Publications from 2009

Title Electrical behavior of nematic cells oriented by polypyrrole surface treatment
Author(s) Alexe-Ionescu, AL; Barbero, G; Dascalu, C; Scalerandi, M
Source APPLIED PHYSICS LETTERS 95 (6): Art No. 064101 2009
Abstract We have studied the electrical response of nematic liquid crystal cells with uniform planar alignment imposed by ClO4- doped polypyrrole layers. From the measured electrical current on a resistance in series with the nematic sample when applying a triangular potential with different periods and amplitudes, the diffusion of the ions from the polypyrrole layer into the liquid crystal was evidenced. The sample is described as an insulating liquid containing a distribution of ions depending on the characteristics of the applied external field and also of the polymer layers. A simple model concerning the diffusion of the ions from the aligning doped polypyrrole film inside the liquid crystal is proposed. The agreement between experimental data and numerical results is good.
ISSN 0003-6951
DOI 10.1063/1.3196766

Title Surface energy of a nematic liquid crystal in contact with structured surfaces
Author(s) Alexe-Ionescu, AL; Barbero, G; Komitov, L
Source PHYSICAL REVIEW E 80 (2): Art No. 021701 2009
Abstract A generalization of the functional form of the anchoring energy of a nematic liquid crystal in contact with a structured surface is proposed. The structured surface is represented by side-chain polymer, containing only aliphatic or aliphatic and mesogenic side groups, deposited as a thin alignment film onto a solid substrate. The basic assumption in the model developed in the present work is that the coupling between the polymer side groups and the nematic liquid crystal molecules is responsible for the elastic deformation and compression of the orienting groups taking place in the alignment film. We show that in the limit of small deformations, the surface energy is the same as the one given by the Rapini-Papoular approximation. In this limit, the effective anchoring strength is weak and is due to the elastic deformation of the orienting side groups, which is proportional to the inverse of the length of the aliphatic groups and the length of the linkage group of the mesogens, respectively. In the limit of large deformation, however, the term accounting the film compression is predominant which results in a nonzero torque facilitating the relaxation process of an imposed deformation when the applied electric field is switched off. Good agreement is found between the prediction of our model and the experimental data of the anchoring energy of a nematic liquid crystal aligned by means of Langmuir-Blodgett monolayers of fatty acids as a function of the length of their alkyl chains.
ISSN 1539-3755
DOI 10.1103/PhysRevE.80.021701

Title Surface treatment and bulk density of ions in nematic liquid crystals
Author(s) Alexe-Ionescu, AL; Barbero, G; Ciuchi, F; Mazzulla, A; Scaramuzza, N
Source JOURNAL OF APPLIED PHYSICS 106 (4): Art No. 044508 2009
Abstract The frequency dependence of the electrical impedance of a planar nematic sample in the shape of a slab is investigated. The measurements are performed by means of an external voltage of small amplitude (a few tens of millivolts) in such a manner that the liquid crystal behaves as a linear system from the electrical point of view. In this framework, the nematic orientation induced by the external field is absent because the applied voltage is smaller than the critical one for the transition of Freedericksz for the considered geometry. Our measurements indicate that the real part of the impedance presents a large plateau, finishing at the frequency of Debye. Whereas the imaginary part diverges in the low frequency region, indicating that the electrodes of the cell behave as blocking electrodes. From the value of the plateau of the resistance of the cell and from the frequency of Debye, we can conclude that the surface treatment to orient the nematic liquid crystal has a strong influence on the bulk density of ions. The experimental data relevant to the real and imaginary part of the impedance of the cell have been analyzed with a model based on the equations of continuity for the positive and negative ions and on the equation of Poisson for the actual electrical potential across the sample. By assuming that there is only a type of positive and negative ions and that the electrodes are perfectly blocking, except adsorb ions, we show that the agreement between theoretical predictions and experimental data is good. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3204473]
ISSN 0021-8979
DOI 10.1063/1.3204473

