Study of the properties of polymers obtained from vegetable oil derivatives by light scattering techniques

Polymers from oleic acid (principal fatty acid of the olive oil) and methyl oleate were studied by static (SLS) and dynamic (DLS) light scattering in acetone solution. The oleic acid (OA) and methyl oleate (MO) were first epoxidized using a performic acid generated in situ. The epoxidized oleic acid (EOA) and methyl oleate (EMO) were reacted with cis-1,2-cyclohexanedicarboxylic anhydride (CH) as cure agent, triethylamine (TEA) as initiator and small amount of 1,4-butanediol diglycidyl ether (BDGE). According to light scattering results the EMO products without BDGE present low M_W, however the EOA ones are characterized by aggregation and M_W approximately 1.98 × 10⁵ g/mol. The aggregation is evidenced by the presence of two modes in DLS experiments. The dimension of the single particle is approximately R_h = 5 nm and for the aggregates R_h increases until 169 nm. The samples with addition of BDGE in the reaction mixtures for both derivatives (EMO and EOA) result to macromolecular products with M_W higher than 1.71 × 10⁵ g/mol, however no aggregation of this macromolecules is observed. Both products present relatively small dimensions and random coil conformation behavior.     

Physicochemical properties of silver powders obtained by contact precipitation with magnesium

We study the influence of the concentrations of AgNO₃ (0.06–0.32 mole/liter) and NH₄NO₃ (0.1–0.5 mole/liter) in the initial solution and the hydrodynamic conditions for Rev varying within the range 12,950–46,700 on the physicochemical properties of silver powders obtained from secondary solutions of silver (I) nitrate by contact precipitation with magnesium chips within the range 293–323°K. At a temperature of 313°K, for the stoichiometric amount of magnesium chips, turbulization of the medium corresponding to Re _v = 24,200, and the contents of AgNO₃ and NH₄NO₃ in the initial solution equal to 0.06–0.1 mole/liter and 0.25 mole/liter, respectively, we obtain silver powders with a bulk density of 1.09 g/cm³, a specific surface area of 2520 cm²/g (determined according to the gas permeability), and mean particle sizes of 1.0–3.0 μm. Powder particles have perfect geometric shapes with tetragonal and hexagonal symmetry about the axis of growth. The content of Ag in the powder is equal to 99.9 wt.%. It is shown that, by choosing and combining the conditions of contact precipitation, we can get powders with prescribed physicochemical properties.     

用于稠化胶体的高吸水树脂的制备及吸水性能研究

以丙烯酸和丙烯酰胺为单体,N,N-亚甲基双丙烯酰胺为交联剂,过硫酸钾为引发剂,采用水溶液聚合法制备了高吸水树脂。通过正交实验法研究了单体浓度、丙烯酸中和度、引发剂用量和交联剂用量对树脂吸水倍率的影响。最终获得了在蒸馏水中吸水倍率高达3114g/g,在质量分数0.9%NaCl溶液中吸水倍率达157g/g的高吸水树脂,该树脂能够用作稠化胶体的稠化剂来提高胶体的实用性能。     

Study of tribological properties of moulds obtained by stereolithography

Stereolithography (SL) is a process that allows the rapid manufacturing of high-accuracy rapid tools using an ultraviolet laser beam to polymerize a liquid resin, layer-by-layer. In this work, the friction properties of commercial SL resins in contact with several thermoplastics were assessed. Friction experiments were done with plastics overmoulded onto moulding blocks made from SL resins. It was observed that polymers with Hildebrand solubility parameters close to the resins showed adhesion characteristics that were not observed in polymers with values of this parameter further apart.     

Study of tribological properties of moulds obtained by stereolithography

Stereolithography (SL) is a process that allows the rapid manufacturing of high-accuracy rapid tools using an ultraviolet laser beam to polymerize a liquid resin, layer-by-layer. In this work, the friction properties of commercial SL resins in contact with several thermoplastics were assessed. Friction experiments were done with plastics overmoulded onto moulding blocks made from SL resins. It was observed that polymers with Hildebrand solubility parameters close to the resins showed adhesion characteristics that were not observed in polymers with values of this parameter further apart.     

