CHEMICAL ENGINEERING TRANSACTIONS DPD Simulation of Surface Wettability Alteration by Added Water-Soluble Surfactant in the Presence of Indigenous Oil- Soluble Surfactant (original) (raw)

Dpd Simulation of Surface Wettability Alteration by Added Water-soluble Surfactant in the Presence of Indigenous Oil-soluble Surfactant

Chemical engineering transactions, 2017

The effect of a surfactant on wettability alteration and emulsion inversion is studied using Dissipative Particle Dynamics (DPD) modeling. The DPD model contains 1200 oil molecules, 4800 water molecules, 400 oil soluble (indigenous to the oil) surfactants with a head-tail configuration and 400 water soluble molecules to mimic a surface active chemical/ion in the water. Results show that surfactant migrates to the fluid-fluid interface in general, where its potential energy is minimal. However, thermal kinetic energy can lead to a “tunneling” through the interface and into the other phase with a small probability. The same effect lead to migration of the oil soluble surfactant from the oil phase onto the water wet surface, and caused wetting alternation from a water-wet to a surfactant coated effectively oil-wetting surface. The water soluble surface active molecule suppressed this effect when added. Additional emulsion inversion studies confirmed the “Bancroft rule”: oil-in-water em...

Molecular dynamics simulations of model oil/water/surfactant systems

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1994

Molecular dynamics simulations have been performed on amphiphilic molecules, oil and water to investigate surfactant behavior in water-like and oil-like solvents. Using a simple model for water, oil and surfactant molecules on a powerful parallel computer, we were able to simulate the adsorption of surfactants at the water/oil interface and the self-assembly of surfactant molecules into micelles. Simulations on various classes of surfactant molecules with different headgroup sizes and interactions show a strong dependence of the dynamics and morphology of surfactant aggregates on the surfactant structure. In the presence of an oil droplet, micelles induce the transfer of oil molecules from the oil droplet to the micelles by means of three mechanisms.

DPD simulations of surfactants in oil-water systems

2003

In a mixture of oil and water the interfacial tension is reduced by surfactants, amphiphilic molecules. The influence of the structure of these surfactants on the interfacial tension is studied with the Dissipative Particle Dynamics (DPD) technique. It can be concluded that both increasing the length of the hydrophobic tail and hydrophilic head group of a linear surfactant has a positive effect on the decrease of the interfacial tension of an oil–water system. However, the effect of increasing tail length is less pronounced for ...

Analysis of Surfactant and Polymer Behavior on Water/Oil Systems as Additives in Enhanced Oil Recovery (EOR) Technology through Molecular Dynamics Simulation: A Preliminary Study

Journal of Earth Energy Engineering

The decline in oil production has led to the development of the Enhanced Oil Recovery (EOR) technology to increase oil production. Chemical injection is one of the methods in EOR by injecting surfactants or polymers into reservoir wells. To understand the properties and dynamics of surfactants and polymers at the nanoscale, computational studies using molecular dynamics simulation were carried out. In this study, surfactant Sodium Dodecyl Benzene Sulfonate (SDBS) and polymers such as Polyacrylamide (PAM) were used to investigate their effect on the oil-water interface system at the atomic level. Molecular dynamics simulation was carried out using Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) to calculate the diffusion coefficient and Interface Formation Energy (IFE) value for the addition of the surfactant and polymers. The simulation results show that the addition of the surfactant and polymers affects the water-oil interface system differently. The diffusion c...

Molecular modeling of surfactant covered oil-water interfaces: Dynamics, microstructure, and barrier for mass transport

The Journal of Chemical Physics, 2008

Mass transport across surfactant-covered oil-water interfaces of microemulsions plays an important role in numerous applications. In the current work, we use coarse-grained molecular dynamics simulations to investigate model systems containing flat hexadecane-water interfaces covered by monolayers of nonionic surfactants of various lengths. Several properties of the surfactant monolayers relevant to the mass transport are considered, including the monolayer microstructure, dynamics, and a free energy barrier to the solute transport. It is observed that the dominant contribution of a surfactant monolayer to the free energy barrier is a steric repulsion caused by a local density increase inside the monolayer. The local densities, and hence the free energy barriers, are larger for monolayers composed of longer surfactants. Since it is likely that the solute transport mechanism involves a sequence of jumps between short-lived pores within a monolayer, we perform a detailed analysis of s...