Title Complex Dielectric Constant of a Nematic Liquid Crystal Containing Two Types of Ions: Limit of Validity of the Superposition Principle
Author(s) Alexe-Ionescu, AL; Barbero, G; Lelidis, I
Source JOURNAL OF PHYSICAL CHEMISTRY B 113 (44):14747-14753 2009
Abstract We investigate the influence of two groups of ions on the complex dielectric constant of a nematic liquid crystal limited by perfectly blocking electrodes. The analysis is performed by solving the equations of continuity for the two groups of cations and anions, and the equation of Poisson relating the actual electric field to the net density of charge. We consider a typical experiment of impedance spectroscopy, and evaluate the equivalent resistance and reactance of the cell, in the series representation, versus the frequency of the applied voltage to the cell. We show that the presence of two groups of ions gives rise to two plateaux in the spectrum of the resistance, similar to those related to the ambipolar and free diffusion in the case where there is only one type of ions, but for which the cations and anions have different diffusion coefficients. The correspondence between the usual ambipolar and free diffusion coefficients and those related to the presence of two groups of ions is discussed, The spectra of the real and imaginary parts of the complex dielectric constant are obtained, and their dependence on the bulk densities of the two types of ions is investigated. The nonvalidity of the superposition principle is discussed.
ISSN 1520-6106
DOI 10.1021/jp906479w

Title Models for ionic contribution to the complex dielectric constant of nematic liquid crystals
Author(s) Alexe-Ionescu, AL; Barbero, G; Lelidis, I
Source PHYSICAL REVIEW E 80 (6): Art No. 061203 2009
Abstract We analyze the models that account the ionic contribution to the complex dielectric constant of a nematic liquid crystal. We compare the predictions of the model of [Sawada , Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A 318, 225 (1998)] based on the assumption that the electric field in the liquid coincides with the applied one, with the model of Macdonald where the electric field in the sample is determined in self-consistent manner by solving the equation of Poisson. We show that the model of Sawada , widely used to determine the bulk density of ions and their diffusion coefficient in liquid crystal cells, predicts a thickness dependence of the real and imaginary parts of the dielectric constant different from that predicted by the model of Macdonald. On the contrary, the predictions of the two models coincide for what concerns the frequency dependencies of the two components of the dielectric constant. By considering a typical case, we show that the numerical values of the ionic properties derived by means of the model of Sawada may differ even more than 1 order of magnitude by those predicted by the model of Macdonald. A rescaling procedure allowing to evaluate the bulk density of ions and the ionic diffusion coefficient determined by means of the model of Sawada in agreement with the one of Macdonald is proposed.
ISSN 1539-3755
DOI 10.1103/PhysRevE.80.061203

Title Chromium Doped ZnS Nanostructures: Structural and Optical Characteristics
Author(s) Gogoi, DP; Das, U; Ahmed, GA; Mohanta, D; Choudhury, A; Stanciu, GA
Editor(s) Singh, MR; Lipson, RH
Conference Title International Conference on Transport and Optical Properties of Nanomaterials (ICTOPON 2009)
Conference Date JAN 05-08, 2009
Conference Location Allahabad, INDIA
Abstract Chromium doped ZnS nanoparticles arranged in the form of fractals were fabricated by using inexpensive physico-chemical route. The Cr:ZnS samples were characterized by diffraction and spectroscopic techniques. Unexpected growth of fractals with several micrometer dimensions and of core size 1 mu m (tip to tip) was confirmed through TENT micrographs. At higher magnification, we found that individual fractals consist of spherical nanoparticles of average size < 30 nm. The mechanism leading to such organized structures describing fractal pattern is encountered in this work.
ISSN 0094-243X

Title Detector array incorporated optical scattering instrument for nephelometric measurements on small particles
Author(s) Gogoi, A; Borthakur, LJ; Choudhury, A; Stanciu, GA; Ahmed, GA
Source MEASUREMENT SCIENCE & TECHNOLOGY 20 (9): Art No. 095901 2009
Abstract The design and fabrication of a laser-based laboratory light scattering instrument that uses an array of 16 static Si photodetectors and can be operated at three different incident wavelengths (543.5 nm, 594.5 nm and 632.8 nm) are described. The instrument can measure scattered light signals from 10 degrees to 170 degrees in steps of 1 degrees. The accuracy and the reliability of the setup were verified by conducting measurements on the light scattering properties of polystyrene spheres suspended in water and comparing the results with theoretical Mie calculations. The measurements using this instrument on the light scattering properties of spheroidal rutile (TiO2) particles of average diameter 250 nm are presented.
ISSN 0957-0233
DOI 10.1088/0957-0233/20/9/095901

