Feasibility of the internal standardization in direct determination of arsenic in wine samples by inductively coupled plasma atomic emission spectrometry

In this study, a fast and simple method is proposed for determination of arsenic in wine employing inductively coupled plasma atomic emission spectroscopy and internal standard technique. First Co, Bi, V and Y were evaluated as internal standards to minimize transport interferences. All samples and reference solutions were automatically spiked by autosampler, eliminating the need for manual dilutions. The result demonstrated that vanadium can be used as an internal standard. The experimental parameters (plasma power and nebulization flow rate) were optimized. The relative standard deviations (R.S.D) of measurements varied from 1.1 to 6.0% and 3.2 to 8.7% (n = 12) with and without internal standardization, respectively. Recoveries in the 95-103% range for As spiked samples were obtained.     

Excitation volumetric effects (EVE) in metal-enhanced fluorescence

Metal-Enhanced Fluorescence (MEF) effects from different density silver island films (SiFs) and the effects of far-field excitation irradiance on the observed enhancement of fluorescence were studied. It is shown that MEF non-linearly depends on silver nanoparticle (NP) size/density, reaching a maximum value for SiFs made at a deposition time (DT) of ～5 minutes, i.e. just before SiFs become continuous. Numerical simulations of the silver-islands growing on glass revealed that the near-field magnitude depends non-linearly on size and interparticle distance exhibiting dramatic enhancement at ～10 nm distance between the NPs. In addition, a remarkable effect of modulation in MEF efficiency by far-field excitation irradiance has been observed, which can be correlated well with numerical simulations that show an excitation power volume dependence. The near-field volume changes non-linearly with far-field power. This unique observation has profound implications in MEF, which has rapidly emerged as a powerful tool in the biosciences and ultimately allows for tunable fluorescence enhancement factors.     

Roughness and ordering at the interface of oxidized polystyrene and water

For the first time, atomistically detailed molecular dynamics calculations revealed molecular ordering of the water-oxidized atactic polystyrene (aPS) interface. Both ordering of the water molecules and the phenyl rings occur. In addition, the natural roughness of the surface has been simulated and compared to experimental values. The composition of the simulated aPS films is based on spin-coated aPS films that have been oxidized and characterized experimentally. The aPS surfaces are oxidized with ultraviolet-ozone radiation and have been characterized by XPS, AFM, and water contact angle measurements. XPS measurements show that the oxygen content in the sample increases rapidly with exposure and reaches saturation near 24 at. % of oxygen. The molecular dynamics simulations show smoothening of an hydrophobic aPS surface upon transition from vacuum to water. The smoothening decreases with increasing hydrophilicity. The calculations reveal ordering of oxidized phenyl rings for aPS surfaces in water. The order increases with increasing hydrophilicity. Additionally, we investigated the water structure near the aPS-water interface as a function of the surface hydrophilicity. With increasing hydrophilicity, the density of water at the aPS-water interface increases. The water density profile is steeper in the presence of hydrophobic aPS. The water shows an ordered layer near both the hydrophobic and hydrophilic surfaces; the position of this layer shifts toward the interface with increasing hydrophilicity.     

Ionization energy and energy gap structure of MoSI molecular wires: Kelvin probe, ultraviolet photoelectron spectroscopy, and cyclic voltammetry measurements

The work function W of Mo(6)S(3)I(6) molecular nanowires is determined by Kelvin probe (KP) measurements, UV photoelectron spectroscopy (UPS), and cyclic voltammetry (CV). The values obtained by all three methods agree well, giving W = 4.8 ± 0.1 eV. CV measurements also give a gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of E(g) = 1.2 ± 0.1 eV, in agreement with recent optical measurements, but in disagreement with theoretical calculations, which predict the material to be a metal. The electronic structure of Mo(6)S(3)I(6) suggests use of the material in applications such as bulk heterostructure photovoltaics and transparent electrodes and for molecular electronics devices.     

Sol–gel technology for functional finishing of PES fabric by stimuli-responsive microgel

The possibility of incorporating a stimuli-responsive microgel into a silica matrix by the sol–gel method was studied. This method allows the preparation of a novel class of functional finishes for textile material modification, which is aimed at the creation of simultaneous stimulus-responsive behaviour and functional protective properties. Using a pad-dry-cure method, a thermo- and pH-responsive microgel (PNCS) based on poly-(N-isopropylacrylamide) (poly-NiPAAm) and chitosan was embedded into a silica matrix on a previously activated polyester (PES) fabric. The matrix was composed of a model sol–gel precursor, vinyltrimethoxysilane (VTMS), in combination with hydrophilic fumed silica nanoparticles (SiO₂). Functionalized PES fabric samples were characterised by determining the morphological and chemical properties using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The stimuli (temperature and pH) responsiveness of the functionalized PES fabric was established by measuring its porosity, wicking ability, moisture content, drying rate, water vapour transmission rate and water uptake. In order to assess the washing fastness of the surface modifying systems, the tests were done before and after five consecutive washings. The results showed that sol–gel technology is an appropriate method for the incorporation of PNCS microgel on PES fibre surface. Because of the elasticity of the sol–gel matrix, the VTMS/SiO₂ polysiloxane film had no adverse influence on the swelling/deswelling effect of the PNCS microgel, thus retaining and even enhancing its stimulus response.     

Representation of Hydrogen Atoms in Molecular Dynamics Simulations: The Influence on the Computed Properties of Thin Polystyrene Films

The united atoms (UA) and dummy hydrogen atom (DHA) approaches for molecular dynamics simulations of the interface between oxidized atactic polystyrene (aPS) thin films and water are compared. For both oxidized and non‐oxidized aPS films the polymer density profile decays steepest when using the UA model. The surface roughness of the aPS film and the ordering of the phenyl rings near the surface decrease upon changing from vacuum to water for the UA, but not for the DHA model. This also supports the fact that the non‐oxidized aPS films modeled in DHA representation become less hydrophobic. The water structure close to the interface also suggests that the aPS films modeled using UA are more hydrophobic compared to the aPS films modeled with DHA in the phenyl rings.

     

Rheological Behavior of Some Cationic Polyelectrolytes

The rheological behavior of some cationic polyelectrolytes in aqueous solution is presented. The polyelectrolytes under study consist of polycations that have positive charges (N,N-dimethyl-2-hydroxypropylenammonium chloride) located along the main chain with or without nonpolar side chains (PCA₅D₁ and PCA₅, respectively). This investigation mainly considers the influence of oscillation frequency and temperature on their rheological behavior in salt-free aqueous solution at three polymer concentrations (c_p = 2%, 4%, and 6%) as well as in the presence of low molar mass salt (NaCl). The results indicate the main effect of these parameters was to modify the hydrophobic interactions between the side nonpolar groups of the modified polyelectrolyte. The comparison between the complex viscosity values, at the same polymer concentration, c_p = 4%, for PCA₅D₁ and PCA₅ shows higher values in the whole interval of temperatures under study and a pseudoplastic behavior at temperatures greater than 50°C for the former system.