[Show abstract][Hide abstract] ABSTRACT: The realization of nanocomposite materials with topologically tailored composition and functional properties represents an important technological challenge for many applications such as optics and electronics. In the last years a great effort was devoted to develop techniques that, by controlling the generation and the distribution of nanoparticles, allow the realization of structured metal/polymer nanocomposites. In this work we present a novel methodology for the realization of patterned silver/polymer nanocomposites generated in a polymeric matrix starting from a single formulation exploiting a fully photoinduced dual wavelength method, maintaining control over size distribution, with a straightforward influence on electronic / plasmonic / photonic properties. Step by step study of the process was carried out, investigating both the polymerization kinetics and the nanoparticles generation. Finally patterning in the polymeric matrix was performed through photolithographic technology and a washing process was developed in order to stabilize the material toward ageing. This technique opens new perspectives in the realization of multifunctional materials and devices exploiting electronic / plasmonic / photonic properties of the embedded nanoparticles and it is envisaged to be further improved by applying region-selective technique.
[Show abstract][Hide abstract] ABSTRACT: This work presents a new method for photocuring epoxy resins using bifunctional curing agents. These curing agents are tertiary amines functionalized with allyl groups. The tertiary amines can cure the epoxy resins by anionic ring opening polymerization of the oxirane groups while the allyl groups react with an added multifunctional thiol by the thiol–ene mechanism. The results showed that the produced polythioethers enhanced the toughness of the obtained polyethers. The kinetics of photopolymerization and the analysis of mechanical properties of the polymers are presented.
No preview · Article · Dec 2015 · Macromolecular Symposia
[Show abstract][Hide abstract] ABSTRACT: Graphene based materials are attracting great attention every day due to their outstanding properties. Widening their potentialities through synergic effects in conjunction with other materials represents an intriguing challenge in order to obtain lighter and multi-functional composites. In this paper, novel self-standing graphene-based paper-like sheets are investigated, obtained via a facile dual step UV-induced process. This method, employing graphene oxide as a starting material, allows the obtaining of polymeric functionalized reduced graphene oxide papers that could be easily handled, featuring improved mechanical and peculiar electrical properties. The mechanical and thermal properties were investigated as well as their electrical response under different stimuli, such as temperature and humidity, showing remarkable changes.
[Show abstract][Hide abstract] ABSTRACT: A new dual-curing, solvent-free process is described for the preparation of tailor-made materials from off-stoichiometric amine-acrylate formulations. The first stage reaction is a self-limiting click aza-Michael addition between multifunctional amine and acrylate monomers with an excess of acrylate groups. The second stage reaction is a photoinduced radical polymerization of the unreacted acrylate groups. By selecting the structure of the monomers and the stoichiometry of the formulations, mechanical and thermal characteristics of the intermediate and final materials can be tuned. The materials obtained after the first curing stage can be gelled or ungelled and loosely or tightly crosslinked at the end of the second curing stage. The methodology used allows to obtain storable and processable intermediate polymers and final networks with optimum properties for different applications. The presence of amines in the reaction medium overcomes the intrinsic oxygen inhibition of acrylate free-radical polymer
Full-text · Article · Oct 2015 · Polymer Chemistry
[Show abstract][Hide abstract] ABSTRACT: A new two-step method involving non-solvent induced phase separation (NIPS) and a UV curing process for the preparation of networked-polysulfone membranes is described. In this approach, first, methacrylated polysulfone macromonomers (PSU-DM)s were prepared by polycondensation followed by end-group esterification. PSU-DMs thin films containing phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO) photoinitiator cast on glass plates were successively subjected to NIPS and UV curing processes to produce the ultrafiltration membranes. The reverse sequence, i.e. first UV-curing followed by NIPS was also applied. Although different double bond conversions were attained, both procedures essentially yielded structurally analogous membranes which were insoluble in DMF, DMSO, and boiling water. UV-curing behavior, structure, thermo-mechanical and morphological properties of the membranes were investigated. Regardless of the preparation sequences, membranes exhibited pure water permeability in the range of tight ultrafiltration membranes.
[Show abstract][Hide abstract] ABSTRACT: A selective modification of the surface properties of UV-cured epoxy films was achieved, with an important enhancement of hydrophobicity and scratch resistance, by dispersion on the UV-curable formulations of fluorinated functionalized silica particles. The photopolymerization process was investigated and the films were fully characterized. Contact angle measurements with water on UV-cured films showed a linear increase of the contact angle of cross-linked films by increasing the functionalized SiO2 content in the photocurable formulation. Also, a consistent and linear improvement of penetration resistance was noted in terms of penetration depth by increasing the fluorinated functionalized silica content.