Title Scanning Laser Microscopy: From Far Field to Near Field
Author(s) Stanciu, GA; Stoichita, C; Stanciu, SG
Conference Title 11th International Conference on Transparent Optical Networks
Conference Date JUN 28-JUL 02, 2009
Conference Location S Miguel, PORTUGAL
Abstract The authors present a short review on different microscopy techniques based on laser scanning microscopy. The corresponding wavelengths of the techniques cover the range from between far field (hundred nanometres) and near field (few nanometres). Our investigations started with a hundred nanometers resolution in the case of laser beam induced current technique and go to nanometre resolution in the case of near field investigations. Different techniques which we used are shortly presented.

Title Cadmium sulphide nanoparticles embedded in polymeric matrices
Author(s) Peretz, S; Sava, B; Elisa, M; Stanciu, G
Abstract Semiconductor nanoparticles represent a very interesting research topic mainly for the optoelectronics applications. The semiconductor particles exhibit properties dependent on the crystallites size, such as the band gap width and the linear optical characteristics (transmission and fluorescence cut-off) besides the non-linear characteristics (refractive index, second and third harmonic generation, two photons absorption, etc). The paper presents the synthesis of CdS nanocrystals and their integration in polymeric matrix. The effect of some polymers with different electrical charges, like polyvinyl alcohol, polyvinyl pyrrolidone, or copolymers maleic anhidride/styrene, maleic anhidride/vynil acetate upon the physico-chemical properties of nanocrystals generated in the aqueous phase was studied. The synthesized nanocrystals were dispersed in polymeric matrix and then were applied on glass support to form films. The properties of the prepared nanoparticles and also the deposited films were investigated by confocal laser scanning microscopy, UV-VIS and fluorescence spectroscopy. In this work we also deal with obtaining of thin films based on colloidal CdS imbedded in potassium silicate-based inorganic polymer. The starting solution was prepared by mixing CdS 10(-4) M aqueous colloidal solution with SSK (potassium silicate solution) aqueous solution (K2O/SiO2=1/5). We prepared several precursor solutions with CdS/SSK=1/1; 2/1; 3/1; 1/2; 1/3 ratios. The films have been obtained by the deposition of the above-mentioned mixture on a silicate glass substrate, by means of a special aluminum device based on “dragging method”. After heat treatment, the films have been characterized by fluorescence spectroscopy, which revealed emission peaks at 450 nm, 465 nm, 500 nm, 525 nm and 540 nm, depending on the size of CdS nanocrystals. The microstructure of the films was proved by TEM (transmission electronic microscopy) analysis which presented the relative homogeneous morphology of the films.
ISSN 1454-4164

Title Feature Based Recognition of Photonic Devices in Images Obtained by Confocal Scanning Laser Microscopy
Author(s) Stanciu, SG; Hristu, R; Boriga, R; Stanciu, G
Conference Title 11th International Conference on Transparent Optical Networks
Conference Date JUN 28-JUL 02, 2009
Conference Location S Miguel, PORTUGAL
Abstract In microscopy the detection, recognition and description of objects contained in images constitute important problems. Recently there have been developed a series of techniques for invariant feature detection/description. These techniques can provide the detection of a set of key points in one image, key points that are invariant to effects like rotation, scale changes, noise, illumination conditions and even view-point. Several comparisons have been conducted [2] for natural images in order to find out which of the techniques provides best performance. In this paper we describe a method for the recognition of images representing photonic quantum ring lasers obtained by scanning laser microscopy. Our feature-based method relies on the scale invariant feature transform technique (SIFT) [1], which at this time is considered to be one of the most robust methods in the detection of invariant features [2]. The recognition of devices represents an important step for developing a registration framework that will consist of several stages : Invariant Feature Detection (with SIFT), Feature Matching, Transform Model Estimation and Image Alignment. Once the images are registered, comparisons over the image content will be easier to be conducted, faster, and more reliable.
Title Polarizabilities of shallow donors in inverse V-shaped quantum wells under laser field
Author(s) Burileanu, LM; Niculescu, EC; Eseanu, N; Radu, A
Abstract The effect of the high-frequency laser field on the subband structure and on polarizabilities of the shallow donors in a GaAs/GaAlAs inverse V-shaped quantum well for different Al concentrations at the structure center is investigated. Calculations are performed in the effective-mass approximation. It is shown that the polarizability decreases with the increasing of the laser intensity and this effect is stronger for high Al concentration at the well center. Our results are in agreement with previous calculations for square and graded quantum wells. (C) 2009 Elsevier B.V. All rights reserved.
ISSN 1386-9477
DOI 10.1016/j.physe.2009.01.008

