Simulation of surfactant adsorption at liquid-liquid interface: What we may expect from soft-core models?

The present work attempts to systematically explore the surfactant sorption at liquid-liquid interfaces with coarse-grained models targeting thermodynamic properties of reference liquid solutions. We employ dissipative particle dynamics with soft-core forcefield tested against experimental data on micellization of surfactants in water, and the previous results are reproduced in this work. We consider three different nonionic surfactants: hexaethylene glycol monododecyl ether (CE), 2-[4-(2,4,4-trimethylpentan-2-yl)phenoxy]ethanol) known as Triton X-100 (TX-100), and two alkyl glucoside surfactants (CG) with n-alkane tail fragments and a saccharide hydrophilic head at decane-water and toluene-water interfaces.

Interactions of Crosslinked Polyacrylic Acid Polyelectrolyte Gels with Nonionic and Ionic Surfactants.

The morphology and stability of surfactant-loaded polyelectrolyte gels are of great interest for a variety of personal care, cosmetic, and pharmaceutical products. However, the mechanisms of surfactant interactions with gel-forming polymers are poorly understood and experimentally challenging. The aim of this work is to explore the specifics of surfactant absorption within polyelectrolyte gels drawing on the examples of typical non-ionic octaethylene glycol monooctyl ether (CE) and anionic sodium dodecyl sulfate (SDS) surfactants and polyacrylic acid modified with hydrophobic sidechains mimicking the practically important Carbopol polymer.

Stability of Lipid Coatings on Nanoparticle-Decorated Surfaces.

Lipid membranes supported on solid surfaces and nanoparticles find multiple applications in industrial and biomedical technologies. Here, we explore the mechanisms of the interactions of lipid membranes with nanostructured surfaces with deposited nanoparticles and explain the characteristic particle size dependence of the uniformity and stability of lipid coatings observed . Simulations are performed to demonstrate the specifics of 1,2-dimyristoyl--glycero-3-phosphocholine (DMPC) lipid membrane adhesion to hydrophilic and hydrophobic nanoparticles ranging in size from 1.

Adhesion, intake, and release of nanoparticles by lipid bilayers.

Understanding the interactions between nanoparticles (NP) and lipid bilayers (LB), which constitute the foundations of cell membranes, is important for emerging biomedical technologies, as well as for assessing health threats related to nanoparticle commercialization. Applying dissipative particle dynamic simulations, we explore adhesion, intake, and release of hydrophobic nanoparticles by DMPC bilayers. To replicate experimental conditions, we develop a novel simulation setup for modeling membranes at isotension conditions.

Nanoparticle-Engendered Rupture of Lipid Membranes.

Tension-induced rupture of 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) lipid membranes with encapsulated hydrophobic nanoparticles is elucidated using dissipative particle dynamics simulations. The dynamics of hole formation is studied, and a nanoparticle size-dependent relationship is established for the probability of membrane rupture within a given time as a function of the membrane tension. Two mechanisms of hole formation are explored: homogeneous nucleation and heterogeneous nucleation at the nanoparticle surface.

Coarse-grained model of nanoscale segregation, water diffusion, and proton transport in Nafion membranes.

We present a coarse-grained model of the acid form of Nafion membrane that explicitly includes proton transport. This model is based on a soft-core bead representation of the polymer implemented into the dissipative particle dynamics (DPD) simulation framework. The proton is introduced as a separate charged bead that forms dissociable Morse bonds with water beads.

Adhesion of Phospholipid Bilayers to Hydroxylated Silica: Existence of Nanometer-Thick Water Interlayers.

Lipid bilayers attached to solid surfaces play an important role in bioinspired materials and devices and serve as model systems for studies of interactions of cell membranes with particles and biomolecules. Despite active experimental and theoretical studies, the interactions of lipid membranes with solid substrates are still poorly understood. In this work, we explore, using atomistic molecular dynamics simulations, the equilibrium and stability of a phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine membrane supported on hydroxylated amorphous silica.

Adhesion and Separation of Nanoparticles on Polymer-Grafted Porous Substrates.

This work explores interactions of functionalized nanoparticles (NP) with polymer brushes (PB) in a binary mixture of good and poor solvents. NP-PB systems are used in multiple applications, and we are particularly interested in the problem of chromatographic separation of NPs on polymer-grafted porous columns. This process involves NP flow through the pore channels with walls covered by PBs.