温敏凝胶流变性能动力学研究

应用动态流变实验测定了温敏共聚物的流体特性,分析其在溶胶-凝胶转变过程共聚物溶液随温度变化形成凝胶机理。以室内合成的四元共聚物溶液为基础,采用动态流变实验测定了该共聚物溶液在不同温度、浓度下的剪切模量和损耗模量的变化,确定了凝胶特性,并与试管倒置法比较了凝胶温度。实验结果表明,临界温度为143℃,在一定浓度下(高于接触浓度C*),低于此温度共聚物溶液具有一般粘性流体特性;高于此温度可形成凝胶网络结构;溶液在测试温度(65～240℃)内,其损耗角从56.27°逐渐变为31.04°,溶液体系从粘性流体逐渐到粘弹性流体过渡;说明该溶液在一定浓度下具有温敏特性。     

Structural properties of ultra-fine zirconia powders obtained by precipitation methods

We have investigated various aspects of the stabilization of the tetragonal (t) and cubic (c) forms (metastable at room temperature) with respect to the monoclinic (m) form in ultrafine zirconia powders obtained by calcining amorphous hydrated zirconium oxides at various temperatures. They were prepared by precipitation from ZrOCl₂ at different pH, using either NaOH or NH₄OH solutions. We have clarified the importance of the role of Na⁺ ions in the initial zirconia gel as stabilizers of the cubic form. On the contrary, almost pure tetragonal phase was obtained at moderately low temperatures starting from precursors with a low content of sodium (0.5wt%). By means of an X-ray diffraction (XRD) study and a suitable peak profile fitting procedure (convolutive method for the pattern decomposition followed by a straight-forward Fourier analysis) the amounts of the different crystallographic forms as well their microstructural properties such as crystallite size and lattice disorder (when present) were obtained. The thermal evolution of the systems were followed by both differential thermal analysis (DTA) and XRD, and we studied the martensitic t m transformation obtained by pressing a zirconia powder containing a prevailing content of t form at room temperature. To obtain further microstructural and morphological information on the c m transition, transmission electron microscopy and small angle X-ray scattering techniques were used.     

Electrical properties of new organic composites obtained by mechanochemical synthesis

We present new results on organic semiconductive and metallic composites obtained by direct solid-solid charge-transfer (CT) reaction. By this method, samples of arbitrarily large size are readily achievable. In the present study, we consider composites formed from the reaction between the following pairs of donors and acceptors: TTF and iodine, BEDT-TTF and TCNQ, BEDT-TTF and TCNE, BEDT-TTF and AuI as well as BEDT-TTF and AuI₃. Most of the composites show semiconducting properties only. Two of them, however, (BEDT-TTF)/(AuI) and (BEDT-TTF)₂/(AuI₃), exhibit a metallic behavior.     

Sensor properties of ZnO:Al nanofibres obtained by electrospinning

An electrospinning technology have been developed to obtain zinc oxide nanofibres doped with aluminum. Properties of the obtained nanostructures can be controlled by both the composition of a precursor and subsequent annealing treatment. The gas sensors manufactured with the use of ZnO:Al nanofibres exhibit good response to NO₂ at relatively low operating temperatures. For some samples it was observed that interaction with ambient NO₂ gas causes the change of conductivity from n-type to p-type at higher operating temperatures. This phenomenon was not observed for the samples annealed at higher temperature.     

Chitosan films: crosslinking with EDTA modifies physicochemical and mechanical properties

The present study was aimed to develop chitosan-EDTA films and evaluate their physico-chemical and mechanical properties. The physical properties suggested lowest swelling, volume and volume index of films prepared by employing equal weight of chitosan (CH) and EDTA (1.5% w/v). The CH:EDTA film (1:l, on weight basis) showed minimum contact angle, work of adhesion and high negative spreading coefficient indicating lipophilic behavior of film. Further, the FTIR and DSC analysis suggested maximum crosslinking density in film prepared with equal proportion of CH and EDTA. The mechanical properties explored using texture analyzer revealed increasing the proportions of EDTA rendered the films more flexible and decreased their hardness. Furthermore, in vitro permeation of 5-FU and mesalamine with different solubilities showed minimum permeation across CH–EDTA (1:1) film, indicating high crosslinking density that decreased void space inside the film. Hence, the CH–EDTA conjugate could be considered to be possess great potential for various pharmaceutical applications such as film based delivery systems, controlled and sustained delivery systems etc.     

