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Shiv Nadar University

Dissipative particle dynamics (DPD) simulations has been performed to study the phase transition of a mixture of cationic and anionic surfactants in an aqueous solution as a function of the total concentration in water and the relative ratio of surfactants. The impact of the relative difference between the tail lengths of the cationic and anionic surfactants on the phase diagram has been simulated by tuning the number of DPD beads in the simulation model. This research also discusses the impact of the frequently used values of the parameters associated with the harmonic bonds among the bonded DPD beads on the obtained self-Assemblies. We find remarkable differences in the resultant self-Assemblies based on different choices of harmonic bond parameters. The performed simulations show an enhanced spectrum of self-Assemblies with augmented tail lengths and disparate harmonic bond parameters. The obtained self-Assemblies are quite unique and can potentially be used in the future for various applications. We also compare the simulation results of the vesicle structures obtained by modeling the electrostatic interaction in the simulation among the charged beads by explicitly introducing charges with a long-range interaction with those obtained by tuning the implicit electrostatic interaction without the long-range interaction. The effects of the chain length of the model and the harmonic bond parameters on the internal density of DPD beads and stress profiles within the vesicles are examined closely. These results are a significant contribution to understanding the stability of the phases and tailoring of the desired vesicles. © 2022 American Chemical Society. All rights reserved.

World University root node

Physics

(SoNS) School of Natural Sciences

ACS Omega

Phase Diagram Study of Catanionic Surfactants Using Dissipative Particle Dynamics

Dissipative particle dynamics (DPD) simulations are performed to study the phase transition of sodium dodecyl sulfate (SDS) in aqueous solution, which is an anionic surfactant commonly known as sodium dodecyl sulfate. In this work, the aim is to find a coarse-grained minimal model suitable to produce the full phase diagram of SDS. We examine the coarse-grained models of SDS, which have been used in earlier computational studies to produce the phases as well as for finding the critical micelle concentration (CMC) of SDS. We contrast the results based on these models with the experimental observations to assess their accuracy. Our research also takes into account the importance of sodium ions, which come from the partial dissociation of SDS, when dissolved in water. The effect of sodium ion has not been considered explicitly in the computational work done so far using dissipative particle dynamics. In light of the above explorations, we propose new models for SDS and demonstrate that they successfully produce a compendious SDS phase diagram, which can precisely overlay the experimental results. Copyright © 2020 American Chemical Society.

Fulltext

Phase diagram study of sodium dodecyl sulfate using dissipative particle dynamics

In the present study, an ionic liquid (IL), known as green solvent, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4) with four carbons in the hydrophobic chain (C-4) has been used as an additive to modify the self-assembled aggregates of an anionic surfactant sodium dodecyl sulfate (SDS) and then the evolution of the liquid crystalline phases has been investigated. Small angle synchrotron x-ray diffraction study has revealed an unprecedented phase sequence where a hexagonal phase (HI) of direct cylindrical micelles is observed to evolve to another hexagonal phase (HII) of, again, direct cylindrical micelles with a lamellar phase (Lα) as the intermediate. The rheological data and the theoretical calculations have confirmed the phases. To understand such a phase behaviour of the system, the work is extended by considering the ionic liquids with the same head group but of shorter (C-2) and longer (C-10) hydrocarbon chains compared to BMIM-BF4. While the shorter chain IL causes the hexagonal phase to form rectangular (R) phase, the longer chain is observed to induce the lamellar phase (Lα). The molecular mechanism of appearance of such different phases has been discussed. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.

Liquid Crystals

Re-entrant direct hexagonal phases in a lyotropic system of surfactant induced by an ionic liquid

Hamiltonians that are multivalued functions of momenta are of topical interest since they correspond to the Lagrangians containing higher-degree time derivatives. Incidentally, such classes of branched Hamiltonians lead to certain not too well understood ambiguities in the procedure of the quantization. Within this framework we pick up a model which samples the latter ambiguities and which, simultaneously, turns out to be amenable to a transparent analytic and perturbative treatment. © Published under licence by IOP Publishing Ltd.

Journal of Physics: Conference Series

Branched Hamiltonians for a Class of Velocity Dependent Potentials

When a binary liquid is confined by a strongly repulsive wall, the local density is depleted near the wall and an interface similar to that between the liquid and its vapor is formed. This analogy suggests that the composition of the binary liquid near this interface should exhibit spatial modulation similar to that near a liquid-vapor interface even if the interactions of the wall with the two components of the liquid are the same. The Guggenheim adsorption relation quantifies the concentrations of two components of a binary mixture near a liquid-vapor interface and qualitatively states that the majority (minority) component enriches the interface for negative (positive) mixing energy if the surface tensions of the two components are not very different. From molecular dynamics simulations of binary mixtures with different compositions and interactions we find that the Guggenheim relation is qualitatively satisfied at wall-induced interfaces for systems with negative mixing energy at all state points considered. For systems with positive mixing energy, this relation is found to be qualitatively valid at low densities, while it is violated at state points with high density where correlations in the liquid are strong. This observation is validated by a calculation of the density profiles of the two components of the mixture using density functional theory with the Ramakrishnan-Yussouff free-energy functional. Possible reasons for the violation of the Guggenheim relation are discussed. ©2015 American Physical Society.