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Using Langevin dynamics simulation, we study the surface switching properties of mixed polyelectrolyte brushes made of 4-arm stars and linear chains. The length and average charge fraction of the linear chains, Bjerrum length (a characteristic length to quantify the strength of the electrostatic interaction), the solvent quality as well as external electric fields were used as controlling parameters to induce sharp transitions of molecular conformations, leading to brush surfaces dominated by end monomers of linear chains or stars. Phase diagrams in terms of the length and charge fraction of linear chains demarcating different regimes of the composition of brush surfaces were constructed under different external electric fields. Besides the different regimes in the phase diagram of mixed brushes under a stretching electric field or in the absence of electric fields, a new regime, which is featured by the linear chains with very low charge fraction sandwiched between the collapsed and un-collapsed stars, emerges in the phase diagram under a collapsing electric field. The stratification within the brush layer of the mixed brushes under external electric fields was also investigated. [ABSTRACT FROM AUTHOR]

The adsorption of flexible polyelectrolytes (PEs) with the annealed charge distribution onto an oppositely charged sphere immersed in a PE solution is studied numerically with the continuum self-consistent field theory. The numerical study reveals interesting scaling relationships between the boundary layer thickness and the surface charge density of the sphere as well as the degree of ionization of the monomers of the PE chains in the bulk solution. The dependences of the degree of charge compensation of the total amount of charges on adsorbed PE chains over the surface charges upon various system parameters are investigated. In particular, the effect of the radius of the charged sphere on the degree of charge compensation is carefully examined. The numerical study indicates that the curvature effect is closely related to the surface electric potential of the charged sphere. Moreover, in this study of the adsorption of PEs with the annealed charge distribution, a comparison with the corresponding case for PEs with the smeared charge distribution in terms of the boundary layer scaling law and the degree of charge compensation is also presented. [ABSTRACT FROM AUTHOR]

The continuum self-consistent field (SCF) theory is applied to the study of the adsorption of flexible polyelectrolytes (PEs) onto the surfaces of two parallel and infinitely long charged columns, taking into account the short-range monomer-surface non-Coulombic interaction. Due to the complex interplay between the electrostatic and surface interactions, very interesting PE adsorption behaviors in terms of the degree of charge compensation and the bridging chain conformation are found from the numerical solution of the SCF equations. The screening-enhanced salt effect and the permanent adsorption of PEs, irrespectively of the salt concentration, emerge in the presence of the monomer-surface non-electrostatic interaction. The numerical results reveal that, for relatively weak monomer-surface interactions, the degree of charge compensation decreases with increasing monomer-surface interaction. Numerical result shows that, for the strength of monomer-surface interaction above the desorption-adsorption critical value and in a salt-free solution, the total amount of the adsorbed PE chains is linearly proportional to the surface charge density in the high PE charge fraction regime. [ABSTRACT FROM AUTHOR]

We study the dynamics and equilibrium profile shapes of contact lines for wetting in the case of a spatially inhomogeneous solid wall with stripe defects. Using a phase-field model with conserved dynamics, we first numerically determine the contact line behavior in the case of a stripe defect of varying widths. For narrow defects, we find that the maximum distortion of the contact line and the healing length is related to the defect width, while for wide defects, it saturates to constant values. This behavior is in quantitative agreement with the experimental data. In addition, we examine the shape of the contact line between two stripe defects as a function of their separation. Using the phase-field model, we also analytically estimate the contact line configuration and find good qualitative agreement with the numerical results. [ABSTRACT FROM AUTHOR]

The phase-separation dynamics of a ternary mixture (A, B and C) coupled with a reversible chemical reaction between the two constituents A and B is presented. It is demonstrated that the free-energy functional form of time-dependent-Ginzburg-Landau equation describing the phase-separation dynamics of the ternary mixture coupled with a reversible chemical reaction is similar to that of the mixture composed of a block copolymer and a homopolymer. Our simulation study reveals that for the case of equal forward and backward reaction rates, the lamellar thickness scales with the reaction rate constant as a single power law λ[sub L]∼Γ[sup -0.22], regardless of high or low reaction rate regimes. This study sheds insight to the unique features of the involvement of chemical reaction in the phase separation of the ternary mixture. If chemical reaction and phase separation take place simultaneously, the different pattern evolutions at high and low reaction rate constants are originated from the balance between the domain coarsening due to phase separation and the breakup of the continuous phase due to the chemical conversion. The different pattern evolution at high and low reaction rate constants when chemical reaction lags behind phase separation can be interpreted in terms of the discrepancy between the domain sizes at the time step immediately before the turning on of the chemical reaction and the inherent lamellar thickness. It is also pointed out that the crossover of the ternary mixture from one phase region to another, due to the concentration change between A and B, might generate interesting steady-state domain patterns. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Background & Objectives: Biapenem is a newly developed carbapenem to treat moderate and severe bacterial infections. This multicenter, randomized, parallel-controlled clinical trial was conducted to compare the clinical efficacy, bacterial eradication rates and safety of biapenem and meropenem in the treatment of bacterial lower respiratory tract infections and urinary tract infections (UTIs) at nine centres in China., Methods: Patients diagnosed with bacterial lower respiratory tract infections or UTIs were randomly assigned to receive either biapenem (300 mg every 12 h) or meropenem (500 mg every 8 h) by intravenous infusion for 7 to 14 days according to their disease severity. The overall clinical efficacy, bacterial eradication rates and drug-related adverse reactions of biapenem and meropenem were analyzed., Results: A total of 272 enrolled cases were included in the intent-to-treat (ITT) analysis and safety analysis. There were no differences in demographics and baseline medical characteristics between biapenem group and meropenem group. The overall clinical efficacies of biapenem and meropenem were not significantly different, 94.70 per cent (125/132) vs. 93.94 per cent (124/132). The overall bacterial eradication rates of biapenem and meropenem showed no significant difference, 96.39 per cent (80/83) vs. 93.75 per cent (75/80). Drug-related adverse reactions were comparable in biapenem and meropenem groups with the incidence of 11.76 per cent (16/136) and 15.44 per cent (21/136), respectively. The most common symptoms of biapenem-related adverse reactions were rash (2.2%) and gastrointestinal distress (1.5%)., Interpretation & Conclusions: Biapenem was non-inferior to meropenem and was well-tolerated in the treatment of moderate and severe lower respiratory tract infections and UTIs.