Magnetic properties of oxide nanopowders obtained by pulsed electron beam evaporation

The magnetic properties of oxide nanopowders obtained by pulsed electron beam evaporation of targets in a low-pressure gas phase have been studied. Using this method, we obtained Zn-ZnO and ZnO nanopowders with the specific magnetization amounting to 2.8 × 10⁻² and 2 G cm³/g, respectively. Significant room-temperature ferromagnetism has been observed for the fist time in a nanopowder of yttria-stabilized zirconia, where the specific magnetization reached ∼6.7 × 10⁻² G cm³/g.     

Characterization of thermoelectric properties of layers obtained by pulsed magnetron sputtering

The pulsed magnetron sputtering technique was applied for the preparation of layers of Bi₂Te₃ and Sb₂Te₃. Target materials were synthesized in evacuated quartz ampoules by melting elemental powders mixed in stoichiometric proportions. The structure and microstructure of targets and prepared films were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. Thermoelectric properties were defined by the Seebeck coefficient and electrical conductivity measurements in the temperature range 320-430 K. The layers were deposited at various powers (0.09-0.20 kW) and currents (0.07-0.16 A) at an argon pressure of about 3.0 Pa. The efficiencies of thermoelectric power obtained for bismuth telluride and antimony telluride were 2-4×10⁻⁴ and 2-6×10⁻³ W K⁻² m⁻¹, respectively. The synthesized materials were used for the fabrication of thermoelectric couples with Bi₂Te₃ as the n-type material and Sb₂Te₃ as the p-type material. The thermocouples were annealed under vacuum to obtain optimum thermoelectric properties. The Seebeck coefficient of thermocouples was evaluated by a Seebeck scanning microprobe [Platzek D, Karpinski G, Stewie C, Muchilo D, Müller E. Proceedings of the second European conference on thermoelectrics, Poland, Cracow, September 15-17, 2004].     

Structure and magnetic properties of nanosized magnetite obtained by glass recrystallization

We present the preparation, structural and magnetic properties of nanosized magnetite obtained by the crystallization of a series of Fe-containing borosilicate glasses. Several compositions with the ratio Fe2O3/SiO2 spanning from 0.37 to 0.67 were investigated as a function of two nucleators Cr2O3 and P2O5, respectively, and modifiers and intermediates (Al2O3 and MgO). M?ssbauer spectroscopy revealed the degree, the type and the location of disorder induced by a specific composition and nucleators. In addition to magnetite, it was also revealed the presence of large amounts of Fe-rich paramagnetic phases. The magnetic response is analysed in relation with the amount of Fe ions which remain dispersed in the glassy matrix as noninteracting (paramagnetic) ions. We discuss the role of the nucleators on the disorder in both tetrahedral and octahedral sites of the magnetite.     

Electrical properties of NiO films obtained by high-temperature oxidation of nickel

Nickel oxide thin films are formed by high-temperature oxidation of nickel foils at 973 K, and are characterized using X-ray diffraction and scanning electron microscopy indicating the formation of a single NiO phase whose thickness grows following a parabolic law. The electrical properties of the formed films are examined by impedance spectroscopy at room temperature; and by measuring direct current (DC) and alternating current (AC) conductivities and dielectric properties at different temperatures. At room temperature, the conductivity is about 4 orders of magnitude higher than that of NiO single crystals. Below 200 K, DC conductivity displays a slight increase with increasing temperature indicating conduction by thermal activation hopping of small polarons. Above 250 K, large polaron conduction associated with holes in the 2p band of O²⁻ with activation energy of about 0.4 eV is observed. Frequency as well as temperature dependencies of the AC conductivity and dielectric constant exhibit trends usually observed in carrier dominated dielectrics.     