In Situ Growth and Characterization of Metal Oxide Nanoparticles within Polyelectrolyte Membranes.

This study describes a novel approach for the in situ synthesis of metal oxide-polyelectrolyte nanocomposites formed via impregnation of hydrated polyelectrolyte films with binary water/alcohol solutions of metal salts and consecutive reactions that convert metal cations into oxide nanoparticles embedded within the polymer matrix. The method is demonstrated drawing on the example of Nafion membranes and a variety of metal oxides with an emphasis placed on zinc oxide. The in situ formation of nanoparticles is controlled by changing the solvent composition and conditions of synthesis that for the first time allows one to tailor not only the size, but also the nanoparticle shape, giving a preference to growth of a particular crystal facet.

Parametrization of Chain Molecules in Dissipative Particle Dynamics.

This paper presents a consistent strategy for parametrization of coarse-grained models of chain molecules in dissipative particle dynamics (DPD), where the soft-core DPD interaction parameters are fitted to the activities in solutions of reference compounds that represent different fragments of target molecules. The intercomponent parameters are matched either to the infinite dilution activity coefficients in binary solutions or to the solvent activity in polymer solutions. The respective calibration relationships between activity and intercomponent interaction parameter are constructed from the results of Monte Carlo simulation of the coarse-grained solutions of reference compounds.

Coarse-grained model of water diffusion and proton conductivity in hydrated polyelectrolyte membrane.

Using dissipative particle dynamics (DPD), we simulate nanoscale segregation, water diffusion, and proton conductivity in hydrated sulfonated polystyrene (sPS). We employ a novel model [Lee et al. J.

Modeling Proton Dissociation and Transfer Using Dissipative Particle Dynamics Simulation.

We suggest a coarse-grained model for dissipative particle dynamics (DPD) simulations of solutions with dissociated protons. The model uses standard short-range soft repulsion and smeared charge electrostatic potentials between the beads, representing solution components. The proton is introduced as a separate charged bead that forms dissociable bonds with proton receptor base beads, such as water or deprotonated acid anions.

Adhesion of nanoparticles to polymer brushes studied with the ghost tweezers method.

Mechanisms of interactions between nanoparticles (NPs) and polymer brushes (PBs) are explored using dissipative particle dynamics simulations and an original "ghost tweezers" method that emulates lab experiments performed with optical or magnetic tweezers. The ghost tweezers method is employed to calculate the free energy of adhesion. Ghost tweezers represents a virtual harmonic potential, which tethers NP with a spring to a given anchor point.

Morphological transformations in polymer brushes in binary mixtures: DPD study.

Morphological transformations in polymer brushes in a binary mixture of good and bad solvents are studied using dissipative particle dynamics simulations drawing on a characteristic example of polyisoprene natural rubber in an acetone-benzene mixture. A coarse-grained DPD model of this system is built based on the experimental data in the literature. We focus on the transformation of dense, collapsed brush in bad solvent (acetone) to expanded brush solvated in good solvent (benzene) as the concentration of benzene increases.

Self-assembly in Nafion membranes upon hydration: water mobility and adsorption isotherms.

By means of dissipative particle dynamics (DPD) and Monte Carlo (MC) simulations, we explored geometrical, transport, and sorption properties of hydrated Nafion-type polyelectrolyte membranes. Composed of a perfluorinated backbone with sulfonate side chains, Nafion self-assembles upon hydration and segregates into interpenetrating hydrophilic and hydrophobic subphases. This segregated morphology determines the transport properties of Nafion membranes that are widely used as compartment separators in fuel cells and other electrochemical devices, as well as permselective diffusion barriers in protective fabrics.

Oxygen incorporation in rubrene single crystals.

Single crystal rubrene is a model organic electronic material showing high carrier mobility and long exciton lifetime. These properties are detrimentally affected when rubrene is exposed to intense light under ambient conditions for prolonged periods of time, possibly due to oxygen up-take. Using photoelectron, scanning probe and ion-based methods, combined with an isotopic oxygen exposure, we present direct evidence of the light-induced reaction of molecular oxygen with single crystal rubrene.

Calculations of critical micelle concentration by dissipative particle dynamics simulations: the role of chain rigidity.

