Effect of Specific Anion on Templated Crystal Nucleation at the Liquid−Liquid Interface

Abstract

In this work, we have investigated the effect of potassium salts of different anions upon the crystal nucleation of K(2)SO(4) as interfacially templated by a surfactant monolayer of 1-octadecylamine (ODA), in an aqueous microdroplet system bounded by a liquid-liquid interface with 1-decanol. The salts used were K(2)HPO(4), KCl, KBr, KI, KNO(3), and KSCN, present at an initial concentration of 10 mM within an aqueous microdroplet containing K(2)SO(4) at an initial concentration of 287 mM. Supersaturation and subsequent crystallization were isothermally induced by droplet dissolution into the dehydrating decanol phase. The K(2)SO(4) solute crystallization behavior was studied by measurement of the calculated concentration of the solute in the microdroplet at the onset of crystallization, i.e., at the first perceptible microscopic appearance of a solid phase, and by crystal habit. Certain salts, e.g., K(2)HPO(4), had almost no influence on the templating ability of ODA, while the ability of ODA to template nucleation and direct the formation of regular crystal habit of K(2)SO(4) became appreciably disrupted in the presence of more chaotropic anions, such as SCN(-) or NO(3)(-). The propensity for anions to disrupt crystal templating was clearly seen to follow a Hofmeister trend. For crystallization events induced in the absence of ODA, however, these added salts had no influence on the outcome of the events. Microdroplets bounded by an ODA monolayer were also found to undergo droplet shrinkage into the surrounding dehydrating phase at a rate which generally depended upon the nature of the anion in the droplet, with chaotropic anions having an apparent effect of promoting shrinkage. Our findings suggest that the packing or ordering of an ODA monolayer at a liquid-liquid interface is strongly influenced by an interaction between anions in the aqueous phase and the surfactant monolayer at the liquid-liquid interface, which is manifested in its effect upon the crystal templating behavior. These intriguing results can have important implications for the understanding of biomineralization processes which occur in heterogeneous environments.

Crystallization in Confinement

“…A simple approach to studying crystallization within individual droplets is offered by a strategy in which a single droplet is created on the tip of a nanopipette within oil. [130,131] The nanopipette can be created using standard procedures and hydrophobized using silanes to prevent wetting of the glass surface by the aqueous solution (Figure 8). K 2 SO 4 was precipitated in the presence of K 2 HPO 4 , KCl, KBr, KI, KNO 3 within droplets bounded by surfactants and immersed in 1-decanol.…”

Influence of Surfactants on Sodium Chloride Crystallization in Confinement

“…This configuration enables them to adsorb at the interface between two immiscible liquids such as oil/water and water/air. Surfactants can also adsorb at solid–liquid interfaces and may even adsorb differently on different crystal facets, which has a significant influence on crystal nucleation and growth. − Most studies report that the presence of surfactants inhibits crystallization, but there are also known exceptions in which to the contrary they increase the nucleation rate. For instance, the presence of sodium dodecyl sulfate was observed to increase the nucleation rate of MgSO 4 .…”

Crystallization of Palladium(II)-Pyridylazophenol Complex at the Liquid-Liquid Interface

“…The formation of crystals, aggregates and precipitates at the liquid-liquid interface in solvent extraction system appeared very often. There have been several reports about the formation of the crystals at the liquidliquid interface [3][4][5][6]. Previously, we reported some aggregate formations at the liquid-liquid interface [7,8].…”