Title Simultaneous effects of pressure and laser field on donors in GaAs/Ga1-xAlxAs quantum wells
Author(s) Eseanu, N; Niculescu, EC; Burileanu, LM
Abstract Within the framework of effective-mass approximation, using a variational method, the combined effect of the hydrostatic pressure and high-frequency laser field on the binding energy of a hydrogenic impurity in square and parabolic GaAs/Ga1-xAlxAs quantum wells is investigated. Our numerical results show that the effects of the laser field on the electronic properties are more pronounced than those of the pressure ones, and the changes in the binding energy are dependent on the shape of the confinement potential. The variations of the impurity binding energy in intense laser fields can be tuned by the hydrostatic pressure. (C) 2009 Elsevier B.V. All rights reserved.
ISSN 1386-9477
DOI 10.1016/j.physe.2009.04.001

Title Laser effects on the donor states in V-shaped and inverse V-shaped quantum wells
Author(s) Niculescu, EC; Radu, A; Stafe, M
Abstract Laser effects on the electronic states in GaAs/Ga1-xAlxAs V-shaped and inverse V-shaped quantum wells under a static electric field are studied using the transfer matrix method. The dependence of the donor binding energy on the laser field strength and the density of states associated with the impurity is also calculated. It is demonstrated that in inverse V-shaped quantum wells under electric fields, with an asymmetric distribution of the electron density, the position of the binding energy maximum versus the impurity location in the structure can be adjusted by the intensity of the laser field. This effect could be used to tune the electronic levels in quantum wells operating under electric and laser fields without modifying the physical size of the structures. (C) 2009 Elsevier Ltd. All rights reserved.
ISSN 0749-6036
DOI 10.1016/j.spmi.2009.04.001

Author(s) Niculescu, EC; Lupascu, A; Burileanu, LM
Abstract In this paper we study the properties of the quantum-well wires under simultaneous action of hydrostatic pressure and high frequency laser field. Calculation of the optical Stark effect is carried out in the effective mass approximation. Different geometries concerning the size of GaAs/AlGaAs quantum wires as well as the strength of the applied laser field were considered
ISSN 1223-7027

Author(s) Apostol, I; Bojin, D; Maniu, A
Abstract Semiconducting barium titanate materials are used in electronic industry for manufacturing of the positive temperature coefficient thermistors. The properties of these materials are considerable influenced by the technological factors such as sintering temperature and especially by the microstructure and morphology. This paper presents the microstructural investigation of materials samples from two systems (Ba, Sr, Y) TiO3 and (Ba, Pb, Y) TiO3 sintered in the range of temperature 1360 degrees C-1500 degrees C Using a Zeiss – Jena microscope the optical microscopy was performed and the microstructure was studied The medium diameter of the grains and the medium surface of the section of the grains were determined The sintered samples were more studied using JEOL JX4-5 electron microprobe and topography images, composition images, X- radiation images, profile of intensity images were performed The correlation between technological parameter-sintering temperature, microstructure and electrical properties was studied.
ISSN 1582-2214

Author(s) Moldovan, P; Popescu, G; Bojin, D; Constantinescu, D; Pana, M
Abstract An essential problem in automotive industry is to reduce the motor vehicles weight in order to reduce fuel consumption and gases emissions. More and more is estimated that a reduction of weight can be realized by using magnesium and its alloys. By replacing a steel structure with one realized from magnesium alloy it can be obtained a significant weight reduction, nearly 40%. For magnesium and its alloys can be applied three plastic deformation processes: rolling, forging and extrusion. From these processes forging secure to magnesium alloy parts a higher resistance and more close-grained structure. Thus, the paper will present the microstructures of AZ80 and ZK60 magnesium alloys chose for forging parts in MagForge European project. Will also be presented the ways used to improve mechanical characteristics and fatigue resistance.
ISSN 1582-2214

