Modeling Gas–Liquid Interfaces by Dissipative Particle Dynamics: Adsorption and Surface Tension of Cetyl Trimethyl Ammonium Bromide at the Air–Water Interface

Abstract

Adsorption of surfactants at gas–liquid interfaces that causes reduction in the surface tension is a classical problem in colloid and interface science with multiple practical applications in oil and gas recovery, separations, cosmetics, personal care, and biomedicine. Here, we develop an original coarse-grained model of the liquid–gas interface within the conventional dissipative particle dynamics (DPD) framework with the goal of quantitatively predicting the surface tension in the presence of surfactants. As a practical case-study example, we explore the adsorption of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) on the air–water interface. The gas phase is modeled as a DPD fluid composed of fictitious hard-core “gas” beads with exponentially decaying repulsive potentials to prevent penetration of the liquid phase components. A rigorous parametrization scheme is proposed based on matching the bulk and interfacial properties of water and octane taken as the reference compounds. Quantitative agreement between the simulated and experimental surface tension of CTAB solutions is found for a wide range of bulk surfactant concentrations (∼10–3 to ∼1 mmol/L) with the reduction of the surface tension from ∼72 mN/m (pure water) to the limiting value of ∼37.5 mN/m at the critical micelle concentration. The gas phase DPD model with the proposed parametrization scheme can be extended and applied to modeling various gas–liquid interfaces with surfactant and lipid monolayers, such as bubble suspensions, foams, froths, etc.

Tuning Cationic Micelle Properties with an Antioxidant Additive: A Molecular Perspective

“…Cationic surfactants exhibit a wide range of self-assembled geometries ranging from spherical micelles to short rods (ellipsoidal) or long cylinders to entangled worm-like micelles, vesicles, and liquid crystalline edifices, giving an account of their concentration in aqueous solution. − Studies have reported that these nanoscale morphologies can be fine-tuned by altering the solution environment in the presence of various organic/inorganic additives (anionic hydrotropes, short chain surfactants, salts, etc.) manipulating the temperature, pH, ionic strength, etc. − Such alteration in micellar characteristics impart them the ability to serve as smart materials with excellent potential for rheology control, enhanced oil recovery, delivery of hydrophobic bioactive molecules, etc. − However, to achieve microstructures of higher order, such as worm-like micelles, vesicles, or liquid crystals, the appropriate selection of additives is very crucial.…”

Mesoscale Modeling of Agglomeration of Molecular Bottlebrushes: Focus on Conformations and Clustering Criteria

“…We use the dissipative particle dynamics (DPD) approach [72][73][74][75] to model the time evolution and self-assembly in bottlebrush-solvent systems. DPD is a computationally efficient mesoscale approach that has been utilized to model a broad variety of polymer systems [76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94], including studies of the effects of solvent quality on structural characteristics [95][96][97][98] and self-assembly in various polymer systems [23,79,89]. Herein, we briefly introduce the DPD approach, the details of this approach can be found in [72][73][74].…”

DPD Simulation on the Transformation and Stability of O/W and W/O Microemulsions

“…The lateral force was given by P L (Z) = 1/2[P xx (Z) + P yy (Z)] with the pressure tensor component in the Z direction. The reality units could be transformed from the mean surface tension satisfied using the simulations by γ = γ sim × k B T/R c 2 , with R c = 0.711 nm and T = 298 K [39].…”

“…Th lateral force was given by PL(Z) = 1/2[Pxx(Z) + Pyy(Z)] with the pressure tensor componen in the Z direction. The reality units could be transformed from the mean surface tensio satisfied using the simulations by γ = γsim × kBT/Rc 2 , with Rc = 0.711 nm and T = 298 K [39] As the same content of oil and water as the oil/water = 1/1, surfactants adsorb at a fla interface and form a layer-like aggregate. The highest mean interfacial tension and end t end distance of H1T1 indicate that the surfactant molecular chain is most extended an has the weakest surfactant activity and emulsification capacity.…”

“…Ma et al adopted the molecular dynamic simulation to reveal the molecular mechanisms on the stability and instability of the interfacially active asphaltenes (IAA) stabilized O/W emulsions [30]. Dissipative particle dynamics (DPD) is frequently adopted for liquid systems and can reflect the dynamics on the mesoscopic molecular level of complex fluid systems, as one method of molecular dynamics simulation [35][36][37][38][39]. Furthermore, DPD can provide both the equilibrium thermodynamic properties and the dynamic details and the structural changes over time, which are either difficult or impossible to obtain by measurements [40][41][42].…”