not taken into account, the theory is applicable only if the particle size is large enough to neglect the effects caused by the structured layers composed of water molecules, ions, and hydrated ions adsorbed on the colloidal surface. In the present study, the rapid coagulation rates of silica nanoparticles in concentrated chloride and potassium solutions were measured by using a low-angle light-scattering apparatus, and the dependence of the experimental value of rapid coagulation rate, K, on the particle diameter, D, and also on the Gibbs free energy of hydration of ions, ΔG, was investigated extensively. The following were found. (1) When the particle size was small enough, the value of K reduced exponentially not only with the decreasing particle size but also with the increasing value of (-ΔG) of cations (counterions) in the case of chloride solutions and with that of anions (coions) in the case of potassium solutions. (2) Silica nanoparticles of D ≲ 70 nm in 1 M KNO and KSCN solutions did not coagulate at all, although they coagulated at D ≳ 100 nm as in the other potassium solutions. These unexpected phenomena were explained by the proposed mechanisms.

Transport Behaviors of Colloidal Manganese Dioxide in Aqueous Media: Effects of Ionic Specificity of Monovalent Cations

“…Therefore, the different capacities of cations in shielding the electrostatic repulsion might be related to the different hydration abilities of cations. Highly hydrated cations on the left order (e.g., Li + ) were usually surrounded by water molecules in the aqueous medium through a hydrogen-bonding network, thus forming a tight hydration shell around the ions to weaken the interaction of cations with other colloidal MnO 2 , and the hydration shell even generated repulsive forces between colliding particles, , whereas poorly hydrated cations on the right order (e.g., Rb + ) did not tend to bond with water molecules and were exposed to interact with the functional groups of colloidal MnO 2 , thus gaining higher affinity to absorb onto the particle surface and were more efficient in reducing the absolute magnitude of surface potential to accelerate the aggregation of particles . In order to quantitatively understand the effect of ionic specificity on the aggregation of colloidal MnO 2 , a short-ranged hydration repulsive energy was considered to modify the DLVO theory, and the DLVO and MDLVO interaction energy profiles were calculated and are presented in Figure S2.…”

“…Absorbed cations could affect the interaction between colloids and interfaces by altering the surface properties. Both colloids and interfaces would become more hydrophilic when absorbed by strongly hydrated cations (e.g., Li + ) and then attract the surrounding hydrated water molecules to form a thick but soft adsorbed layer, which could act as a lubricant and increase the affinity of colloids toward interfaces, thus promoting the deposition attachment efficiencies. ,, As for poorly hydrated cations (e.g., Rb + ), they would form a thin and firm layer around colloids and interfaces to generate short-range repulsion and prevent the immediate contact of particles with interfaces, thus leading to a lower deposition attachment efficiency . However, the lower magnitude of zeta potentials of both colloids and interfaces in Rb + solution was more beneficial for deposition.…”

Influence of adsorption of ionic liquid constituents on the stability of layered double hydroxide colloids

“…Previous studies [30][31][32][33][34] on other particle-IL systems pointed out that ion specific effects, similar to inorganic electrolytes, [35][36][37] are important in the presence of IL constituents since they govern the adsorption of ions from solutions. Moreover, IL cations and anions can be arranged in sequences based on their adsorption affinity to a given surface.…”

“…45 In addition, surface adsorption of cations followed the above order and results of calculations revealed that the hydration of both the surface and the ions played a major role in the adsorption mechanism. 46 Particle aggregation studies 31,[34][35][36][37]47,48 shed light on the fact that critical coagulation concentration (CCC) data determined with the same particles in different electrolyte solutions can be ordered in the Hofmeister series too. However, the DLVO (Derjaguin, Landau, Vewey and Overbeek) theory, 49 which describes the surface forces in the presence of salt constituents, failed to predict the dependence of such forces on the type of salts present and consequently, the trends in CCC values measured in various salt solutions.…”

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

“…Hence, the ions of higher valences are more effective in destabilization of the colloidal dispersions. In this way, numerous studies have been published with systems containing nanoparticles and electrolytes of different valences and compositions, in which the aggregation mechanism and predominating interparticle forces were identified; − nevertheless, very limited information is available in the literature for HNT materials in this respect. , …”