Complex role of chemical nature and tacticity in the adsorption free energy of carboxylic acid polymers at the oil-water interface: molecular dynamics simulations.

Scientific understanding of the molecular structure and adsorption of polymers at oil-water liquid interfaces is very limited. In this study the adsorption free energy at the oil (CCl)-water interface was estimated using umbrella sampling molecular dynamics simulations for six carboxylate type vinyl polymers differing in hydrophobic nature and tacticity: and poly(acrylic acid) (-PAA, -PAA), and poly(methacrylic acid) (-PMA, -PMA), and and poly(ethylacrylic acid) (-PEA, -PEA). Δ values are in the order -PMA < -PEA < -PEA < -PAA < -PAA < -PMA.

Conformations and Solvation of Synthetic Polymers in Water by Generalized Born Implicit-Solvent Molecular Dynamics Simulations: Stereoisomers of Poly(acrylic acid) and Poly(methacrylic acid).

We present the GB-OBC model as an approach for implicit-solvent MD simulations of a synthetic macromolecule in water. The model is tested and found to be successful in reproducing the chain dimensions and predicting the free energy of solvation of carboxylic acid vinyl polymers. The influence of stereochemistry and the hydrophobic nature of the polymer was investigated as a function of chain length (20 < < 600) for poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMA).

Molecular dynamics simulations of structure and dynamics in aqueous solution of neutral and ionized derivatives of poly(F): methyl, n-propyl, and isopropyl substitutions.

Chain dimensions, intermolecular structure and hydration of a series of uncharged and cationic poly(vinyl amine) [PVAm] linear polymers having hydrophobic substituent methyl, n-propyl, and isopropyl in the monomer are studied in aqueous solution by molecular dynamics simulations. A conformational transition occurs in the degree of ionization, α, range 0.3 to 0.

Structure and dynamics of an aqueous solution containing poly-(acrylic acid) and non-ionic surfactant octaethylene glycol n-decyl ether (CE) aggregates and their complexes investigated by molecular dynamics simulations.

A detailed molecular dynamics simulation study of the self-assembly, intermolecular structure and thermodynamic behavior of an aqueous solution of non-ionic surfactant octa ethylene glycol n-decyl ether (CE) in the presence of a non-ionic polar polymer poly(acrylic acid) PAA is presented. The aggregation number N and concentration of surfactant C in the simulation systems were varied in the range 0.01-0.

Molecular View into the Cyclodextrin Cavity: Structure and Hydration.

We find, through atomistic molecular dynamics simulation of native cyclodextrins (CDs) in water, that although the outer surface of a CD appears like a truncated cone, the inner cavity resembles a conical hourglass because of the inward protrusion of the glycosidic oxygens. Furthermore, the conformations of the constituent α-glucose molecules are found to differ significantly from a free monomeric α-glucose molecule. This is the first computational study that maps the conformational change to the preferential hydrogen bond donating capacity of one of the secondary hydroxyl groups of CD, in consensus with an NMR experiment.

Selective production of phenols from lignin via microwave pyrolysis using different carbonaceous susceptors.

With an objective to improve the yield and selectivity of phenols in pyrolysis bio-oil from lignin, this study investigates the effects of mass ratio of lignin-to-susceptor and different types of susceptors (activated carbons of different particle sizes, charcoal and graphite) in microwave pyrolysis. Pyrolysis was carried out in a batch microwave reactor, and the temperature profiles at different operating conditions were captured. Increasing the mass of susceptor with respect to lignin enhanced the bio-oil yield, and maximum yield of 66 wt% with >90% selectivity to phenols was obtained with 10 g lignin:90 g activated carbon.

Factors responsible for the aggregation behavior of hydrophobic polyelectrolyte PEA in aqueous solution studied by molecular dynamics simulations.

Self-association (i.e. interchain aggregation) behavior of atactic poly(ethacrylic acid) PEA in dilute aqueous solution as function of degree-of-neutralization by Na counter-ions (i.

Effect of salt valency and concentration on structure and thermodynamic behavior of anionic polyelectrolyte Na-polyethacrylate aqueous solution.

The intermolecular structure and solvation enthalpy of anionic polyelectrolyte atactic Na-polyethacrylate (PEA) in aqueous solution, as a function of added salt concentration C (dilute to concentrated) and valency (NaCl versus CaCl), were investigated via molecular dynamics simulations with explicit-ion-solvent and atomistic polymer description. An increase in C leads to a decrease in α, which stabilizes to a constant value beyond critical C . A significant reduction in R in the presence of CaCl salt was observed, due to ion bridging of PEA by Ca ions, in agreement with results available in literature on other similar polycarboxylates.

Polyelectrolyte conformational transition in aqueous solvent mixture influenced by hydrophobic interactions and hydrogen bonding effects: PAA-water-ethanol.

Molecular dynamics simulations of poly(acrylic acid) PAA chain in water-ethanol mixture were performed for un-ionized and ionized cases at different degree-of-ionization 0%, 80% and 100% of PAA chain by Na(+) counter-ions and co-solvent (ethanol) concentration in the range 0-90vol% ethanol. Aspects of structure and dynamics were investigated via atom pair correlation functions, number and relaxation of hydrogen bonds, nearest-neighbor coordination numbers, and dihedral angle distribution function for back-bone and side-groups of the chain. With increase in ethanol concentration, chain swelling is observed for un-ionized chain (f=0) and on the contrary chain shrinkage is observed for partially and fully ionized cases (i.

Molecular Dynamics Simulations of Adsorption of Poly(acrylic acid) and Poly(methacrylic acid) on Dodecyltrimethylammonium Chloride Micelle in Water: Effect of Charge Density.

We have investigated the interaction of dodecyltrimethylammonium chloride (DoTA) micelle with weak polyelectrolytes, poly(acrylic acid) and poly(methacrylic acid). Anionic as well as un-ionized forms of the polyelectrolytes were studied. Polyelectrolyte-surfactant complexes were formed within 5-11 ns of the simulation time and were found to be stable.

Effect of chemical substituents on the structure of glassy diphenyl polycarbonates.

Polycarbonates offer a wide variety of physical property behavior that is difficult to predict due to complexities at the molecular scale. Here, the physical structure of amorphous glassy polycarbonates having aliphatic and cycloaliphatic chemical groups is explored through atomistic simulations. The influence of chemical structure on solubility parameter, torsion distributions, radial distribution function, scattering structure factor, orientation distributions of phenylene rings and carbonate groups, and free volume distributions, leading to interchain packing effects, are shown.

The thickness of 18-MEA on an ultra-high-sulfur protein surface by molecular modeling.

The use of computational chemistry techniques via molecular modeling software provides additional support to the hair surface model by Negri et al. (1) and refines the thickness of the 18-methyl eicosanoic acid (18-MEA) lipid layer attached by thioester linkages to an ultra-high-sulfur protein (UHSP) at 1.08 ± 0.