Colored LiF: an optical material for all seasons

Colored LiF salt has been always considered a singular optical material among alkali halides and other dielectric crystals for its peculiar characteristics, which in due time have been applied with success in thermoluminescence and laser technology. Lately, while the two previous topics have been revived, new relevant results have been obtained in the optoelectronic field by using both bulk crystals and newly characterized thin films. In practice, miniaturized photoluminescent patterns can be produced rather easily by using low-energy electron beams and soft X-rays. So, LiF salt is becoming a new interesting photonic material with promising developments in basic reasearch and applications as well.     

Comparison of density-functional approaches and Monte Carlo simulations for free planar films of liquid

Density functionals proposed in the literature for describing the behaviour of liquid helium at T =0 K are examined. In so doing, several properties of the ground states of free films of superfluid ⁴ He are calculated by using zero- and finite-range density functional theories and these results are compared to that computed with Monte Carlo simulations. We mainly focus the attention on the energy per particle of the slabs, the surface tension and the width of the liquid-vacuum interfaces, all as a function of the inverse of coverage. The largest differences are found in the case of the surface widths. Received 26 July 1999     

A Direct Experimental Evidence of Collective Electron Resonance Mechanism of Surface Enhanced Infrared Spectroscopy (Seirs)

Abstract

We report here the preliminary results of the surface enhanced transmission infrared spectra of CH₃(CH₂)₇Azo(CH₂)₃COOH monolayers on CaF₂ substrate which was coated by silver island films with different size and distribution. The larger enhancement of absorbance of v(C=O) in COOH residing between silver island gap and small enhancement of absorbance of vibration mode of COO^? located on the silver islands are observed. It give us a direct experimental evidence of the collective electron resonance mechanism of surface enhance infrared spectroscopy (SEIRS), i.e. the decrease of the electromagnetic (EM) coupling reduces the enhancement factor of SEIRS.     

Ab-initio study of doped nanostructures—Mn-doped ultrathin ZnS films

An ab-initio study of the effects of the quantum confinement has been performed for the first time in the ultrathin ZnS films: unpassivated, passivated and the Mn-doped ones. A self-consistent full potential linear muffin tin orbital (FP-LMTO) method has been employed. The studied films have comparatively a large thickness range of 2.7–29.7 Å. The fundamental band gap increases exponentially with decrease in the size of the quantum confinement. The Mn-doped films reveal the localized impurity-induced states within the band gap and also in the conduction band region. The intense optical transitions between the Mn-induced states will appear at about 2.1 eV which is in excellent agreement with the observed peak in the photoluminescence experiments.     

On dewetting dynamics of solid films of hydrogen isotopes and its influence on tritium ß spectroscopy

The dewetting dynamics of solid films of hydrogen isotopes, quench-condensed on a graphite substrate, was measured at various temperatures below desorption by observing the stray light from the film. A schematic model describing the dewetting process by surface diffusion is presented, which agrees qualitatively with our data. The activation energies of different hydrogen isotopes for surface diffusion were determined. The time constant for dewetting of a quench-condensed film at the working temperature of 1.86 K of the mainz neutrino mass experiment was extrapolated. Received 30 December 1999     

Sulfur-Containing Vinyl Monomers. XV. Kinetic Study of Radical Polymerization of Vinyl Mercaptobenzothiazole and Its Copolymerization

A kinetic study of radical polymerization of vinyl mercaptobenzothiazole (VMBT) with α,α′-azobisisobutyonitrile (AIBN) at 60°C was carried out. The rate of polymerization (R_p) was found to be expressed by the rate equation: R_p = k[AIBN]^0.5 [VMBT]^1.0, indicating that the polymerization of this monomer proceeds via an ordinary radical mechanism. The apparent activation energy for overall polymerization was calculated to be 20.9 kcal/mole. Moreover, this monomer was copolymerized with methyl methacrylate, acrylonitrile, vinyl acetate, phenyl vinyl sulfide, maleic anhydride, and fumaronitrile at 60°C. From the results obtained, the copolymerization parameters were determined and discussed.     

