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An aromatic photosensitive polyimide is prepared from 3,3`,4,4`-benzophenone tetracarboxylic dianhydride and 4,4`-diaminodiphenyl methane and its structuring ability upon UV-laser exposure is investigated. Surface modification is performed at two laser fluences, i.e. 89 and 244 mJ/cm2, and different number of pulses. The changes of the surface morphology, induced by the employed patterning technique, are examined. According to atomic force microscopy data cone-like structures are formed and their appearance mechanism is analyzed taking into account the laser irradiation conditions. Surface wettability tests reveal an intensification of hydrophobic character, which may be ascribed to the formation of a thin carbon-enriched layer at the polyimide surface. Keywords: polyimide, laser, morphology, wettability

Applications of digital image correlation (DIC) method to material characterisation has been proven to be a powerful tool for deformations and strain analysis and found widespread use and acceptance in the field of experimental mechanics. This paper describes the potential, accuracy and limitations of a commercial DIC system to full-field, real-time characterisation of the coefficient of thermal expansion (CTE) of polymeric materials. The topics such as strain calculation procedure and influence of a small rigid body rotation were theoretically described and experimentally verified. A series of measurements was carried out to determine the CTE polypropylene (PP) and polyvinylchloride (PVC) commercial plastics. To check the feasibility of the method an aluminium sample was initially analysed. The measuring set-up developed includes a simple heating device, thermal sensors and a thermo-camera for real-time temperature measurement and monitoring of the sample and a 3D-DIC measuring system. The results revealed that the DIC can be a reliable tool for thermal deformations measurement especially suitable for polymeric materials with a higher CTE. Keywords: digital image correlation, thermal strains, polymeric materials

Photosensitive polymers based on polysiloxanes substituted with different azo and quaternary ammonium groups were synthesized and characterized. The chemical structure of the synthesized polymers was confirmed using 1H-NMR spectroscopy. The photochromic behaviour was evaluated as a result of the interaction with UV light. The micellar aggregation/disaggregation capacity of the polymers was investigated using fluorescence spectroscopy and dynamic light scattering techniques. All the synthesized amphiphilic polymers are able to generate micelles, the critical concentration of aggregation values being situated in the domain (3-13) x 10-3 g/L. The morphology of the micellar aggregates is fundamentally influenced by the polymer chemical structure. If in the case of azobenzene and azo-5-crwon-15-ether groups it is possible to obtain 35-155 nm diameter individual micelles, for the azo-6-crown-18-ether group, only small aggregates with diameters below 10 nm can be obtained. The micelle’s disaggregation capacity as a consequence of UV irradiation is strongly affected by the hydrophilic/hydrophobic ratio, as well as the chemical structure of the azo groups. Keywords: azobenzene, polysiloxane, photosensitive micelles

By skilful combination between polythiophene backbones and poly(ethylene glycol) (PEG) side chains of different lengths, amphiphilic, fluorescent copolymers having branched architecture of “hairy rods” type were obtained by Suzuki polycondensation. Their structural characterization was performed by 1H-NMR, 13C-NMR and FT-IR spectroscopies and thermal behaviour was followed by differential scanning calorimetry (DSC) and thermogravimetrical analysis (TGA). Photophysical properties in aqueous solutions were evaluated using UV-Vis and fluorescence measurements. The amphiphilic nature of the synthesized polythiophenes and the presence of PEG side chains induced the self - dispersability in water, as well as the formation of fluorescent nanoparticles through self-assembling. The size of the nanoparticles in water was assessed by dynamic light scattering (DLS) and atomic force microscopy (AFM) investigations and the effect of incubation time on three cell lines viability was evaluated, as well. Keywords: polythiophenes, nanoparticles, Suzuki polycondensation, “hairy-rods”, self-assembling

