A. Chrissanthopoulos

Temperature induced changes on the structure and the dynamics of the “tetrahedral” glasses and melts of ZnCl2 and ZnBr2

Glassy, supercooled, and molten ZnCl2 and ZnBr2 have been studied by Raman spectroscopy over the broad temperature range −196 to 800 °C in an effort to follow in detail the structural changes caused by temperature variation. A systematic study has also been undertaken for the corresponding crystalline polymorphs showing that each material exists in only one crystalline phase if water traces are not present. The reduced isotropic and anisotropic Raman spectra of the ZnCl2 and ZnBr2 glasses and melts are isomorphous. Unusually drastic changes of the relative intensities of particular bands occur with temperature in the reduced isotropic spectra. A comparison between the spectral features of crystals, glasses, and melts has revealed that the network structure of the glasses and melts consists of ZnX4/2 (X=Br,Cl) tetrahedra bound to each other by apex- and edge-bridged halides. The substructure of the glass/melt is formed by mixing a variety of tetrahedra participating in “open,” “cluster,” and “chain” networ...

Enhanced Raman gain of Ge–Ga–Sb–S chalcogenide glass for highly nonlinear microstructured optical fibers

The off-resonance Raman spectra of As2S3, GeS2, Ge25Ga5S70, Ge23As12S65, Ge23Sb12S65, and Ge17Ga4Sb10S69 chalcogenide glasses have been recorded and the corresponding Raman gain coefficients have been calculated in order to evaluate the role of Ge, Ga, Sb, and As on a novel Ge17Ga4Sb10S69 glass proposed for highly nonlinear microstructured optical fibers. We calculated the Raman response functions of As2S3n2=2.3×10−17 m2/W, G∼2.78×10−11 m/W; and Ge17Ga4Sb10S69 n2=1.8×10−17 m2/W, G∼1.57×10−11 m/W glasses. The supercontinuum generation of a three-air-hole Ge17Ga4Sb10S69 fiber was simulated, challenging the properties of a similar fiber design made of As2S3 chalcogenide glass. We calculated the zero dispersion wavelengths of Ge17Ga4Sb10S69 fibers with the core diameters of 1.2, 1.5, and 2.0 μm at λ=1.48, 1.66, and 1.75 μm in comparison with λ=1.60, 1.87, and 1.98 μm obtained for As2S3 fibers.

Effect of cluster size of chalcogenide glass nanocolloidal solutions on the surface morphology of spin-coated amorphous films

Amorphous chalcogenide thin film deposition can be achieved by a spin-coating technique from proper solutions of the corresponding glass. Films produced in this way exhibit certain grain texture, which is presumably related to the cluster size in solution. This paper deals with the search of such a correlation between grain size of surface morphology of as-deposited spin-coated As33S67 chalcogenide thin films and cluster size of the glass in butylamine solutions. Optical absorption spectroscopy and dynamic light scattering were employed to study optical properties and cluster size distributions in the solutions at various glass concentrations. Atomic force microscopy is used to study the surface morphology of the surface of as-deposited and thermally stabilized spin-coated films. Dynamic light scattering revealed a concentration dependence of cluster size in solution. Spectral-dependence dynamic light scattering studies showed an interesting athermal photoaggregation effect in the liquid state.

Probing the structure of GdCl3–KCl melt mixtures by electronic absorption spectroscopy of the hypersensitive f←f transitions of Ho3+ and by Raman spectroscopy

The structure of molten mixtures of GdCl3–KCl at different compositions and temperatures has been investigated by f←f electronic absorption and Raman spectroscopy. The systematics of the Raman spectra indicate that in melt mixtures rich in KCl the predominant species are GdCl63− octahedra, while at higher GdCl3 mole fraction edge bridging of the octahedra occurs. At all compositions including the pure GdCl3 melt the gadolinium coordination is presumably six-fold. The electronic absorption spectra of Ho3+ in molten LiCl, CsCl and LiCl–KCl eutectic have been measured. The data suggest that the predominant factor affecting the intensities of the Ho3+ hypersensitive transitions is the degree of octahedral distortions in conjunction with the overall symmetry around the HoCl63−. Changes of the electron donating ability of the Cl− ligands by the polarizing power of the alkali metal counter cations do not affect drastically the f←f intensities. Electronic absorption spectral measurements of Ho3+ centers in different GdCl3–KCl molten mixtures show that the hypersensitive band intensities increase with increasing GdCl3 mole fraction. These changes are attributed to increasing octahedral distortion imposed on the HoCl63− octahedra by the host melt. Furthermore, the spectra indicate that there are no drastic coordination changes occurring as we go from the mixtures dilute in GdCl3 to the pure GdCl3 melt, and support the Raman data view that the coordination of Gd3+ is six-fold at all compositions.

Calcite overgrowth on carboxylated polymers

The kinetics of calcite crystallization on polymers containing –C ¼ O, functional group was investigated by the constant composition method. The apparent order for the crystallization process was found to be 2.270.3 indicative of a surface diffusion controlled mechanism. The number of ions forming the critical nucleus was found to be 3–6. These values were confirmed by quantum mechanical calculations using the PM3 method of the MOPAC program package. The surface energy of the growing phase was found to be 30–32 mJ m � 2 approximately. The formation of calcite was initiated through the interaction of Ca 2+ ions with the negative end of the –C ¼ O bond as concluded from the quantum mechanical calculations. r 2003 Elsevier Science B.V. All rights reserved.

