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Improving hydrophilicity is a key factor for enhancing the biocompatibility of polymer surfaces. Nevertheless, previous studies have reported that poly(2-methoxyethyl acrylate) (PMEA) surfaces demonstrate markedly better biocompatibility than more hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) surfaces. In this work, the origins of the excellent biocompatibility of the PMEA surface are investigated using molecular dynamics (MD) simulations of simplified binary mixtures of acrylate/methacrylate trimers and organic solvents, with n-nonane, 1,5-pentanediol, or 1-octanol serving as the probe organic foulants. The interactions between the acrylate/methacrylate trimers and solvent molecules were evaluated by calculating the radial distribution function (RDF), with the resulting curves indicating that the 2-methoxyethyl acrylate (MEA) trimer has a lower affinity for n-nonane molecules than the 2-hydroxyethyl methacrylate (HEMA) trimer. This result agrees with the experimental consensus that the biocompatibility of PMEA surfaces is better than that of PHEMA surfaces, supporting the hypothesis that the affinity between an acrylate/methacrylate trimer and a foulant molecule in a simplified binary mixture is a significant factor in determining a surface's antifouling properties. The RDF curves obtained for the other two solvent systems exhibited behavior that further highlighted the advantages of the PMEA surfaces as biocompatible polymers. In addition, the validity of employing the second virial coefficient (B2) as a predictor of antifouling properties was explored. The order of the B2 values of different binary mixtures indicated that the MEA trimers have the lowest affinities with n-nonane molecules, which confirms that although PMEA is more hydrophobic than PHEMA, it exhibits better biocompatibility. This analysis demonstrates that the MEA's weaker miscibility with nonpolar foulants contributes to the excellent biocompatibility of PMEA. Thus, B2 is a promising criterion for assessing the miscibility between acrylate/methacrylate materials and nonpolar organic foulants, which indicates the potential for predicting the antifouling properties of acrylate/methacrylate polymer materials by evaluating the value of B2.

The motion of a tiny air bubble in an aqueous solution of cetyl trimethyl ammonium bromide and sodium salicylate (CTAB/NaSal), which forms wormlike micelles, was observed using a high-speed polarization camera. Complex local flow is observed around the bubble surface because the bubble shape deforms repeatedly at 100 Hz. The camera can be used to measure the retardation distribution, which is related to the stress field around the bubble. Different retardation and orientation angle distributions were observed during the contraction and expansion phases. In the contraction phase, a strong retardation distribution appears at the tail of the cusped bubble. The occurrence of uniaxial elongation deformation is considered to be due to the negative wake because they are closely correlated. In contrast, a weak retardation distribution spreads at the upper side of the bubble during the expansion phase, where biaxial extensional deformation occurs due to expansion of the bubble surface. These significant changes in strong elastic stress distributions, which correspond to the orientation angle profiles, can result in increase of bubble rising velocities.

Irrespective of the degree of polymerization, the molecular mobilities of the 2-hydroxyethyl methacrylate (HEMA) moieties are smaller than those of the 2-methoxyethyl acrylate (MEA) moieties. Preventing the polar functional groups of the foulants and materials from forming a hydrogen-bonding network is important to enhance the mobilities of the molecular chains of non-ionic polymeric materials. We speculate that enhancing the mobilities of the molecular chains is key to improving blood compatibility.

Molecular mechanisms of CO2 physical absorption are significant for the development of higher-performance CO2 absorbents. In this study, the free energy profiles for CO2 approaching several types of ethylene glycol (EG)-based solvent molecules and their derivatives (diols, ethers, and alkanes, etc.) were evaluated using molecular dynamics simulations. A desolvation barrier appeared in the free energy profiles in the pure component solvent, corroborating the negative contribution of a void effect on CO2 affinities. The profiles in vacuum were also estimated to investigate the functional group effects in a constituent solvent molecule. The profiles for the EG-based solvent molecules showed similar minimum values to their derivative diols, while the values for their derivative ethers and alkanes were markedly higher. CO2 solubility is certainly determined by two major factors: the specific CO2 affinities of the constituent hydroxyl groups and a steric void effect near an absorbed CO2 molecule.

Suppression of protein adsorption on polymeric interfaces is one of the significant challenges in developing novel biomedical polymers. In this study, the computational design of an antifouling polymer repeat unit is conducted based on a simple approach, whereby the intermolecular affinities between a probe molecule and a polymer repeat unit are evaluated to generate free energy profiles using molecular dynamics simulations. The simplified method affords convenient and theoretical screening of highly antifouling polymer repeat units.