Alginate-magnesium aluminum silicate films for buccal delivery of nicotine

Sodium alginate-magnesium aluminum silicate (SA-MAS) dispersions with nicotine (NCT) were prepared at different pHs and characterized for the particle size and zeta potential, NCT adsorbed by MAS, and flow behavior before film casting. The physicochemical properties, NCT content, in vitro bioadhesive property, and NCT release and permeation of the NCT-loaded SA-MAS films were investigated. This study showed that incorporation of NCT into the SA-MAS dispersions caused a change in particle size and flow behavior and that NCT could be adsorbed by MAS. The formation of protonated NCT at acidic and neutral pHs could interact with negatively charged MAS via an electrostatic force, resulting in the formation of NCT-MAS flocculates/complexes that could act as microreservoirs in the films. The NCT-loaded SA-MAS films prepared at pH 5 yielded the highest NCT content due to non-significant loss of NCT during drying. Moreover, pH of the preparation also affected the crystallinity and thermal properties of the films. The NCT release and permeation across the mucosal membrane of the films could be described using a matrix diffusion controlled mechanism. In addition, the NCT-loaded SA-MAS films also possessed a bioadhesive property for adhesion to the mucosal membrane. This finding suggests that the NCT-loaded SA-MAS films composed of numerous NCT-MAS complexes as microreservoirs demonstrated a strong potential for use as a buccal delivery system.     

亚相金属离子与两亲配体LB膜相互作用的研究

The complex formation of 2-hexadecylcarbamoyl-8-hydroxyquinoline(HHQ) monolayers at the air/water interface by reaction with metal ions from the subphase was investigated using X-ray photoelectron spectroscopy. The formation of HHQ-metal complexes leads to the appearance of new peaks assigned to the metal ions. The information on stoichimoetry provided by XPS indicated that a metal ion is coordinated by two HHQ molecules for La3+ and Cd2+ ions, but by one HHQ molecule for Mn2+ and Ni2+ ions.     

The impact of chemical composition on the degradation kinetics of poly(lactic-co-glycolic) acid copolymers cast films in phosphate buffer solution

We have investigated the in vitro degradation of poly(lactic-co-glycolic) acid copolymer with different lactic to glycolic ratio: 50:50, 65:35, 75:25, 95:05 and 100:00 (mol. %). The degradation studies were performed on solvent cast films of controlled thickness and shape. The samples were incubated at 37 °C in phosphate buffered saline solution. The degradation was followed using potentiometry, light microscopy, gravimetry, size exclusion chromatography and differential scanning calorimetry. The same degradation process, as discussed in detail in our previous article for PLGA 50:50 (E. Vey et al., J. of Polym. Deg. and Stab. 2008, 93, 1896-1876), was observed for all the samples investigated, however the time scale over which the different events/degradation steps were observed increased with increasing lactic content of the polymer. The glass transition temperatures of the films increase with lactic content and are thought to have a significant impact on the rate of diffusion of water into the films - the higher the glass transition the slower the diffusion of water - and therefore on the degradation dynamics of the films. Kinetic parameters were extracted from the acid release, molecular weight and mass loss data. In each case linear correlations between the rate constants extracted and the lactic content of the polymer were found. The overall degradation rate of the films was found to decrease with increasing lactic content.     

Environmentally degradable LLDPE/esterified styrene-maleic anhydride (ESMA) blends

LLDPE was blended with esterified styrene-maleic anhydride (ESMA) to improve the environmental degradation characteristics of LLDPE. ESMA was synthesized by esterifying styrene maleic anhydride (SMA) with n-decanol. LLDPE was blended with ESMA (EDP blends) and SMA separately in a single screw extruder by melt mixing. Composition of ESMA was varied from 20 to 40 wt% in the blends. LLDPE grafted with glycidyl methacrylate (LLDPE-g-GMA) was used as compatibilizer to improve the compatibility. Scanning electron photomicrograph (SEM) of cryofractured impact specimens showed significant reduction in domain size and uniform distribution of ESMA in LLDPE matrix in presence of compatibilizer in 70/30 blends. Environmental degradability was assessed by subjecting the films to soil burial test and exposure to buffer solution of different pH. Environmental degradation was followed by measuring the periodic change in weight of the blend samples. Films were exposed to accelerated and natural weathering and photodegradation was assessed by noting the embrittlement time of the film. Films of compatibilized blends fragmented at a faster rate than the films of uncompatibilized blend. Carbonyl index of films subjected to natural weathering was also found to be higher than that for the virgin LLDPE films.