Micelle formation in surfactant solutions is a self-assembly process governed by complex interplay of solvent-mediated interactions between hydrophilic and hydrophobic groups, which are commonly called heads and tails. However, the head-tail repulsion is not the only factor affecting the micelle formation. For the first time, we present a systematic study of the effect of chain rigidity on critical micelle concentration and micelle size, which is performed with the dissipative particle dynamics simulation method.

Polymer translocation through a nanopore: DPD study.

Translocation of a polymer chain through a narrow pore is explored using 3D explicit solvent dissipative particle dynamics simulation. We study the dependence of the translocation dynamics and translocation time τ on the chain length N, driving force magnitude E, and solvent quality. Two types of driving forces are considered: uniform hydrostatic force, which is applied equally to the chain and solvent particles, and uniform electrostatic force, which is applied selectively to the charged particles in the chain and oppositely charged counterions in the solvent.

Prediction of the Critical Micelle Concentration of Nonionic Surfactants by Dissipative Particle Dynamics Simulations.

Micellization of surfactant solutions is a ubiquitous phenomenon in natural systems and technological processes, and its theoretical description represents one of the cornerstone problems in the physical chemistry of colloidal systems. However, successful attempts of quantitative modeling confirmed by experimental data remains limited. We show, for the first time, that the dissipative particle dynamics with rigorously defined soft repulsion interaction and rigidity parameters is capable of predicting micellar self-assembly of nonionic surfactants.

Interactions of sarin with polyelectrolyte membranes: a molecular dynamics simulation study.

Nanostructured polyelectrolyte membranes (PEMs), which are widely used as permselective diffusion barriers in fuel cell technologies and electrochemical processing, are considered as protective membranes suitable for blocking warfare toxins, including water-soluble nerve agents such as sarin. In this article, we examine the mechanisms of sorption and diffusion of sarin in hydrated PEMs by means of atomistic molecular dynamics simulations. Three PEMs are considered: Nafion, sulfonated polystyrene (sPS) that forms the hydrophilic subphase of segregated sPS-polyolefin block copolymers, and random sPS-polyethylene copolymer.

DPD Simulation of Protein Conformations: From α-Helices to β-Structures.

We suggest a coarse-grained model for DPD simulations of polypeptides in solutions. The model mimics hydrogen bonding that stabilizes α-helical and β-structures using dissociable Morse bonds between quasiparticles representing the peptide groups amenable to hydrogen bonding. We demonstrate the capabilities of the model by simulating transitions between coil-like, globular, α-helical, and β-hairpin configurations of model peptides, varying Morse potential parameters, the hydrophobicities of residue side chains, and pH, which determines the charges of residue side chains.

Translocation dynamics of freely jointed Lennard-Jones chains into adsorbing pores.

Polymer translocation into adsorbing nanopores is studied by using the Fokker-Planck equation of chain diffusion along the energy landscape calculated with Monte Carlo simulations using the incremental gauge cell method. The free energy profile of a translocating chain was found by combining two independent sub-chains, one free but tethered to a hard wall, and the other tethered inside an adsorbing pore. Translocation dynamics were revealed by application of the Fokker-Planck equation for normal diffusion.

Calculation of chemical potentials of chain molecules by the incremental gauge cell method.

The gauge cell Monte Carlo method is extended to calculations of the incremental chemical potentials and free energies of linear chain molecules. The method was applied to chains of Lennard-Jones beads with stiff harmonic bonds up to 500 monomers in length. We show that the suggested method quantitatively reproduces the modified Widom particle insertion method of Kumar et al.

Interactions of phosphororganic agents with water and components of polyelectrolyte membranes.

Interactions of nerve G-agents (sarin and soman) and their simulants DMMP (dimethyl methylphosphonate) and DIFP (diisopropyl fluorophosphate) with water and components of polyelectrolyte membranes are studied using ab initio calculations in conjunction with thermodynamic modeling using the conductor-like screening model for real solvents (COSMO-RS). To test reliability of COSMO-RS calculations, we measured the vapor-liquid equilibrium in DMMP-water mixtures and found quantitative agreement between computed and experimental results. Using COSMO-RS, we studied the interactions of phosphororganic agents with the characteristic fragments of perfluorinated and sulfonated polystyrene (sPS) polyelectrolytes, which are explored for protective clothing membranes.