Epoxy resin / carbon nanotubes (CNTs) nanocomposites are nowadays intensively studied in order to produce high performance materials with enhanced properties for specific applications in all activity fields, from electronics to automotive and aeronautics. In order to improve the interactions of CNTs with the polymer matrix, a functionalization of CNTs surface is often required. In this work, functionalized CNTs/epoxy nanocomposites were obtained and investigated by thermogravimetric analysis. Non-covalent functionalized CNTs with three types of surfactants were used. Activation energies of the degradation processes were calculated using Kissinger-Akahira-Sunose isoconversional method. The influence of surfactant type, functionalization mode (covalent or non-covalent) and functionalized CNTs content in composite on the activation energy as a function of the degradation conversion degree was studied. Keywords: thermal degradation, isoconversional method, carbon nanotubes

Necuron is a polyurethane material (PUR) that is used for various applications of industry. The use of these materials in industry increased in recent years because of their good mechanical and machinability properties. Good knowledge of the mechanical behaviour of these materials is highly important therefore this work presents the results of tensile tests carried out on four different types of Necuron. The twenty-eight specimens used were divided in two categories: one without defects and one with defects of two types. Results show that Necuron 1020 is the stiffest material, whereas Necuron 1300 is the strongest. Keywords: tensile testing, necuron, tensile strength, Young’s modulus

Base isolation systems are nowadays largely used to protect the build environment and to avoid loss of life. While the behaviour of natural rubber bearings NRB and lead rubber bearings LRB is well-known, hybrid devices incorporating a NRB and a LRB, due to their complex behaviour, are difficult to be modeled. The authors have developed a theoretical model able to describe with high accuracy the performance during earthquakes of hybrid isolation systems, meantime permitting to determine the equivalent stiffness for all levels of horizontal loads. At the end of the paper numerical simulations give an overview about the possibilities to control the structure response by fitting some parameters of the device. Finally comparison with the behaviour of “classical” devices is performed. Keywords: rubber, neoprene, composites, base isolation, earthquake

The development of resins represented a great step forward in dental technique, the first thermopolymerisable acrylic resins being developed in 1936. Due to their disadvantages, several new materials and their processing technologies, which promise better quality, were introduced on the market, among them diacrylic composite resins. Initially composites were elaborated as esthetic restorative materials, subsequently they developed very much, so nowadays are being used in many various fields of dentistry. Indications for diacrylic composite resins. (DCR) in dental technique include: esthetic veneering for mixed metal-polymeric fixed prosthetic restorations (FPR), unidental or temporary FPR, inlays, onlays, epitheses, repairing damaged porcelain veneers, artificial teeth, manufacturing the base of mobile and removable dentures, repairing and/or re-optimization of the mobile and removable dentures. The aim of this study is to bring into discussion the superior qualities of the the new generation, VITA VM LC (VITA) composite veneering resins. The laboratory steps to be followed in order to obtain a VITA VM LC veneered FPR are the usual ones. After completing the metallic frame, the following step is veneering with VITA VM LC. The VITA VM LC layering concept is oriented after the natural model and is clearly distinguishable from all the other stratification concepts. The natural fluorescence and opalescence reproduction possibility leads to individual results with an aesthetically impressive appearance. A layered restoration performed with VITA VM LC behaves like a natural tooth in different lighting conditions. The excellence in dentistry is often achieved by combining scientific principles with artistic creativity, while choosing the material and technique has a major importance. Keywords: diacrylic composite resin for veneering, VITA VM LC, layering concept, aesthetic results

Dielectric relaxation studies were carried out on unfilled and silica particle filled highly crosslinked PDMS samples, at temperatures above the calorimetric glass transition temperature. Our experiments suggest that the main a relaxation peak is preceded by a pre - a relaxation one, whose characteristics are not dependent in their nature on the presence of the reinforcing silica particles. This suggests that its presence may be characteristic of the high crosslink density PDMS. Keywords: highly crosslinked siloxane elastomers, silica filler, dielectric relaxation in the glass transition region, a-relaxation