No preview · Article · Oct 2015 · Macromolecular Materials and Engineering
[Show abstract][Hide abstract] ABSTRACT: Graphene platelets were dispersed into photocurable SU-8 resin. A strong increase of the Tg value as a function of the graphene content was observed and attributed to a mobility hindering effect on the polymeric chains caused by the graphene filler. A significant increase of electrical conductivity is achieved for composites containing functionalized graphene sheets (FGS) between 3 and 4 wt%. The thermal diffusivity of the polymer was observed to increase as a function of filler content in the nanocomposites confirming the conducting nature of the polymeric coating with incorporation of graphene.
No preview · Article · Sep 2015 · Progress in Organic Coatings
[Show abstract][Hide abstract] ABSTRACT: Reactive and non-reactive diblock copolymers based on polyethylene oxide (PEO) and a poly(glycidyl methacrylate) (PGMA, reactive) or polystyrene (non-reactive) block, respectively, are prepared via ATRP and those are incorporated into a cycloaliphatic epoxy matrix. Crosslinking of the matrix is then performed by cationic UV curing, producing modified thermosets. 1H NMR and SEC measurements are carried out and used to analyze the composition, the molar mass and dispersity of the prepared block copolymers. The viscoelastic properties and morphology of the modified epoxy are determined using DMTA and FESEM, respectively. The addition of 4 and 8 wt% of the reactive PEO-b-PGMA block copolymer into epoxy resin has only minor effects on the glass transition temperature, Tg. The reactive homopolymer PGMA significantly increases and the non-reactive block copolymer PEO-b-PS slightly decreases the glass transition temperature of the epoxy matrix. The non-reactive block copolymer PEO-b-PS causes a little decrease in Tg values. The measurement of the critical stress factor, KIC, shows that the fracture toughness of the composite materials is enhanced by inclusion of the non-reactive block copolymer. In contrary, the reactive block copolymer has negative effect on the fracture toughness especially in case of short PEO block. FESEM micrographs studies on the fracture surfaces sustain the microphase separation and the increase in surface roughness in the toughened samples, indicating more energy was dissipated.
No preview · Article · Aug 2015 · Progress in Organic Coatings
[Show abstract][Hide abstract] ABSTRACT: Within the framework of high-temperature polymer fuel cells doped with phosphoric acid, we investigate the replacement of the conventional binder in the catalyst layers by functionalized solid PVDF nanospheres. Aim of this study is to develop and test an innovative binder which might create enhanced electrode porosity and acid distribution. Aqueous suspensions of PVDF nanospheres (d ∼ 200 nm) are obtained by radical emulsion polymerization and are functionalized by Vinyl-Imidazole (VI) groups via in situ γ-radiation. As a consequence the nanospheres can interact with H3PO4 to obtain proton conductivity. Catalyst inks are prepared mixing the nanospheres with commercial Pt/C electrocatalyst powder, solvents and phosphoric acid. Prototype electrodes are deposited by spraying and preliminary fuel cell tests are carried out at 160 °C under dry H2/air. Electrodes with grafted PVDF nanospheres as solid binder are demonstrated and its understanding is in progress. Further improvements are outlined.
No preview · Article · Jul 2015 · Journal of Power Sources
[Show abstract][Hide abstract] ABSTRACT: Magnetite nanocomposites containing Fe3O4 nanoparticles (NPs) retain high interest and long-lasting appeal as multifunctional materials for sensors and actuators with applications to biomedicine as well as to the area of Information and Communication Technologies (ICTs). Most of the current chemical routes to synthesize ferrimagnetic Fe-oxide NPs provide a quite reproducible output and a well-defined chemical composition and structure. The relatively easy synthesis procedure explains the widespread use of both bare and suitably coated Fe3O4 NPs for a variety of applications, especially in the biomedical field.
[Show abstract][Hide abstract] ABSTRACT: Abstract Two types of carbonaceous materials, graphite oxide (GOx) and thermally reduced graphite oxide (TRGO) were tested in the dyes removal from water. Two common synthetic aquatic pollutants, Orange II, an azo dye, and Rhodamine B, a xanthene dye, were selected as probe molecules and their bleaching was evaluated. We observed that the two materials act in a different way when dispersed in aqueous solution: TRGO acts as a good adsorbent material whereas GOx can be used as an efficient photosensitizer. Dye removal is almost complete in the dark in the presence of TRGO and within few minutes a steady-state concentration was achieved. On the contrary, in the case of GOx, adsorption is limited to almost 10-20% for both dyes, but this material is able to induce dyes photodegradation and almost 80% of the residual dyes are abated within 5 h of irradiation under simulated solar light. When the graphene derivatives were dispersed in UV-cured acrylic polymeric films, the reduction of the surface area dropped the adsorption properties of TRGO, whereas the photosensitizer properties of GOx were maintained and the bleaching of the two dyes was achieved.