Author(s) Stanica, C; Moldovan, P; Dobra, G; Bojin, D; Dimitriu, S
Editor(s) Bearne, G
Source LIGHT METALS 2009823-826 2009
Conference Title Technical Session on Light Metals 2009 held at the 138th TMS Annual Meeting
Conference Date FEB 15-19, 2009
Conference Location San Francisco, CA
Abstract The AA5083 alloy is one of the most common alloys in the AA5xxx series wrought aluminum alloys. The effect of iron and manganese content on the microstructure and microporosity has been studied by optical microscopy (OM), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis. It was clear underlined that micropores are well connected with iron- and manganese intermetallics, which cause blockage in the interdendritic channels, which hinder feeding and hence promote microporosity of DC cast alloys.
ISSN 0147-0809

Title ICP/MS in evaluation heavy metal influence on the behavior of natural temporary teeth
Author(s) Demetrescu, I; Luca, R; Ionita, D; Bojin, D
Editor(s) Prado, M; Zavaglia, C
Source BIOCERAMICS 21 396-398175-178 2009
Conference Title 21st International Symposium on Ceramics in Medicine
Conference Date OCT 21-24, 2008
Conference Location Buzios, BRAZIL
Abstract The aim of this paper is to evaluate using ICP/MS (inductively coupled plasma mass spectrometry method) the small amount of heavy metal existing in temporary teeth of children from area with high environmental risk regarding heavy metals, and to correlate this amount with the state of degradation of such teeth, taking into account that teeth are biological archive.
ISSN 1013-9826

Title Status and Perspectives for a Slow Positron Beam Facility at the HH-NIPNE Bucharest
Author(s) Straticiuc, M; Craciun, LS; Constantinescu, O; Ghita, LA; Ionescu, C; Racolta, PM; Vasilescu, A; Braic, V; Zoita, C; Kiss, A; Bojin, D
Editor(s) McDaniel, FD; Doyle, BL
Conference Title 20th International Conference on Application of Accelerators in Research and Industry
Conference Date AUG 10-15, 2008
Conference Location Ft Worth, TX
Abstract The development of a positron annihilation spectroscopy laboratory at the HH-NIPNE Bucharest-to be used for material studies and applications was started in the last 10 years. In the framework of a national research project extended over the last 3 years, was designed a low energy positron accelerator, as a high-vacuum dedicated beam line with two options: a 25 mCi (NaCl)-Na-22 source and in line with the NIPNE-cyclotron or a new intense compact cyclotron. The construction of the beam line was planned as a sequence of modules: source-moderator system; magnetical filter for fast positrons in order to select the positrons energies in the range 0.8 – 1 keV; a modular system for focusing, transport and acceleration of monoenergetic positrons in the energy range 0.8 – 50 keV and a CDBS analysis chamber. The moderator proposed – is tungsten as a foil of about 3 mu m prepared at the Optoelectronics Institute were put into a thermal treatment vacuum chamber and bombarded with electrons from a 100W electron gun After the treatment, they were tested for changes of elemental composition of the surface and structure at the Polytechnic University. The structure tests were performed on a DRON 3M diffractometer, with a Co tube (lambda(K alpha)=1.7903 A) – the angular regions studied were around 34 degrees (1 0 0) and 69 degrees (2 0 0). In the present time, the trajectories of the positron are going to be simulated with dedicated software (an ion and electron optics simulator). For the coincidence measurements (CDBS) set-up we used a home-made (NaCl)-Na-22 source, by separation without carrier from a metallic Mg target irradiated with 12 MeV protons and separated by columnar cation exchange. A home-made biparametric system for CDBS measurements will be reported, also.
ISSN 0094-243X

