Biomedical subjects

Wenchuan Wang

Publications and source records attributed to Wenchuan Wang.

8 recordsLinked to original sources

PubMed2006

A Monte Carlo study of spherical electrical double layer of macroions-polyelectrolytes systems in salt free solutions.

A canonical Monte Carlo simulation is performed to investigate the microstructure and the electrical double layer (EDL) of polyelectrolytes around macroions in the bulk systems based on the primitive model. We explore the influences of particles size, chain length, and charge density of polyelectrolytes on the microscopic behavior of the macroions-polyelectrolytes systems. The simulation results show that the surface charge density and the chain length of the polyelectrolytes are two key factors that affect the microstructure of polyelectrolytes around the macroions and potential of mean force between the macroions as well as the zeta potential of the spherical EDL constructed by polyelectrolytes. The high surface charge density of a polyelectrolyte leads to the polyelectrolyte acting as a bridge for the aggregation of macroions, causing the presence of the attraction between macroions. The polyelectrolytes with a long chain length present a cooperativity effect for the adsorption of the polyelectrolytes on the surface of the macroions. Furthermore, the two key factors both induce the overcharge of the macroions. The longer the chain length and the higher surface charge density of the polyelectrolytes, the stronger is the overcharge.

Electrolytes↗

PubMed2006

Adsorption and morphology transition of surfactants on hydrophobic surfaces: a lattice Monte Carlo study.

In this work, we first show that there are only five independent interchange parameters in the surfactant-solvent-interface system in Larson's model, and then adsorption and morphology transition of surfactants on hydrophobic surfaces are studied by extensive lattice Monte Carlo simulations. In our simulations, we found that there exist six adsorbed morphologies: (1) premature admicelle, (2) hemisphere, (3) hemisphere-hemicylinder mixture, (4) wormlike hemicylinder, (5) perforated monolayer, and (6) monolayer. The surface morphologies and the amount of adsorption on hydrophobic surfaces are found to be affected obviously by two interchange parameters. One is the attractive interaction between tail groups and surface (chiTS), and the other is the solubility of head groups in bulk (chiHW). Phase diagrams in chiHW versus chiTS planes for surfactants with different hydrophobicities (chiTW) and for surfactants with different molecular structures are determined in this work, from which the transitions of surface morphologies and adsorption behaviors are discussed.

Journal Article↗

PubMed2006

Theoretical study of CCl(4) adsorption and hydrogenation on a Pt (111) surface.

The adsorption and hydrogenation of carbon tetrachloride (CCl(4)) on a Pt (111) surface have been investigated using density functional theory (DFT). We have performed calculations on the adsorption energies and structures of CCl(4) on four different adsorption sites of a Pt (111) surface using the full adsorbate geometry optimization method. The results show that the adsorption energy of all of the potential sites is less than -17 kcal/mol, which indicates that CCl(4) is physiosorbed on a Pt (111) surface through van der Waals interactions. The dissociation and hydrogenation pathways were investigated by a transition state search. For the Pt(15), Pt(19), and Pt(25) cluster surfaces, the activation energies of dissociation obtained in this work are 15.69, 16.94, and 16.77 kcal/mol, respectively. The hydrogenation of CCl(3). was studied at the on-top site of the Pt(15) cluster, and the calculated activation energy is 5.06 kcal/mol. The small activation energies indicate that the Pt (111) surface has high catalytic activity for the CCl(4) hydrogenation reaction. In addition, the Hirshfeld population analysis reveals that the charge transfer from the Pt (111) surface to the adsorbates occurs in both the dissociation and hydrogenation pathways.

Journal Article↗

PubMed2006

Microstructure and self-assembly of inhomogeneous rigid rodlike chains between two neutral surfaces: A hybrid density functional approach.

We use a hybrid density functional approach to investigate the microstructure and self-assembly of inhomogeneous rigid rodlike chains between two neutral surfaces, i.e., two hard walls. In the calculation, the rodlike molecule is modeled as a rigid rod linearly connected by the tangent sphere beads. The hybrid method combines a single-chain Monte Carlo (MC) simulation for the ideal-gas part of Helmholtz energy and a DFT approach for the excess Helmholtz energy. The DFT approach includes a modified fundamental measure theory for the excluded-volume effect, the first order thermodynamics perturbation theory for chain connectivity, and the mean field approximation for the van der Waals attraction. We investigate the effect of the chain length (i.e., aspect ratio) of the rodlike molecule and the separation between two surfaces on the microstructure and self-assembly of inhomogeneous rigid rodlike chains. For the athermal systems, the rodlike chain fluids present a smaller partitioning coefficient compared to the flexible chain fluids. For the thermal systems, lamellar thin films formed by the rigid rodlike molecules perpendicular to the neutral surface are observed. The effects of the head-head interaction and the separation on the self-assembly of the rodlike chain fluids in the slit are investigated.