Zone-dependent mechanical properties of human articular cartilage obtained by indentation measurements

Emerging 3D printing technology permits innovative approaches to manufacture cartilage scaffolds associated with layer-by-layer mechanical property adaptation. However, information about gradients of mechanical properties in human articular cartilage is limited. In this study, we quantified a zone-dependent change of local elastic modulus of human femoral condyle cartilage by using an instrumented indentation technique. From the cartilage superficial zone towards the calcified layer, a gradient of elastic modulus values between 0.020?±?0.003?MPa and 6.44?±?1.02?MPa was measured. To validate the tissue quality, the histological tissue composition was visualized by glycosaminoglycan and collagen staining. This work aims to introduce a new protocol to investigate the zone-dependent mechanical properties of graded structures, such as human articular cartilage. From this knowledge, better cartilage repair strategies could be tailored in the future.     

Nickel–cobalt alloy nanosheets obtained from reductive hydrothermal-treatment of nickel–cobalt hydroxide carbonate

Nickel–cobalt hydroxide carbonate, a layered material was synthesized by the co-precipitation method using urea as precipitant agent. This anionic layered material with hexagonal structure is constructed from nickel and cobalt ions within the layers and carbonate anions between the layers. Nickel–cobalt alloy with pure cubic phase was obtained by a reductive hydrothermal-treatment of the layered precursor. Powder X-ray diffraction pattern and Fourier transform infrared spectroscopy confirmed the formation of the initial layered material and its metallic alloy product. That is, the nickel–cobalt alloy has really produced via a wet chemical route for the first time. Magnetic measurement revealed that the alloy sample is a soft magnet material.     

Micromechanics and damping properties of composites integrating shear thickening fluids

Damping is an important parameter for vibration control, noise reduction, fatigue endurance or impact resistance of composite materials. In this study, a micromechanical model was used to predict the damping of a composite material containing shear thickening fluids (STFs) at the fibre–matrix interfaces. Predictions of the model and dynamical mechanical analysis results are in concert. The damping of the composites was improved significantly. The dynamic properties exhibited a strong dependence on both frequency and applied external load amplitude. Damping peaks appeared which coincided with the thickening of the STF at the fibre–matrix interface. The location of the peaks depends on the onset of thickening and post-thickening rheological behaviour of the STF. This work shows that a micromechanics approach can be useful for an appropriate choice of microstructural design and properties of STFs in order to control the stiffness and damping behaviour of composites. STFs can be integrated at the microscale of polymer composites to create new materials with load-controlled adaptive dynamic stiffness-damping properties.     

Tribological properties of polymer nanohybrids containing gold nanoparticles obtained by laser ablation

We have studied polystyrene (PS)+Au particles nanohybrids. Approximately spherical gold nanoparticles with the average diameter of 15 nm were obtained by laser ablation in a liquid environment. Thus any chemical residue on the particles was eliminated. Focused ion beam (FIB) milling plus scanning electron microscopy (SEM) observation show that Au particles are fairly well dispersed inside the polymer matrix, better than when PS is simply dissolved in a nanoparticle solution. The Au particles concentration as low as 0.15 wt% results in dramatic changes in tribological properties, namely dynamic friction and pin-on-disk wear. Both wear and dynamic friction results are explained in terms of high brittleness of PS, abrasion of Au particles against a ceramic indenter, and also effects of density of filler particles in the matrix on tribological properties. Effects of varying normal load on friction are small.     

Electrical and transport properties of nickel manganite obtained by Hall effect measurements

Intrinsic resistivity and carrier transport parameters of sintered nickel manganite samples (NTC thermistor grade) were determined using a Hall effect measurement system based on the van der Pauw method. Powder mixtures composed of MnO, NiO and with small amounts of CoO and Fe₂O₃ were free surface energy activated by milling in an ultra fast planetary mill for 5, 15, 30, 45 and 60 min. The powders were uniaxially pressed with 196 MPa into discs and sintered at 1200 °C for 60 min. Full characterization of nickel manganite samples was done using SEM, EDS and XRD analysis. The Hall effect was measured at different temperatures (room temperature, 50, 80, 100 and 120 °C) with an applied field of 0.37 T and also 0.57 T at room temperature. The activation energy E _a (energy of conduction) and the coefficient of temperature sensitivity B _25/80, were calculated from measured resistivity values. The measured mobility, resistivity/conductivity, U-I plots, and Hall coefficients were mutually compared and correlated versus microstructure development and macroscopic parameters such as the powder activation time and ambient temperature.