Title Novel fluorescence nanostructured materials obtained by entrapment of an ornamental bush extract in hybrid silica glass
Author(s) Lacatusu, I; Badea, N; Bojin, D; Iosub, S; Meghea, A
Abstract Synthesis of some novel fluorescence nanomaterials loaded with photoactive polyphenols originated from plants with a high spectrum of biological activity, by replacing synthetic chemicals, may open new opportunities for optical and bio-medical applications. This paper presents the synthesis, characterization and fluorescence properties of a new class of materials based on host hybrid matrices obtained through templated sol-gel route, by hydrolysis and co-condensation of tetraorthoethylsilicate with octaisobutyltetracyclo [,11)] octasiloxane-endo-3,7-diol. The aim of paper is focused on the evaluation of the behavior of the fluorescence properties of ornamental bush extract at immobilization in a templated silica matrix and in a silica-silsesquioxane network, using as templates a neutral, non-toxic and biodegradable surfactant from poly(ethyleneglycol) class and a high biocompatible non-surfactant from glucidic class. The proofs of ornamental bush extract entrapment by physical interactions in silica based networks were provided by FT-IR and UV-VIS spectroscopy. The changes of polymer network due to the hydrogen bond interactions between residual Si-OH groups and functional groups of organic molecules from extract were evidenced by shifts of specific vibrations. In UV-VIS-NIR domain, the chromophore groups from ornamental bush extract were also evidenced by similar small shifts. As a result of ornamental bush extract entrapment, in all the immobilized samples the fluorescence intensity was more than 10 times amplified in samples templated with poly(ethylenglycol) surfactant) and of about 5 times in samples with glucidic template due to the physical adsorption of polyphenolic molecules from extract, excellent synergistic optical properties of SiO2 and silsesquioxane compound and also due to a favorable conformational arrangement. The size of synthesized polymeric materials, estimated by dynamic light scattering technique showed main diameters less then 1.4 mu m, namely 1,060 and 211 nm-for samples with d-glucose template and 1,330 and 531 nm-for samples with poly(ethyleneglycol) template, respectively, with a narrow size distribution and a polidispersity varying between 0.022 and 0.426. These results are in good accordance with TEM images that evidenced the presence of some polymeric aggregates which contain the vegetal extract immobilized inside hybrid SiO2-Sq polymeric network of about hundred nanometers size. This study bring new contributions to the development of the sol-gel procedure by entrapment of a complex vegetable mixture in polymeric matrices as integral component of silica and hybrid silica-silsesquioxane networks which leads to a significant enhancement of the functional properties of the final material, thus diversifying the potential applications of organic doped sol-gel glasses.
ISSN 0928-0707
DOI 10.1007/s10971-009-1925-2

Title Role of silsesquioxane compounds used as ‘building blocks’ in sol-gel nanoencapsulation of retinyl palmitate
Author(s) Lacatusu, I; Nita, R; Badea, N; Bojin, D; Meghea, A
Conference Title 2nd International Conference on Functional Materials and Devices
Conference Date JUN 16-19, 2008
Conference Location Kuala Lumpur, MALAYSIA
Abstract The aim of paper is focused on development of novel alternative solutions in order to realise a combination of sensitive molecules with rigid support materials. In this context, a new class of silica precursors based on bridge bonded silsesquioxane organised into periodic mesoporous architecture is suitable for this purpose. A silsesquioxane incompletely condensed (dimethylvinylsilyloxy)-heptacyclo-pentyltricycloheptasiloxanediol) has been selected for sol-gel bioentrapment of retinyl palmitate, in an approach based on high biocompatibility and mild sol-gel encapsulation conditions which enables the reproducible and efficient confinement of retinyl palmitate inside silica. For entrapping of retinyl palmitate within cage structure a templating agent was used, n-dodecyl-beta-D-maltoside. The process used for retinyl palmitate encapsulation in silsesquioxane matrix consisted in two main steps: the first step was the synthesis of glucosidal template silica materials, and the second was the encapsulation of retinyl palmitate into silica silsesquioxane network.
ISSN 1432-8917
DOI 10.1179/143307509X440677

