Chain Length Dependencies of the Bending Modulus of Surfactant Monolayers

Abstract

The effect of the surfactant chain length n on the bending modulus of surfactant monolayers is simulated with a mesoscopic oil-water-surfactant model. We confirm a power law, / n p , as predicted by mean-field theory and found experimentally, and find p 1:5 at a constant surface density and p 1:0 at a constant interfacial tension. This agrees quite well with both mean-field theory (p 2-3, assuming constant surface density) and experiments (at constant surface tension). Our results suggest that the previously reported agreement between theory and experiment may be fortuitous and caused by the difference in surfactant types.

Sign Switch of Gaussian Bending Modulus for Microemulsions: A Self-Consistent Field Analysis Exploring Scale Invariant Curvature Energies

“…A preeminent challenge is to predict, from a molecular model for such interfaces, a means to induce a sign change in thē κ from negative to positive; this signals the loss of stability of the lamellar, L α , oil-surfactant-water ordering in favor of a phase with saddles, L 3 or sponge-like. Another long-standing problem is understanding the relation between surfactant chain architecture and corresponding bending rigidities [11,12].Earlier theoretical methods [13,14], experiments [15][16][17], and simulations [18,19] that attempted to link bending rigidities to molecular properties did not provide information onκ; moreover, the results for κ were not consistent with each other. Therefore uncertainties prevail and these persist also because internal checks for presented rigidities are rarely provided.…”

“…We focus on the role of the interaction parameter which in strong segregation has a large value and for weak segregation a small value; further, we elaborate on the role of the molecular weights of the solvents and that of the amphiphile. Experiments, simulations, and calculations [13][14][15][16][17][18][19] reviewed above have major disadvantages and ambiguities because the systems featured too many complications. We examine a tensionless balanced interface which still is highly relevant to middle-phase microemulsion systems wherein oil and water are separated by a surfactant film with extensive areas and often a complex interface topology.…”

Mesoscopic models of biological membranes

“…Concerning the nonbonded interactions, they can be represented by Lennard-Jones like potentials, of by soft-repulsive potentials. These lipid models have many points in common with the earlier models developed to study the self-assembly of micelles and surfactant monolayers [69][70][71][72][73]. It is worth mentioning that, despite their simplicity, these models show a remarkable ability to reproduce the structural, thermodynamic and mechanical properties of lipid aggregates (e.g., bilayers and vesicles).…”

Dissipative Particle Dynamics

“…The effect of surfactant chain length on the bending modulus of surfactant monolayer was investigated. 107 In water-in-oil and oil-in-water emulsions, which are thermodynamically unstable, surfactant molecules can slow down or prevent the droplet coalescence process making emulsions kinetically stable. Rupture of the film separating two droplets and their coalescence in oil/water/surfactant systems have been studied.…”