Abstract
We study the lateral capillary interactions between colloids beneath an oil-water interface that lead to closely packed two-dimensional self-assembled colloidal crystals. These capillary forces are caused by the overlap of deformed interfaces above colloids on a solid substrate. The interface deformation is due to the electrostatic disjoining pressure between the charged particles and the charged oil-water interface. It is notable that the short-range (i.e., on the nanometer scale) and out-of-plane electrostatic double-layer interactions, which occur through an aqueous phase, can generate the long-range lateral capillary attraction (i.e., on the micrometer scale).
Highlights
IntroductionThe microstructure and stability of colloidal dispersions are determined by several factors, such as the volume fraction of particles, concentration of additives (i.e., electrolytes, surfactants, and polymers), temperature, and the dielectric constant of the fluid medium.[1,2,3,4,5,6] In particular, when colloids are confined at a two-dimensional (2D) fluid–fluid interface, where one phase is an electrolyte medium and the other carries relatively few charges (i.e., air–water or oil–water interfaces), they interact on a long-range O(1)–O(2) micrometer scale.[7,8,9] This interaction is attributed to two interparticle interaction forces: electrostatic interactions[10,11,12,13,14,15,16] and capillary interactions.[13,17,18,19] By controlling such interaction forces, the colloidal microstructure and mechanical/rheological behaviors can be manipulated.[12,20,21,22,23]
Such electrostatic interactions between dissimilar surfaces, which are typically shortrange, can generate a long-range capillary force that acts as the driving force for the assembly of particles that are captured between the interface and a solid substrate.[32]
It is found that the capillary force decays as Fcap B 1/L, which is a hallmark of capillary forces caused by symmetric and monopolar interface deformation.[17]
Summary
The microstructure and stability of colloidal dispersions are determined by several factors, such as the volume fraction of particles, concentration of additives (i.e., electrolytes, surfactants, and polymers), temperature, and the dielectric constant of the fluid medium.[1,2,3,4,5,6] In particular, when colloids are confined at a two-dimensional (2D) fluid–fluid interface, where one phase is an electrolyte medium and the other carries relatively few charges (i.e., air–water or oil–water interfaces), they interact on a long-range O(1)–O(2) micrometer scale.[7,8,9] This interaction is attributed to two interparticle interaction forces: electrostatic interactions[10,11,12,13,14,15,16] and capillary interactions.[13,17,18,19] By controlling such interaction forces, the colloidal microstructure and mechanical/rheological behaviors can be manipulated.[12,20,21,22,23] Such electrostatic interactions between dissimilar surfaces (i.e., colloidal particles and oil–water interfaces), which are typically shortrange (i.e., nanometer scale), can generate a long-range capillary force that acts as the driving force for the assembly of particles that are captured between the interface and a solid substrate (i.e., the fluid interface templating method).[32] the height of an oil–water interface decreases via hydrostatic pressure. This paper presents a detailed mechanism of this newly discovered type of capillary interaction
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