Self-assembly of ionic surfactants and formation of mesostructures

Abstract

Self-assembly of ionic surfactants resulting in micelle formation is studied using off-lattice Monte Carlo simulation in two dimensions (2D). We find that in addition to the Lennard-Jones (LJ) interaction, which acts among all of the particles, a screened Coulomb interaction, acting only among the surfactant heads, makes the geometric arrangement of micelles very different compared to that for neutral surfactants at the same density. At low concentrations, ionic surfactants produce spherical micelles and exhibit intermicellar ordering arising out of the longer-range repulsion of the surfactant head groups. For larger concentrations, they tend to form bi-layers. Motivated by recent experiments on preparation of mesoporous sieves through surfactant-templating routes, we then extend these studies to micellization of ionic surfactants in the presence of other neutral host particles. The morphologies of the surfactant-host composites are studied as functions of host particle densities, sizes, and their interaction strengths. Assuming the presence of micelles as quenched disorder, we obtain a qualitative understanding of the local ordering of the host particles in terms of a dimensionless density parameter from the known liquid-vapour phase diagram in 2D of a LJ fluid.

Amphiphilic aggregation in hydrogen bonding liquids: Dynamic and equilibrium properties

“…All the CMC curves increase monotonically with temperature, which is expected for non-associating solvent solutions, and for some types of amphiphiles in water. This was also shown to be a general trend for amphiphilic lattice models where solvent molecules have no structure [28]. Although our solvent molecules have internal degrees of freedom, no minimum in CMC (which is seen for SDS surfactants in water) was observed, in accordance with the results for apolar solutes in the square water [17], where the solubility always increases with temperature.…”

Water confined in self-assembled ionic surfactant nano-structures

“…Very limited attention is normally devoted to the features of the adsorbed fluid. Furthermore, most part of the existing numerical investigations are somehow exceedingly focused on the chemical details of the materials or, in contrast, they miss important details in the description of the solvent [34][35][36][37] , relying on heavily coarse-grained models. Obviously, increasing spatial resolution to the atomic level for the surfactant molecules would necessitate unreasonably extended computing resources.On the other hand, neglecting some details of the water molecule has an important influence on the dynamics of the simulated systems, and hampers the possibility of following the evolution of important degrees of freedom.…”

Electrostatic Screening and Charge Correlation Effects in Micellization of Ionic Surfactants

“…42 In many implicit-solvent models of amphiphilic molecules, electrostatic interactions between charged species have been treated with a Debye-Hückel or Yukawa potential that accounts for Coulomb screening. [43][44][45][46][47][48][49] This approach reduces the computational cost, allowing large-scale investigations of structural properties. Similar methods have also been used in protein simulations.…”