No preview · Article · Jul 2015 · Journal of Photochemistry and Photobiology A Chemistry
[Show abstract][Hide abstract] ABSTRACT: Photolatent DBN derivatives were shown to be suitable catalysts for the in-situ preparation of novel organic-inorganic hybrid coatings. The formulations are based on organic resins crosslinked by a Michael reaction between acetoacetate modified oligomers and acrylic components, and an inorganic precursor undergoing a base-catalyzed sol–gel reaction. The size of the inorganic nanoparticles can be controlled by the addition of suitable coupling agents, thus allowing the design of hybrid coatings with optimized mechanical properties such as scratch resistance.
[Show abstract][Hide abstract] ABSTRACT: The synthesis of silicon compounds is usually performed by vulcanization at high temperatures in the presence of a platinum catalyst. The activation can also be achieved by UV light irradiation. When a suitable sensitizer is added to the formulation, the reaction can be triggered by lower wavelengths (in the visible spectra). In this way, both energy saving and greater safety are carried out. In the present paper, the reactivity of the trimethyl(methylcyclopentadienyl)-platinum(IV) catalyst (Me-Cp)Pt(Me)3 was investigated under visible light activation (380–515 nm) in the presence of different amount of 2-chlorothioxanthen-9-one (CTX) sensitizer. A proceeding of the curing after the irradiation was also observed leading to the formation of thick samples after short period of irradiation. The properties of the cured material were compared to those obtained by UV light activation.
No preview · Article · May 2015 · Journal of Photochemistry and Photobiology A Chemistry
[Show abstract][Hide abstract] ABSTRACT: The synthesis of silicon compounds is mainly achieved by room temperature or high-temperature vulcanization reaction. Several transition-metal organometallic compounds such as platinum complexes can be used as catalysts to accelerate the thermal reaction. Moreover, these compounds are found to be also efficient for the cross-linking of silicone polymer by UV-activated reaction. In particular, cyclopentadienyl platinum complexes are considered as catalysts that can sustain an extremely high photochemical reaction after UV-light excitation. The reactivity of these catalysts (in particular the trimethyl(methylcyclopentadienyl) (IV) complex (Me-Cp)Pt(Me)3) for the photopolymerization of silicon polymer compounds is evaluated and compared with the most common bis(acetylacetonate)platinum (II) catalyst used for the UV-activated hydrosilation reaction.
[Show abstract][Hide abstract] ABSTRACT: Graphene–epoxy flexible capacitors are obtained by graphene–polymer transfer and bonding via UV-cured epoxy adhesive. Ceramic fillers are dispersed into the epoxy resin with the aim of enhancing the capacitive behavior of the final device. Parallel plate capacitors in which epoxy resin is filled with ceramic nanoparticles demonstrate superior performance, up to two orders of magnitude better than unfilled samples. Zirconia, showing the highest dielectric constant, fails to give a stable output in the whole frequency range, as some competing phenomena occur and reduce the overall polarization of the system. Boehmite appears to be a better choice and gives reasonable performances, better than gibbsite.
No preview · Article · Apr 2015 · Macromolecular Chemistry and Physics
[Show abstract][Hide abstract] ABSTRACT: Interpenetrated hybrid thiol-ene/epoxy network were obtained via UV-induced polymerization. By combining the network structure derived from epoxy curing with that of thiol-ene system we could expect an important toughening effect due to the presence of the polysulfide moieties. It is proposed the use of a penta-allylic triamine curing agent which can react with multifunctional thiols to produce polysulfides in situ, and at the same time has the ability to initiate the anionic polymerization of an epoxy resin. The higher the concentration of polysulfides in the resultant polymer, the better the toughness achieved.
No preview · Article · Jan 2015 · Progress in Organic Coatings
[Show abstract][Hide abstract] ABSTRACT: A straightforward method for immobilizing in-situ generated silver nanoparticles on the surface of a photoactivable isosorbide-derived monomer is developed with the objective to design a functional material having antibacterial properties. The photoinduced thiol-ene mechanism involved in these syntheses is described by the Electron Spin Resonance/Spin Trapping technique. The resulting materials with or without Ag NPs were used as films or as coatings on glass substrate. The surface of the synthesized materials was characterized by X-ray Photoelectron Spectroscopy, scanning electron microscopy, and their thermal and mechanical properties were evaluated by dynamic-mechanical thermal tests, differential scanning calorimetry, thermogravimetric analyses along with pencil hardness, nanoindentation and scratch resistance tests. The photo-induced formation of Ag NPs is also confirmed by UV spectrophotometry. Finally, a primary investigation demonstrates the antibacterial properties of the isosorbide-derived material against Staphylococcus aureus and Escherichia coli, as well as its cytocompatibility toward NIH 3T3 fibroblastic cells.
No preview · Article · Jan 2015 · Biomacromolecules