Daniel Timpu

New Thermotropc Liquid Crystalline Polyazomethines Containing Luminescent Mesogens

Thermotropic liquid crystalline polyazomethines containing 1,3,4‐oxadiazole chromophors have been synthesized. These polymers are semiflexible liquid crystalline compounds containing luminescent mesogens. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide angle X‐ray diffraction (WAXD) have been used to evaluate their thermal and mesomorphic properties. The target polyazomethines present liquid crystalline behavior with classical calamitic textures, large mesophase range, and high thermal stability. The investigation of the optical properties of the synthesized polymers, in solution and solid state, confirmed a blue fluorescence.

In vitro controlled release of antihypertensive drugs intercalated into unmodified SBA-15 and MgO modified SBA-15 matrices

The use of nanotechnology in medicine and more specifically in drug delivery systems is set to spread rapidly. In order to broaden the range of matrices and implicitly to develop the class of drug delivery systems based on diffusion mechanism, in this study the starting materials, SBA-15 powder matrices, were engineered by MgO modification for antihypertensive drugs intercalation. Captopril and aliskiren were used as drug models. All powders, unmodified and MgO-modified silica matrices, and their corresponding drug-loaded samples were characterized by X-ray diffraction, N(2) adsorption and desorption, FTIR spectroscopy and scanning electron microscopy. The studied drug carriers were tested in the controlled drug release process and the influence of the silica pore morphology and geometry on drug release profiles was extensively studied. In order to analyze the data obtained from the in vitro release studies and to evaluate the kinetic release mechanism, the Korsmeyer and Peppas equation was used. The obtained drug delivery system based on MgO-SBA-15 matrix exhibits exciting structural features and is therefore promising for its use as antihypertensive drug delivery system, having potential therapeutic benefits resulting in safe and effective management of captopril and aliskiren adsorption and in vitro release.

Statistical analysis on morphology development of some semialicyclic polyimides using atomic force microscopy

The morphological features and surface texture parameters of some polyimide films prepared from a flexible and alicyclic dianhydride, in combination with five aromatic diamines, were evaluated by atomic force microscopy (AFM) in order to determine their applicability in electronics. By means of the surface roughness, shape of the surface height distribution, and angular and radial texture, a precise description of the actual surface topographies at the interface with other materials was made. The polyimide structures led to the development of different surface morphologies (from granular to porous and from bumpy to spiky). The relief diversity was described by the entropy of morphology, which had a similar trend with the root mean square roughness, which presents low values, i.e. 0.5–1.8 nm. Three‐dimensional AFM images and the corresponding angular spectra, together with texture aspect ratio and texture direction index (close to 1), indicate that no predominant orientation exists on the investigated surfaces. The redundancy in the morphology was associated with the concept of fractals, the maximum redundancy being achieved for the polyimide with the most complex polymer chain conformation. These results provide useful insights in selecting the polyimide structure, which has the optimal morphology, roughness, orientation, bearing properties, or self‐similarity for microelectronic applications such as: substrate for display backplanes, planar technology, microelectronic packaging, etc. Microsc. Res. Tech. 76:503–513, 2013.

Effect of Cross-Linking Methods on Structure and Properties of Poly(ε-caprolactone) Stabilized Hydrogels Containing Biopolymers

Different dense and porous biodegradable matrices based on solely atelocollagen, or with different atelocollagen and hyaluronic acid derivative ratios, were obtained by varying feeding formulations, cross-linking reaction parameters, and preparative protocols. The compositions and methods for forming hydrogels through a combination of physical and chemical cross-linking processes are provided. The chemical cross-linking was mainly mediated by a synthetic component, a poly(ε-caprolactone) reactive derivative, aiming the development of new hybrid hydrogels with tailored characteristics by an appropriate use of the advantages offered by the included natural and synthetic components and the selection of the preparative procedure. The structure and morphology of the 3D hybrid materials were comparatively investigated by means of Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and environmental scanning electron microscopy (ESEM). FTIR and XRD analysis showed no signs of collagen denaturation during the formation of 3D structures. The influence of various factors, such as the chemical composition of the resulted hydrogels and their morphology, on water uptake and water vapor sorption, mechanical behavior, as well as on in vitro degradation characteristics, was systematically investigated. The experimental results point on the advantage offered by the high and modular physicochemical stability of the ternary hydrogels cross-linked by combined approaches. All newly developed materials show no hemolytic effect, which recommends them for potential biomedical applications.

FTIR investigations of phase transitions in an asymmetric azomethine liquid crystal

The liquid crystalline (LC) behavior of a literature-reported asymmetric azomethine compound (4-[4-(n-butyloxy)-benzylideneimino]-chlorobenzene, Cl.O4) was investigated by using optical polarized light microscopy, differential scanning calorimetry and medium-wide angle X-ray diffraction. FTIR in attenuated total internal reflection configuration was employed to study the microstructural changes occurring during phase transitions of the azomethine. Spectral modifications, associated with molecular conformation rearrangements, allowing the change of the molecular shape from a LC organization to another, have been found. The spectral analysis gave significant evidences for the different phase transitions, thus proving the efficiency of such method for investigating LC materials.

