Size control of phase‐separated liquid crystal droplets in a polymer matrix based on the phase diagram

When a mixture of liquid crystal (LC) and photo reactive monomer is irradiated by UV light, polymerization occurs and LC droplets form through phase separation, producing polymer dispersed LCs (PDLCs). Although size control of LC droplets and reduced amounts of LC in PDLC films are important in applications, precise size control of LC droplets at a low LC fraction has not yet been accomplished. In this study, the phase diagrams of the LC/initial monomer and the LC/polymer during polymerization were used to control LC droplet size at various LC fractions. Both the relative position of the sample in the initial phase diagram and the shift of the phase separation line during polymerization were shown to be important in determining the size of LC droplets. Our results are expected to provide a new strategy for precise size control of LC droplets especially at a low LC fraction range, which would be a great help for PDLC applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Determination of aminoglycoside residues by liquid chromatography and tandem mass spectrometry in a variety of matrices

A quantitative LC–MS/MS method was developed for the determination of 13 commonly used aminoglycoside antibiotics in meat (pork muscle, fish, and veal livers and kidneys). The proposed method is sufficiently sensitive and highly selective. Unlike other previously reported methods, it uses a simple clean-up procedure based on a strong cation-exchange solid-phase cartridge that permits high sample extract loading volumes. A unique elution regime based on a volatile buffer at intermediately high pH value in combination with an organic solvent provides quantitative elution of the various aminoglycosides. This methodology ensured that neither a breakthrough of weakly retained aminoglycosides (e.g. spectinomycin) nor the incomplete elution of strongly retained analytes (e.g. neo- and gentamycin) is observed. The single-step clean-up is fast and produces clean extracts that minimize matrix-related signal suppression in the electrospray interface.     

A thermodynamic and dynamic subgrid closure model for two‐material cells

A general and robust subgrid closure model for two‐material cells is proposed. The conservative quantities of the entire cell are apportioned between two materials, and then, pressure and velocity are fully or partially equilibrated by modeling subgrid wave interactions. An unconditionally stable and entropy‐satisfying solution of the processes has been successfully found. The solution is valid for arbitrary level of relaxation. The model is numerically designed with care for general materials and is computationally efficient without recourse to subgrid iterations or subcycling in time. The model is implemented and tested in the Lagrange‐remap framework. Two interesting results are observed in 1D tests. First, on the basis of the closure model without any pressure and velocity relaxation, a material interface can be resolved without creating numerical oscillations and/or large nonphysical jumps in the problem of the modified Sod shock tube. Second, the overheating problem seen near the wall surface can be solved by the present entropy‐satisfying closure model. The generality, robustness, and efficiency of the model make it useful in principle in algorithms, such as ALE methods, volume of fluid methods, and even some mixture models, for compressible two‐phase flow computations. Copyright © 2013 John Wiley & Sons, Ltd.     

Inductive effect for the phase stability in hydrogen bonded liquid crystals,x-(p/m)BA:9OBAs

A new series of hydrogen bonded liquid crystal (HBLC) complexes, made up with substituted benzoic acids (BAs) and nonyloxy benzoic acid, viz., x-(p/m)BA:9OBAs are reported for x = F, Cl, Br and –CH₃ substituted at para (p) or meta (m) positions of BA moiety. Proton nuclear magnetic resonance (¹H-NMR) spectrum confirms the HBLC complex. Infra red (IR) spectrum confirms linear, double and complementary type of hydrogen bonding (HB) between x-(p/m)BAs and 9OBA. The liquid crystal (LC) phases are characterised by polarisation optical microscopy (POM) and differential scanning calorimetry (DSC) techniques. x-(p/m)BA:9OBA exhibit N, C and G LC phase variance. HB induces tilted phases and enhances LC phase stability. The influence of configuration, size, electronegativity, electron directing capacity and inductive nature of substituent (x) is investigated for the stability of LC phases. An overview of the LC phase data indicates predominant ‘negative inductive effect’ in HBLCs with electron withdrawing substituents. Inductive effect operates effectively for para substitutions. Results are discussed in the wake of reports in other HBLCs.     

Development and validation of a high‐performance liquid chromatography method for determination of lisinopril in human plasma by magnetic solid‐phase extraction and pre‐column derivatization

A sensitive, reliable and simple HPLC method was developed for the determination of lisinopril in human plasma. The method consists of extraction and clean‐up steps based on magnetic solid‐phase extraction and pre‐column derivatization with a fluorescent reagent. The mobile phase consisted of a mixture of methanol–sodium dihydrogen phosphate (pH 3.0; 0.005 m ; 75:25, v/v). The flow rate was set at 0.7 mL/min. Fluorescence detection was performed at 470nm excitation and 530nm emission wavelengths. Total chromatography run time was 5 min. The average extraction recovery of lisinopril and fluvoxamine (internal standard) was ≥82.8%. The limits of detection and quantification were determined as 1 and 3 ng/mL respectively. The method exhibited a linear calibration line over the concentration range of 3–1000 ng/mL with coefficient of determination (r²) of ≥0.98. The within‐run and between‐run precisions were satisfactory with values of CV of 1.8–12.8% (accuracy from 99.2 to 94.7%) and 2.4–13.7% (accuracy from 99.5 to 92.2%), respectively. These developments led to considerable improvement in method sensitivity and reliability. The method was validated according to the US Food and Drug Administration guidelines. Therefore, it can be considered as a suitable method for determination of lisinopril in plasma samples.     

A hierarchical porous carbon membrane from polyacrylonitrile/polyvinylpyrrolidone blending membranes: Preparation,characterization and electrochemical capacitive performance

Novel hierarchical porous carbon membranes were fabricated through a simple carbonization procedure of well-defined blending polymer membrane precursors containing the source of carbon polyacrylonitrile (PAN) and an additive of polyvinylpyrrolidone (PVP), which was prepared using phase inversion method. The as-fabricated materials were further used as the active electrode materials for supercapacitors. The effects of PVP concentration in the casting solution on structure feature and electrochemical capacitive performance of the as-prepared carbon membranes were also studied in detail. As the electrode material for supercapacitor, a high specific capacitance of 278.0 F/g could be attained at a current of 5 mA/cm² and about 92.90% capacity retention could be maintained after 2000 charge/discharge cycles in 2 mol/L KOH solution with a PVP concentration of 0.3 wt% in the casting solution. The facile hierarchical pore structure preparation method and the good electrochemical capacitive performance make the prepared carbon membrane particularly promising for use in supercapacitor.     

Face-centred cubic to body-centred cubic phase transformation under [1 0 0] tensile loading

Molecular dynamics simulation was used to verify a speculation of the existence of a certain face-centred cubic (FCC) to body-centred cubic (BCC) phase transformation pathway. Four FCC metals, Ni, Cu, Au and Ag, were stretched along the [1?0?0] direction at various strain rates and temperatures. Under high strain rate and low temperature, and beyond the elastic limit, the bifurcation of the FCC phase occurred with sudden contraction along one lateral direction and expansion along the other lateral direction. When the lattice constant along the expansion direction converged with that of the stretched direction, the FCC phase transformed into an unstressed BCC phase. By reducing the strain rate or increasing the temperature, dislocation or ‘momentum-induced melting’ mechanisms began to control the plastic deformation of the FCC metals, respectively.     

Global hysteresis in ferroelectrics with incommensurate phases

A review of the basic experimental results connected with the formation of long-living metastable states in the incommensurate phases of ferroelectric crystals and related phenomena is given. The interpretation and appropriate physical mechanisms underlying the global hysteresis phenomena associated with these states are considered.