Materials Science Forum Vols. 480-481

Abstract: For the modeling of erythrocyte rouleaux we develop an approximation procedure for the dipole moment in short cylinders, which contains the case of ellipsoidal bodies only as a first approximation, but allows to include corrections for short cylinders, more representative for such particles. In dependence on the number of erythrocytes forming an aggregation, i.e. on different but discrete measures of rouleaux lengths, the dielectrophoretic force is calculated and represented against the frequency of the applied a.c. field. Predictions of frequency regions in the range of 107 to 108 Hz are made, where the amount and the direction of dielectrophoresis forces is different for different rouleaux sizes.

Abstract: The aim of this work was the exploration of a potential biocompatible membrane prepared from a modified polyetheretherketone (PEEK-WC). The physico-chemical properties of PEEK-WC were characterised by Differential Scanning Calorimetry and FT-Infrared Spectroscopy. The surface affinity of this membrane to human plasma and proteins such as albumin, fibrinogen and immunoglobulins G was evaluated and compared with that of commercial membranes. The wettability of all investigated membranes was established by water contact angle measurements. PEEK-WC membranes exhibited moderate wettability and low protein adsorption, differently from other commercial membranes such as cellulose acetate membrane. A preferential adsorption of hydrophilic proteins as albumin on the membrane surfaces was observed. Human plasma adsorption on membranes followed the same trend as individual protein solutions.

Abstract: Bovine bone which has been irradiated with the dose bigger than 10 kGy dissolves in water after having been powdered. Bone has been irradiated with the doses of 10, 25, 50, 100, 500, 750 and finally 1000 kGy. The electrical conductivity of solution was measured at the frequency range of 0.1-1 MHz. For the dose range of 10-100 kGy the electrical conductivity and the loss tangent, in the limits of the measurement errors, were dose independent. For the doses higher than 100 kGy both electrical conductivity and loss tangent revealed higher values then for the dose range of 10-100 kGy. Moreover, the relaxation time of the dissolved molecules was assessed as longer than 10-5s.

Abstract: Changes in glass transition and ionic association of PPG/LiClO4 samples with increasing salt concentration have been studied using temperature modulated differential scanning calorimetry (TMDSC)and micro Raman spectroscopy, respectively. PPG, of average molar mass of 3000, was used as host for LiClO4 over the range O:Li = 35 – 4. The analysis of the Raman band, obtained at room temperature, associated with the ν1 symmetric stretching mode of ClO4 - anions, shows the presence of ionic association (ion pair) for electrolytes with salt concentration higher than O:Li = 8. The glass transition changes in the electrolytes were investigated using the differential of heat capacity with respect to temperature [dCp/dT], obtained from TMDSC. The analysis of the dCp/dT signal, by fitting with Gaussian curves, showed that there is a glass transition splitting in samples with concentrations higher than O:Li = 16, which indicates the presence of nanoheterogeneities in these amorphous electrolytes. Raman results pemit to affirm that this nanoheterogeneities were associated mainly with solvent separated ion pairs regions of different concentrations, and not with aggregate of ionic species.

Abstract: We apply a model that connects rheological properties of linear polymer blends with their molecular weight distributions (MWDs). The model is based on the assumption that the relaxation time, ti, of a chain depends on an average molecular weight, M, which determines the effect of the environment where the molecule reptates, and its own molecular weight according to ti = (kE / 0 N G )·M 3.4 - b·Mi b where kE is the constant of proportionality between zero shear viscosity, ho, and weight average molecular weight, Mw, in unimodal polydisperse systems and 0 N G is the plateau modulus. We deduce that the MWD is related to the relaxation spectrum as H(t) = ( 0 N G /b)·M·W(M). Therefore, the MWD is obtained from the relaxation spectrum, which is deduced from the dynamic moduli, G’(w) and G’’(w), constrained by the plateau modulus, the zero shear viscosity and the steady state compliance, 0 e J . The maximum entropy method has been used to solve the integral equation that provides the relaxation spectra from experimental dynamic moduli. The model has been tested in polydimethylsiloxane blends with weight average molecular weight ranging from 94 to 630 kDa and polydispersity from 1.5 to 3.3. Good agreement is found between experimental and calculated MWDs.