Quantifying single oil-particle interactions in aqueous media

Detailed knowledge about the single-pair interactions between a rigid micro-particle and a liquid drop or air bubble immersed in some fluid is one way to predict and/or design the ensemble behavior of mixed colloidal materials, emulsions and other hybrid dispersions, from a kind of first-principles approach. The invention of the atomic force microscope (AFM) has made it possible to accomplish the direct measurement of forces from the interaction of a colloidal particle with a solid object, bubble or droplet. However, there are several fundamental difficulties with a compliant sample that must be addressed before colloidal microscopy can be applied quantitatively to academic studies and practical applications. The purpose of this work is to develop a general method for approaching AFM investigations of highly deformable fluid interfaces and to demonstrate its usefulness in specific areas of interest. These studies are the first to quantify film drainage and rupture times of aqueous films with AFM between a rigid micro-particle (toner) and an oil drop under dynamic conditions similar to paper recycling. It is also shown that electrosteric stabilization of the oil/water interface due to adsorbing cationic polyelectrolytes may be reversed via lipophilic surfactant addition to the oil. Other investigations of more idealized systems show the necessity of detailed AFM experiments to determine unknown interaction parameters for hydrophobically-driven phenomena. The so-called electrolyte titration is developed to control the net attraction between a hydrophobized-silica sphere and plate, revealing a characteristic curve of probe snap-in distance with concentration that allows accurate fitting of multiple surface forces parameters. From this knowledge, a theoretical force analysis of a sphere deforming a curved fluid interface is developed and tested on an oil drop with a polystyrene sphere in water. Fluid interface (FI)-AFM is then adapted to reveal the complexities of the hydrodynamics in a spherically wrapping thin film and of the effects of changing interfacial tension with ionic surfactants.

Molecular Dynamics Study of Nanoparticles and Non-Ionic Surfactant at an OilWater Interface

2020

Nanoparticles (NPs) and surfactants can spontaneously concentrate at the interface between two immiscible liquids, such as oil and water. Systems of high oil-water interfacial area, such as emulsions, are the basis of many industries and consumer products. Although NPs and surfactants are currently incorporated into many of these applications, their mutual interfacial behavior is not completely understood. Here we present molecular dynamics simulations of NPs and non-ionic surfactant in the vicinity of an oil-water interface. It was found that in low concentration the surfactants and NPs show cooperative behavior in lowering the oil-water interfacial tension, while at higher surfactant concentration this synergy is attenuated. It was also found that binding of surfactants to the NP surface decreases the surfactant efficiency in lowering the interfacial tension, while concurrently creating a barrier to NP aggregation.

Dissipative Particle Dynamics (DPD) Study of Crude Oil−Water Emulsions in the Presence of a Functionalized Co-polymer †

Energy & Fuels, 2011

This work presents a theoretical study of the effects of different molecular weights of a triblock co-polymer ethylene oxide/propylene oxide/ethylene oxide, bifunctionalized with ethalamine, on the coalescence of water drops imbibed in a crude oil environment. The polymer/crude oil/water (PCW) time evolution of the emulsion was simulated using the framework of the dissipative particle dynamics (DPD) technique. The bead-bead interactions of the molecular components were calculated using the correlation between the solubility parameter, χ ij , of the Flory-Huggins theory and the conservative force parameter, a ij . The solubility parameter was obtained from atomic molecular models of prototype molecules of saturates, aromatics, resins, asphaltenes, and the triblock co-polymer, through the blend methodology. The dynamic evolution of coarse-grain mesomolecules was carried out in cells of 20 Â 20 Â 20 DPD unit length with periodic boundary conditions. The composition of the emulsion was chosen to be similar to a Mexican heavy crude oil: asphaltenes, 11.9%; resins, 11.8%; aromatics, 42.7%; saturates, 29.6%; polymer, 4%; and two water drops of 3 DPD length units in radius. Finally, a drastic change in the coalescence of water molecules is observed for a short co-polymer length with respect to long co-polymer lengths.

Structure of a water/oil interface in the presence of micelles: a computer simulation study

The Journal of Physical Chemistry, 1991

In this article we present the results of computer simulations on a simple oil/water/surfactant system. These simulations show surprisingly rich structural detail. A monolayer of surfactants is formed at the oil/water interface, and in the water phase spontaneous micellization has occurred. A depletion layer, containing only water, separates the monolayer from the micelles. The density profile of the micelles oscillates close to the interface. It is suggested that these oscillations provide an explanation of the results of neutron reflectivity ...

Molecular Dynamics Simulations of Surfactant Functionalized Nanoparticles in the Vicinity of an Oil/Water Interface

2010

The localization of nanoparticles (NPs) at fluid/fluid interfaces has emerged as an effective self-assembly method. To understand the fundamentals of this localization mechanism, it is necessary to quantify the physical behavior of NPs in the vicinity of a fluid interface. Conventional theories treat the NP as a rigid object whose equilibrium position is dictated by the balance of its surface tensions with the two fluids. However, most NPs are functionalized with “soft ” organic surface layers which play a large role in determining the shape of the NP. Through molecular dynamics simulations, we show that the functionalizing layer also greatly alters the interfacial behavior of the NP beyond the scope of common theory. Furthermore, we characterize the effect of the surface density of functionalizing molecules on the NP deformability. Our results have implications on the experimental interpretation of NP contact angles and may be useful for future theory development.