Nanocomposites Based on Aromatic Polyamide-Imide and Magnesium Hydrosilicate Nanotubes

Structure, morphology, and thermal properties of nanocomposites based on thermally stable poly(diphenyloxydamide-N-phenylphtalimide) (PAI) and layered magnesium hydrosilicate nanotubes (NTs) were studied using thermogravimetric analysis, dynamic mechanical analysis, atomic force microscopy, and differential scanning calorimetry. Thermal stability and glass transition temperature of the composites were shown to exceed those of the PAI matrix. Introduction of NT into the polymer matrix appreciably increased the elasticity and deformability of the composite material. The content of NT was also shown to greatly influence the surface morphology of the PAI-NT composites.

Iron–chromium oxide nanoparticles self-assembling into smectic mesophases

Organic-coated iron–chromium oxide (chromite) nanoparticles have been prepared by using the thermal decomposition procedure. For this purpose, the substrate – bimetallic acetate – was treated with oleic acid and dodecylamine as co-ligands in trichloroacetic acid solvent at high temperature (320 °C). The main characteristics and behaviors of the obtained nanoparticles were investigated by combined techniques. The size of the obtained nanoparticles was around 11 nm, as estimated by TEM, WAXD and SAXS, which were in good agreement. The bimetallic nature of the nanoparticles was emphasized by X-ray energy dispersive spectrometry (EDX) and their structure was confirmed by WAXD. The Fourier transform infrared (FTIR) spectrum revealed the bands characteristic to metal oxides as well as to the organic components and confirmed the replacement of the acetate with long chain ligands. The co-existence of the organic coatings and metallic core induced a special behavior that was studied by thermogravimetric analysis, differential scanning calorimetry and polarized optical microscopy. The coated bimetallic nanoparticles proved to be thermostable up to 252 °C and thermotropic showing a highly organized crystalline smectic mesophase (3D plastic mesophase). The organic part alone, in the absence of the inorganic component, did not develop this self-assembly. The results of the magnetic measurements suggest superparamagnetic behavior of the iron–chromium oxide nanoparticles and a weak ferromagnetic behavior.

Morphology and mechanical properties of polymer-inorganic nanocomposite containing triple chain fibrous Na-Mg hydrosilicate

A polymer-inorganic nanocomposite of fibrous Na-Mg triple chain hydrosilicate and polyamidoimide based on 4-chloroformyl-(N-p-chloroformylphenyl)phthalimide and 4,4′-diaminodiphenyl ether has been developed. Morphology and dynamic mechanical properties of the nanocomposite films have been studied. Anisotropy of mechanical properties of the nanocomposite and the pristine polyamidoimide films has been revealed. Introduction of the fibrous filler disrupts the ordered mesomorphic structure of the polymer matrix; its recovery upon heating above the glass transition temperature is possible.

The influence of methoxy side groups and halogen nature on the mesomorphic and optical properties of symmetrical azomethines

ABSTRACT The preparation, characterisation, thermotropic and optical properties of low-molecular azomethines with or without methoxy side group are described in this paper. The azomethine compounds were synthesised by condensation reaction of o-dianisidine/benzidine with para-halogen substituted benzaldehyde. Their properties were analysed by differential scanning calorimetry, thermogravimetry analysis, polarised optical microscopy, X-ray diffraction and optical spectroscopy. The azomethines present liquid crystalline behaviour with large mesophase range and high thermal stability. The compounds without lateral methoxy groups showed smectic A phase, while those with methoxy groups exhibited only nematic phase. The effect of methoxy group and different terminal substituents on the mesomorphic behaviour, molecular and optical properties was estimated in terms of parameters such as molecular polarisability, dipole moment, interdigitation parameter and axial ratio. GRAPHICAL ABSTRACT

Aging behavior of the silicone dielectric elastomers in a simulated marine environment

A series of silicone–barium titanate composites (multiple specimens of each sample), designed as dielectric elastomeric films to be used as active elements in wave energy conversion devices, were immersed in artificial sea water in pseudo-dynamic conditions. While some of specimens were extracted after half a year and subsequently subjected to UV irradiation for 500 h (ASW1/2 + UV procedure), the rest were kept in the saline environment for one year (ASW procedure). The changes that occurred in the structure and morphology as well as in mechanical and dielectric properties were assessed by comparing the obtained results to those of the original samples. Thus, the surface and cross-section morphology was studied by Scanning Electron Microscopy (SEM) having an attached Energy Dispersive X-ray system (EDX), which was used for qualitative elemental analysis and elemental mapping. Changes in surface roughness due to the aging of samples were estimated on the basis of Atomic Force Microscopy (AFM) measurements. The thermal transitions were identified from the Differential Scanning Calorimetry (DSC) data and based on these, the crystallinity degree of the samples was evaluated in each of the three stages. The changes in the structural order were also verified by Wide Angle X-ray Diffraction (WAXD). The tensile toughness, as the amount of energy per volume unit that the material can absorb until failure, was estimated by the area under tensile stress–strain curves. The toughness at 100% elongation was determined on the basis of cyclic stress–strain curves of the original samples as an indirect measure of the energy that the elastic material could release when force that acted on it is removed, like in an energy harvesting system. The aging effect on the viscoelasticity of the samples was evaluated by dynamic mechanical analysis (DMTA), while dielectric spectroscopy was used to estimate the changes in dielectric properties.