The influence of Au film thickness and annealing conditions on the VLS-assisted growth of ZnO nanostructures

High temperature evaporation methods, such as the vapor-liquid-solid mechanism, have been exploited for the controlled growth of ZnO nanostructures on various substrates. While Au is the most frequently used catalyst for growing ZnO nanowires, its morphological features on the substrate, which determine the size and shape of the nanostructures grown, have not yet been methodically explored. In the current work, we investigated the details of the thermal dewetting of Au films into nanoparticles on Si substrates. Au films of various thicknesses ranging from 2 to 15 nm were annealed under slow and fast rates at various temperatures and the morphological details of the nanoparticles formed were investigated. The dependence of the mean particle size on the nominal film thickness is in fair agreement with theoretical predictions. The vapor-liquid-solid method was employed to investigate the role of the Au nanoparticles on the growth details of ZnO nanowires. The efficient and high throughput growth of ZnO nanowires, for a given growth time, is realized in cases of thin Au films, i.e. when the thickness is lower than 10 nm. Based on these experimental findings, a two-step mechanism is proposed to account for the growth of ZnO nanorods ending in ultrathin (∼30 nm), micron-long tips.

Novel composites materials from functionalized polymers and silver coated titanium oxide capable for calcium phosphate induction, control of orthopedic biofilm infections: an “in vitro” study

Three copolymers containing the functional groups P=O, S=O and C=O were prepared, and upon the introduction in calcium phosphate aqueous solutions at physiological conditions, “in vitro” were induced the precipitation of calcium phosphate crystals. The investigation of the crystal growth process was done at constant supersaturation. It is suggested that the negative end of the above functional groups acts as the active site for nucleation of the inorganic phase. In order to obtain the copolymer further antimicrobial activity, titania (TiO2) nanocrystals were incorporated in the polymer matrix after silver coverage by UV radiation. The antimicrobial resistance of the composite material (copolymer-titania/Ag) was tested against Staphylococcus epidermidis (SEM), Staphylococcus aureus (SAM), Candida parapsilosis (CAM) and Pseudomonas aeruginosa (PAM), microorganisms, using cut parts of “π-plate” that covered with the above mentioned composite. The antimicrobial effect increased as the size of the nanocrystals TiO2/Ag decreased, the maximum achieved with the third polymer that contained also quartenary ammonium groups.

Stability and physicochemical characterization of novel milk-based oral formulations

PURPOSE The purpose of this work was to assess the colloidal stability of novel milk-based formulations. METHODS Milk-based formulations were prepared in situ by adding into milk alkaline- or ethanolic-drug solutions containing an array of drugs namely; ketoprofen, tolfenamic acid, meloxicam, tenoxicam and nimesulide, mefenamic acid, cyclosporine A, danazol and clopidogrel besylate. The produced formulations were characterized by means of dynamic lightscattering, ζ-potential studies, atomic force microscopy, fluorescence spectroscopy, Raman spectroscopy complemented with ab initio calculations and stability studies. RESULTS The presence of the drugs did not induce significant changes in most cases to the particle size and ζ-potential values of the emulsions pointing to the colloidal stability of these formulations. Raman spectroscopy studies revealed interactions of the drugs and the milk at the intermolecular level. Complementary analysis with ab initio calculations confirmed the experimental observations obtained by Raman spectroscopy. Finally the produced drug containing alkaline/ethanolic solutions exhibited stability over a period of up to 12 months. CONCLUSIONS The current data demonstrate that milk is a promising drug carrier.

Structural Investigation of Vanadium-Sodium Metaphosphate Glasses

Abstract Paper presented a t the NATO A dvanced Study Institute, May 4-1 4 , 2001 (Kas, Turkey) The structure of the glass forming system (V2O5)x -(Na2O • P2O5)(1-x), (x = 0-0.4), has been inves tigated using Raman spectroscopy. The stretching vibrations of various phosphate groups, connected to phosphorus or vanadium atoms, have been assigned. Variation of the composition leads to structural changes where the sodium metaphosphate -P-O-P-chains break and then reconnect with the oxovana-dium units forming a -V-O-P-network structure.

The Effect of Collagen Cross-Linking Procedure on the Material of Intracorneal Ring Segments

Abstract Purpose: To assess the potential impact of corneal crosslinking treatment (365 nm ultraviolet (UV)A irradiation with riboflavin) on the material properties of Intracorneal Rings Segments (ICRS). Materials and methods: Material properties were studied using FT-IR spectroscopy and UV-Vis spectroscopy. Rings were examined: (1) after installation of riboflavin solution, (2) after irradiation with UV-A light and (3) after instillation of riboflavin solution followed by instillation and coeval irradiation. The experiments followed the standard corneal cross-linking (CXL) protocol of corneal crosslinking treatment. Results: After instillation of riboflavin solution, a permanent intense yellow staining of the samples was observed. UV-Vis spectroscopy confirmed that a certain amount of riboflavin solution was absorbed into the samples after CXL procedure. FT-IR spectroscopic analysis showed alterations in the spectra of ICRS mainly at the 2800–3200 cm−1 spectral region [modification in band intensities of CH2 (2925 cm−1) and CH3 (2950 cm−1)]. Conclusions: Our results suggest crosslinking reaction in ICRS material. This should be taken into consideration prior to any CXL treatment of post ICRS-implanted cornea.