The friction reduction mechanisms of diamond-like carbon (DLC) and H- or F-terminated DLC films were investigated using molecular dynamics (MD) and tight-binding quantum chemistry (TBQC) calculations. Atomistic-scale friction dynamics of both DLC and the surface-terminated DLC model in which the unsaturated bonds on their surface were terminated with H or F atoms were investigated by MD. The F-terminated DLC model showed lower friction than that of the H-terminated DLC model because of the stronger repulsive Coulombic force between F atoms at the surfaces. On the other hand, strong van der Waals interaction acting on the interface was observed for the H-terminated DLC model compared to that for the F-terminated DLC models. TBQC calculation indicates a bonding interaction between the surfaces of DLC, while the antibonding interaction was observed for the surface-terminated DLC model. Those interactions would make the difference in the friction properties among the studied models.

Microscopic behaviors of explicit water molecules on biocompatible zwitterionic self-assembled monolayer (SAM) surfaces were investigated by molecular dynamics simulations. The orientational distribution of water molecules near the surfaces was evaluated to analyze its structural properties. Consequently, water molecules on the zwitterionic SAMs are randomly oriented. In contrast, those near the surface of poly(vinyl alcohol) are highly oriented, resulting from the structured hydrogen bonding network. Microscopic properties of water molecules on the interfaces would have a key role in the suppression of protein adsorption for zwitterionic biomaterials.

Polyzwitterions (PZs), such as carboxybetaine and phosphobetaine polymers, show remarkable suppression of protein adsorption and have potentially widespread application as bioengineering materials....

Dynamics of the CO oxidation NO reduction reaction on thin MgO (100) supported Pd clusters has been studied by quantum chemical molecular dynamics (QCMD). Chemical changes, change of adsorption states, and structural changes were investigated. We observed that CO adsorption occurs molecularly, whereas NO adsorption occurs first molecularly on the Pd cluster, but it is then dissociatively adsorbed on Pd cluster after interacting with CO. Oxygen atoms resulting from the NO dissociation react with adsorbed CO and form CO2 that desorbs from the Pd cluster, whereas the remaining N atom diffuses in the lattice of the Pd cluster. NO dissociation has been found to be the key step for this reaction. Furthermore, from the molecular dynamics and electronic structure calculations, we have identified a number of consequences for the interpretation and modeling of diffusion experiments demonstrating the coverage. As far we know, this is the first QCMD based simulation of the dynamics of CO oxidation, NO reduction, and ...

WOS: 000288825800039, The percolating paths of the carbons and electrolytes in a cathode catalyst layer (CCL) could be successfully visualized in three-dimensions in order to investigate both the electronic and ionic connectivity by modeling a three-dimensional (3-D), meso-scale CCL of a polymer electrolyte membrane fuel cell (PEMFC). The effective Knudsen diffusion coefficients could also be obtained by computing pore tortuosity values. Electrochemical simulation studies were carried out by feeding air at 70 degrees C. Low platinum (Pt) loading (0.1 mg cm(-2)) catalysts with ionomer contents ranging from 14 to 50% were studied. The performance of a PEMFC electrode was affected by the ionomer content which is optimal at about 33%. In this case, both electronic and ionic connectivity produced the broadest active surface area of the Pt catalyst. The polarization drop tendency was in good agreement with the experiment, and this percolation study could successfully explain the existence of an optimum amount of ionomer. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

We theoretically analyzed the formation energy and solvation free energy of four- and six-coordinated Pt(II) and Pt(IV) complexes with three types of ligands (H2O, OH-, and CF3SO3-) as a model of dissolved Pt species to understand the Pt electrocatalyst degradation and dissolution mechanisms. All calculations were performed under the generalized gradient approximation (GGA) with Becke-88 exchange and Lee-Yang-Parr correlation functionals (BLYP). Solvent effects in water were estimated using the conductor-like-screening model (COSMO). The calculated results clarified that Pt(IV) complexes are more energetically favorable than Pt(II) complexes, indicating that the Pt(IV) complexes are more probable as dissolved species than Pt(II) complexes. We also analyzed the geometrical parameters (Pt...O) and atomic charge of O in ligands. These local relaxations about geometry and atomic charge are one of the factors to determine the stability of dissolved Pt species.