Abstract: In this research we study optical absorption and morphology of silver films prepared with a sputtering method. Silver granular films are obtained on a glass substrate for films with thickness smaller than about 60 Å. Superficial silver clusters of around 100 nm in diameter are clearly seen in the atomic force micrographs. The absorption of these samples are characterized by plasmon excitation in the 450-650 nm spectral range, which differs from the known excitation of silver nanoparticles fabricated by different techniques. The optical absorption of silver granular films depend on sputtering conditions like substrate temperature or deposition rate and correlates with the surface morphology.

Abstract: Glass coated microwires with two metallic nucleus compositions Co57Fe 6.1Ni10B15.9Si11 and Fe36,4Co41,7B11,8Si10,1 with 3 different glass coating compositions (Pyrex – 74.5% SiO2, 15% - B2O3, 3%- Na2O, 2%- Al2O3 1.5% -K2O; Nonex – 73% SiO2, 16.5% - B2O3, 6% - PbO 3 %-Na2O, 1.5% -K2O; and F1 – 70.2% SiO2, 27% - B2O3, 0.8 %-Na2O, 2%- LiO2 1% -K2O;) with very similar geometry (metallic nucleus diameter 7 µm, total diameter 19 µm) have been successfully fabricated and studied. Ferich microwires in as-prepared state show rectangular hysteresis loops, which is connected with the strong internal stresses induced by the fabrication process. Co-rich compositions show inclined hysteresis loop with smaller value of coercive field. The coercivity, Hc, of Co-rich microwires is the highest and of Ferich samples is the lowest in the case of Pyrex coated microwires. The Nonex coated microwires are in the intermediate position while the F1 coated Co-rich microwires have the lowest Hc while the Fe-rich samples have the highest Hc. The mechanical tests show that the best tensile strain yield is observed in samples coated by Nonex glass followed by Pyrex and F1. In this way the variation of the glass coating material allows to tailor both magnetic and mechanical properties of glass coated tiny microwires.

Abstract: The ionic conductivity and permittivity of glasses based on ZrF4, BaF2, LaF3, AlF3 and NaF (ZBLAN) or PbF2, InF3, BaF2, AlF3 and LaF3 (PIBAL) are studied. The influence of the glass composition on the glass transition temperature (Tg) and on the crystallization temperature (Tx) is reported. For all ZBLAN glasses the temperature dependencies of the ionic conductivity are close one to another (s500 = 8(2)·10-6 S/cm) and their conduction activation enthalpies are equal to 0.82(1)eV. From the point of view of the ionic conductivity, the best glass compositions are the PIBAL50 (50 m/o PbF2) and PIB45 ( 45 m/o PbF2).

Abstract: The optical and electrical properties of undoped and low doped polycrystalline silicon films deposited by LPCVD technique are analysed. Photothermal deflexion spectroscopy, and electrical conductivity in the temperature range 50- 475 K are used. The effect of low phosphorus doping on the density of defects, electrical parameters and hopping conduction are examined and interpreted in conjunction with the passivation of defects by the introduction of phosphorus atoms. The density of states at the Fermi level is also calculated.

Abstract: A novel hierarchical polygon prismatic nanostructure of wurtzite Zn has been grown on silicon by liquid-solution seed nucleation and vapor-gas growth method. The Zn(ClO4)2 colloidal sol with various concentrations was used as seeds to control the dimension of Zn crystals from the nanometer (30 nm) to micrometer scale (2 µm). Depending on heat-treatment temperature, different morphology was developed. In the temperature range of 200-300oC, a compact polygon prismatic Zn structure was formed. However, in a high temperature range of 300-400oC, polygon prismatic Zn with hollow structure was observed. After oxidation treatment, the ZnO surface layer can be developed on the Zn nanocrystals to form ZnO-Zn core-shell structure as evidenced from PL measurement. These formed ZnO-Zn nano- and micro-crystals can be further used as building blocks to assemble two- or three-dimensional photonic crystals. PACS codes: 81.10.Aj, 64.70.Fx, 64.72.-y