Journal Article↗

PubMed2006

The onion-ring structure for Pd-Pt bimetallic clusters.

The onion-ring structure is validated in the Pd-Pt bimetallic clusters of total atom numbers 147 and 309 through the Monte Carlo method by using the second-moment approximation of the tight-binding (TB-SMA) potentials, which is conceived in predicting the possible structures of the bimetallic clusters by He et al. [J. Am. Chem. Soc. 2003, 125, 11034] and Hwang et al. [J. Am. Chem. Soc. 2005, 127, 11140]. In the onion-ring structure, Pd atoms and Pt atoms occupy alternate layers of the clusters. The formation of the onion-ring structure can be associated with the fact that the single Pt impurity is favorable to stay in the subsurface layer and the central part of bimetallic clusters.

Letter↗

PubMed2006

A novel united-atom force field for imidazolium-based ionic liquids.

A novel united-atom (UA) force field is proposed from our previously developed all-atom (AA) force field for the imidazolium-based ionic liquids by the introduction of a coarse-grained method. The Lennard-Jones parameters for CH(2) and CH(3) in alkyls are fitted to match the AA force field, and the partial atomic charges are re-fitted by the one conformation two-step RESP method. The force field is verified by molecular dynamics simulations of pure ionic liquids and the mixture of [bmim][BF(4)] and acetonitrile. The densities, self-diffusion coefficients, vaporization enthalpies, cohesive energy densities, and microscopic structures of both the pure components and mixtures are simulated. The simulated results from the UA force field agree well with those from the AA force field. In addition, the predictive capability of the UA force field for the liquid densities of [C(n)mim][PF(6)] is tested. The UA force field proposed in this work provides a useful tool with good accuracy and much less computational intensity for future molecular design of ionic liquids.

Alkylation↗

PubMed2005

Molecular dynamics simulation of room-temperature ionic liquid mixture of [bmim][BF4] and acetonitrile by a refined force field.

1-Butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) is one of the promising room-temperature ionic liquids. To test the refined force field for [bmim][BF4] proposed in our previously work (J. Phys. Chem. B, 2004, 108, 12978-12989), thermodynamic properties of mixtures of [bmim][BF4](1)+ acetonitrile (2) are presented by using molecular dynamics over the whole concentration range. The calculated densities are in good agreement with the experimental data with deviations less than 2%, indicating the force field is applicable to the mixtures. In addition, the diffusion constants, viscosities, heats of vaporization, cohesive energy densities and excess properties of the mixtures are reported. The microscopic structures are discussed in detail, corresponding to the thermodynamic properties.

Acetonitriles↗

PubMed2002

Grand canonical Monte Carlo simulation for determination of optimum parameters for adsorption of supercritical methane in pillared layered pores.

A grand canonical Monte Carlo (GCMC) method is carried out to determine optimum adsorptive storage pressures of supercritical methane in pillared layered pores. In the simulation, the pillared layered pore is modeled by a uniform distribution of pillars between two solid walls. Methane is described as a spherical Lennard-Jones molecule, and Steele's 10-4-3 potential is used for representing the interaction between the fluid and a layered wall. The site-site interaction is also used for calculating the interaction energy between methane molecules and pillars. An effective potential model that reflects the characteristics of a real pillared layered material is proposed here. In the model, a binary interaction parameter, k(fw), is introduced into the combining rule for the cross-energy parameter for the interaction between the fluid and a layered wall. Based on the experimental results for the Zr-pillared material synthesized and characterized by Boksh, Kikkinides, and Yang, the binary interaction parameter, k(fw), is determined by fitting the simulation results to the experimental adsorption data of nitrogen at 77 K. Then, by taking it as a model of pillared layered material, a series of GCMC simulations have been carried out. The excess adsorption isotherms of methane in a pillared layered pore with three different pore widths and porosities are obtained at three supercritical temperatures T=207.3, 237.0, and 266.6 K. Based on the simulation results at different porosities, various pore widths and different supercritical temperatures, the pillared layered pore with porosity psi=0.94 and pore width hsigma(p)=1.02 nm is recommended as adsorption storage material of supercritical methane. Moreover, the optimum adsorption pressure is determined at a given temperature and a fixed width of the pillared layered pore. For example, at temperature T=207.3 K, the optimum adsorption pressures are 3.1, 3.7, and 4.5 M Pa at H=1.02, 1.70, and 2.38 nm, respectively. In summary, the GCMC method is a useful tool for optimizing adsorption storage of supercritical methane in pillared layered material.

Journal Article↗