Local Structure of Nonuniform Fluid Mixtures Containing Associating and Chainlike Molecules from a Multilayer Quasichemical Model.

In this work, we develop a theory for predicting details of the local structure in nonuniform multicomponent fluids that may contain chainlike and associating components. This theory is an extension─to the fluid interfaces and mesoscopic structures of different geometry─of the multilayer quasichemical model originally proposed by Smirnova to describe liquid solution in the vicinity of a planar solid wall. The basis of the theory is the "cut-and-bond" approach, much in spirit of SAFT, where an infinite attraction between the separated monomeric units of a chainlike molecule mimics the chemical bonds of the chain.

Modeling Micellar Growth and Branching in Mixtures of Zwitterionic with Ionic Surfactants.

Zwitterionic surfactants are widely applied as drag-reducing or thickening agents because their aggregation patterns may drastically change in response to variations of the system composition or external stimuli, which provides controllable viscoelasticity. For predicting aggregation behavior of surfactant mixtures, classical molecular thermodynamic models have been widely used. Particularly, the results of modeling have been reported for zwitterionic/ionic surfactant mixtures.

Transmembrane potential in vesicles formed by catanionic surfactant mixtures in an aqueous salt solution.

The transmembrane potential plays a key role in a multitude of natural and synthetic systems because it is the driving force for the flow of mobile charged species across the membranes. We develop a molecular thermodynamic theory to study the transmembrane potential of metastable and equilibrium vesicles as a function of the vesicle structural parameters, and salinity and acidity of the surrounding aqueous solution. We show that addition of salt to the external solution may reverse the sign of the transmembrane potential, indicating the reversal of sign of the net charges accumulated in the vesicle interior and exterior.

Theoretical study on the absorption of carbon dioxide by DBU-based ionic liquids.

In this article, 20 ns molecular dynamic (MD) simulations and density functional theory (DFT) were used to investigate the absorption of CO2 molecules by some functionalized 1,8-diazabicyclo[5,4,0]-udec-7-ene (DBU)-based ILs. According to the MD results, the highest coordination number for NC is observed in the case of [DBUH+][Im-], which indicates that the functionalization of the imidazole anion by different alkyl groups decreases the interaction ability of the anion with CO2 molecules. The addition of water molecules to the ILs decreases the ability of the anion to interact with CO2 because of the hydrogen bond formation between the imidazole anions and water.

Molecular thermodynamic modeling of a bilayer perforation in mixed catanionic surfactant systems.

Perforated bilayers play an essential role in biology and in surface science. Here, we extend the classical aggregation model of catanionic surfactant mixtures to describe perforations in a self-assembled bilayer in aqueous salt. The model predicts that changing solution salinity and anionic-to-cationic surfactant ratio may lead to the spontaneous formation of pores in the bilayer and to the assembly of a micellar network.

Distribution of zwitter-ionic tryptophan between the micelles of 1-dodecyl-3-methyl imidazolium and aqueous medium from molecular dynamic simulation.

Ionic liquids that form micelles have great potential as drug carriers and separating agents for bioactive substances. For such applications, a key issue is the distribution of the target substance between the micelle and its environment. We perform MD simulations to study solubilization of zwitter-ionic tryptophan in micelles of 1-dodecyl-3-methylimidazolium bromide.

Driving Force for Spontaneous Perforation of Bilayers Formed by Ionic Amphiphiles in Aqueous Salt.

Spontaneous perforation of amphiphilic membranes is important in both living matter and technology because of an impact on functions of biological membranes and shape transitions of self-assembling structures. Nevertheless, no definite molecular mechanism has been established so far even for simple ionic surfactant systems. We show that spontaneous perforation of a bilayer formed by an ionic amphiphile is driven by electrostatics.

Association Equilibrium for Cross-Associating Chains in a Good Solvent: Crowding and Other Nonideality Effects.

Association equilibrium has been studied by molecular dynamics (MD) for mixtures of cross-associating molecules (n-decamer+p-dimer and n-decamer+p-decamer) in a good solvent. Each monomer of n-decamers carries an associative site (n-sticker); each molecule of the second component contains two terminal associative sites (p-stickers). To model the univalent association between the n-sticker and the p-sticker, a technique based on introduction of dummy atoms has been used.

Modeling of the effects of ion specificity on the onset and growth of ionic micelles in a solution of simple salts.

A new version of the molecular thermodynamic model has been developed that takes into account the effect of ion specificity on the free energy of aggregation. The specificity of salt is reflected by differences in the bare ionic sizes and polarizabilities leading to the difference in the dispersion interaction of ions with the aggregate. The model also contains parameters that characterize the compactness of ionic pairs formed between a mobile ion and surfactant's headgroup.

Molecular thermodynamic modeling of the morphology transitions in a solution of a diblock copolymer containing a weak polyelectrolyte chain.

For a solution of the diblock copolymer composed of a hydrophobic block and a weak polyelectrolyte block, we obtain regions of stable aggregate morphologies in pH-solution salinity plane with the aid of the self-consistent field theory in the strong-segregation approximation. Lamellar, cylindrical, branched cylindrical, and spherical aggregates have been considered in the large interval of pH and salinity. The morphology stability maps are obtained to help control self-assembly of aggregates by variation of pH and salinity of the medium.

Molecular thermodynamics for micellar branching in solutions of ionic surfactants.

We develop an analytical molecular-thermodynamic model for the aggregation free energy of branching portions of wormlike ionic micelles in 1:1 salt solution. The junction of three cylindrical aggregates is represented by a combination of pieces of the torus and bilayer. A geometry-dependent analytical solution is obtained for the linearized Poisson-Boltzmann equation.