[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
[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.
Macromolecular Materials and Engineering 10/2015; DOI:10.1002/mame.201500238 · 2.66 Impact Factor
[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: 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.
[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.
[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.
[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.
[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.
Journal of Photochemistry and Photobiology A Chemistry 05/2015; 303. DOI:10.1016/j.jphotochem.2015.02.013 · 2.50 Impact Factor
[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.
[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.
[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.
[Show abstract][Hide abstract] ABSTRACT: Graphene sheets (GNPs) were functionalized with gold nanoparticles via a spontaneous deposition of gold particles on its surface occurred by chemical reduction of (Au3+). Even after only 1 min of reaction, the reduction of Au3+ into metallic Au0, takes place in evidencing the rapid and spontaneous character of the reduction. The particles, after only 3 min of deposition, have very small diameters, with average centred at 17 nm. The Au–GNP nanofillers were dispersed into UV-curable epoxy resin. Conductivity of the epoxy crosslinked samples containing Au–GNP nanofiller were compared to the values obtained for epoxy nanocomposite containing the same amount of bare graphene; the electrical conductivity was significantly increased by the addition of Au–GNP nanofiller, of about four orders of magnitude. This could be attributed to a charge transfer mechanism, which is strongly enhanced by the presence of gold NPs.
[Show abstract][Hide abstract] ABSTRACT: This work reports the formulation of vinyl ether containing functionalized graphene sheets in order to produce UV-curable conductive inks. The best graphene-surfactant ratio was found to give a stable dispersion of graphene into triethyleneglycol divinyl ether (DVE3) resin, avoiding the presence of large filler aggregates that could clog printing head during ink-jet process. Propylene carbonate was used as solvent to adjust the viscosity of the formulation. The presence of graphene did not significantly hindered the UV-curing process. Crosslinked nanocomposite materials show a decrease of resistivity of seven order of magnitude with respect to the pristine polymeric matrix.
[Show abstract][Hide abstract] ABSTRACT: An organic flexible capacitor was prepared via a multilayer UV-curing process of an acrylic based formulation. The outermost conductive layers were obtained by adding CNTs to PEG-DA resin up to a percolation threshold, found to correspond in between 1 to 2 phr CNTs.The presence of the filler did not significantly influence the photopolymerization rate, while a slight decrease on final acrylic double bond conversion was observed. An increase of Tg values was measured for the films containing CNTs and attributed to an hindering of the polymer chain mobility. A flexible layer was anyway obtained in the presence of 2 phr CNTs, with a Tg value around -25 °C. The three-layer capacitors were electrically characterized, studying impedance module and phase of the system as a function of frequency. Capacitances values are in the range of the shelf standard available discrete components.