Title Synthesis of high fluorescent silica hybrid materials by immobilization of orange peel extract in silica-silsesquioxane matrix
Author(s) Lacatusu, I; Badea, N; Nita, R; Giurginca, M; Bojin, D; Iosub, I; Meghea, A
Abstract Sol-gel chemistry can be easily modified to the changing needs of society to produce fine-tuned sol-gel nanostructured materials for relevant applications. In this context, there is an increasing need for natural and versatile raw materials as well as biocompatible compounds that could be extensively used as biomarkers for bioimaging in diagnosis or therapy. Silica-based materials are widely used in the field of biomedicine due to their chemical inertness and biocompatibility. In the present paper, orange peel extract was immobilized inside inorganic silica and hybrid silica-silsesquioxane polymeric networks. Silica and organo-modified silica matrices were synthesized through a templated sol-gel route of TEOS and an organosilsesquioxane (octaisobutyltetracyclo[,11)] octasiloxane-endo-3,7-diol), with D-glucose as template, and for comparison a non-ionic surfactant (tetraethylene glycol mono-hexadecyl ether) was also used. The bioactive properties of the molecules from orange peel extract were preserved after immobilization in both silica and silica-silsesquioxane networks. Moreover, the fluorescence properties were amplified by 10-20 times more than the native orange peel extract. The structural properties of the final materials have been studied by FT-IR, UV-Vis-NIR, and fluorescence spectroscopy. Dynamic light scattering measurements and transmission electron microscopy were used to estimate the size and morphology of the hybrid materials with orange peel extract immobilized in silica networks. Copyright (C) 2009 John Wiley & Sons, Ltd.
ISSN 0894-3230
DOI 10.1002/poc.1559

Title A new approach in evaluation surface properties of natural temporary teeth from high polluted area
Author(s) Prodana, M; Luca, R; Miculescu, F; Bojin, D
Editor(s) Ionita, D
Conference Title Workshop on Electrochemistry and Physical Chemical Methods in Serving Materials for Sustainable Development
Conference Date SEP 09-12, 2009
Conference Location Sinaia, ROMANIA
Abstract The aim of this paper is to evaluate surface properties of natural temporary teeth from high polluted area by dynamics of balance hydrophil hydrophob in connection with surface analysis type atomic force microscopy (AFM). All the data were discussed in relation with the state of degradation of such teeth, taking into account that teeth are biological archive.
ISSN 1013-9826

Title Scanning Electronic Microscopy in Supporting Electrochemical Deposition and Characterization of Hybrid Polymeric Composite
Author(s) Piru, C; Mindroiu, M; Stancu, R; Bojin, D; Demetrescu, I
Editor(s) Ionita, D
Conference Title Workshop on Electrochemistry and Physical Chemical Methods in Serving Materials for Sustainable Development
Conference Date SEP 09-12, 2009
Conference Location Sinaia, ROMANIA
Abstract In this paper both electrochemical and surface analysis technique, were performed in order to elaborate and investigate hybrid polymeric composite materials based on polypyrrole (PPy). SEM micrographs of PPy films obtained on zinc chromate electrode presented a cauliflower-like structure. The anticorrosive properties of composite coatings based on polypyrrole were improved using a pre-treatment with chromium salts on the zinc-coated steel surfaces.
ISSN 1013-9826
Title Thickness dependence of the anchoring strength in dye-doped nematic liquid crystal cells
Author(s) Dascalu, C; Ionescu, AT
Abstract Anchoring properties of polymer coated glass surfaces in nematic liquid crystal cells should not depend on the thickness of the cell. Nevertheless, in the case of cells filled with dye-doped nematic liquid crystals the anchoring energy decreases when the cell thickness increases. This experimental fact was explained by considering that adsorption of dye molecules onto the polymer coatings plays the role of defects on the aligning surfaces. A theoretical model, in terms of free energy formalism, was suggested that explains well the experimental results.
ISSN 1454-4164

Author(s) Dascalu, C; Atasiei, R; Raicopol, MD
Abstract Electric conduction measurements were performed to estimate ionic charge densities and Debye screening length within a nematic liquid crystal aligned with conductive polymers. The study has been carried out on standard sandwich symmetric cells filled with nematic liquid crystal 5CB. Planar orientation was induced using thin films of polypyrrole doped with ions having different molecular sizes and geometries. BY assuming that, in a sample, the ions are identical except for the sign of the electrical charge, the ion densities and the Debye lengths in thermodynamical equilibrium for each cell were determined. Decreasing values of Debye lengths for increasing thickness of same alignment conductive polymer films are revealed for long enough periods of triangular applied voltages.
ISSN 1223-7027