Colloidal Stability Influenced by Inhomogeneous Surfactant Assemblies in Confined Spaces

Abstract

Recently, a molecular-level self-consistent field approach was used to show that some surfactants assemblies (with local cylindrical structure) can bridge between two surfaces that in turn are covered by surfactant bilayers. The stability of such a connection is related to a higher end-cap (free) energy of the worm-like micelle (in solution) than the connection (free) energy of the micelle with the surface layer. This preliminary study has been extended here to know the viability of this connection as a function of different parameters related to the surfactant structure and the interaction between the surfaces and the different moieties composing the surfactant. The effect of such parameters on the structure of the connection, the thermodynamic stability of such a formation, and the interaction curve between such surfaces has been analyzed in case the connection was possible. A secondary minimum has been found, which could give rise to surfactant-induced flocculation. This minimum is strongly affected by the surfactant properties. Other interesting surfactant structures have been predicted to form in confined spaces under certain parameter regimes.

Bilayers Connected by Threadlike Micelles in Amphiphilic Mixtures: A Self-Consistent Field Theory Study

“…Note also the negative curvature of the surface in the regions where the thread joins the bilayers. Junctions of this form have also been seen in lattice SCFT calculations by Jódar-Reyes and Leermakers [35,36] on the closely-related problem of cylindrical micelles bridging two fixed hydrophilic surfaces.…”

“…Note also the negative curvature of the surface in the regions where the thread joins the bilayers. Junctions of this form have also been seen in lattice SCFT calculations by Jódar-Reyes and Leermakers , on the closely related problem of cylindrical micelles bridging two fixed hydrophilic surfaces and in membrane elasticity calculations by May on bilayer fusion . Planar analogues of these junctions can also be found in copolymer/homopolymer blends …”

Directed Self-Assembly of Spheres into a Two-Dimensional Colloidal Crystal by Viscoelastic Stresses

“…In addition, the formation of patches may be determined by the concurrent action of both a first (positive) and a second (negative) normal stress difference, giving rise to a sort of biaxial flow. In fact, nonnegligible N 2 values have been measured in wormlike micellar solutions. , As a final note, it should be remarked that wormlike micelles may alter the colloidal interaction forces and whereas these attractive force are expected to be isotropic in nature and do not lead to the formation of sheets they may help to stabilize the structures.…”

“…In fact, nonnegligible N 2 values have been measured in wormlike micellar solutions. 22,23 As a final note, it should be remarked that wormlike micelles may alter the colloidal interaction forces 24 and whereas these attractive force are expected to be isotropic in nature and do not lead to the formation of sheets they may help to stabilize the structures. Several methods have been presented for the assembly of spheres in 2D sheets, for example, using specific chemistries with directional colloidal interactions, templating, or using capillary interactions between particles at interfaces.…”