Preparation and characterization of exfoliated polystyrene/clay nanocomposites using a cationic radical initiator-MMT hybrid

The exfoliated polystyrene (PS)/clay nanocomposites were prepared via in situ polymerization using a cationic radical initiator-intercalated montmorillonite hybrid. The exfoliated structure resulted from the predominant intra-gallery polymerization over the extra-gallery polymerization owing to the anchored radical initiator inside the clay galleries. Several critical properties of the nanocomposites such as the initial thermal degradation temperature, glass transition temperature, storage modulus, Young’s modulus, and tensile strength were estimated and compared with earlier reported literature values. The improvements in such properties were either comparable or much greater than the reported literature values, mainly due to the efficient exfoliation and dispersion of the clay in the PS matrix.     

Hybrid fluorescent polymer-zinc oxide nanoparticles: Improved efficiency for luminescence conversion LED

An incorporation of few weight percentage of n-type zinc oxide (ZnO) on the surface of yellow-emitting fluorescent polymer under mild conditions was demonstrated. Here, a deep level emissive ZnO was selectively deposited on the surface of fluorescent polymer via a simple chemical deposition bath method, at relatively low temperature. The polymer-zinc oxide hybrids, consisting of uniform nanosized spherical fluorescent polymer, having mean diameter ca. ∼500-700 nm were subjected as core molecules capped with different weight ratio of ZnO on the surfaces were prepared successfully. The relative photoluminescence emission efficiency was drastically enhanced as two-fold with just 4 wt% of ZnO incorporation and also more than 10-fold improvement in 50 wt% of ZnO content with respect to pure fluorescent polymer. Bright and efficient white light-emitting devices have been fabricated with these hybrid materials, such as luminescence converter light-emitting diodes (LUCO LEDs), using commercially available GaN LED (460 nm), as a primary pumping source. A device containing 20 wt% of ZnO incorporated hybrid material (2 wt%) exhibits nearly pure white light, having Commission Internationale de I’Eclairage coordinates of (0.30, 0.36) and total luminous flux of 1.80 lm, at an operating voltage of 20 mA. The lifetime measurement data of fabricated device containing polymer-ZnO hybrid materials showed significant improvements over the pure counterpart, due to the “caging effect” of the ZnO shell, which can reduce the self-quenching of the polymer molecules in the core.     

Fabrication and electro chemical properties of poly vinyl alcohol/para toluene sulfonic acid membranes for the applications of DMFC

The novel acid–base membranes composed of para toluene sulfonic acid (pTSA) as an acidic compound, and poly vinyl alcohol (PVA) as a basic compound were fabricated. The morphological and structural properties of the prepared membranes were analyzed by scanning electron microscopy and Infra red spectroscopy. Inclusion of Glutaraldehyde (GLA) and para toluene sulfonic acid (pTSA) promotes the amorphous character of a polymer which causes the free volume for the movement of ions. Thermal and mechanical stability of the acid–base membranes were influenced by the crosslinking agent glutaraldehyde. By the suitable charge carriers of pTSA, hydrophilic channels were promoted for the composite membranes which ensure the ionic conductivity. A high ionic conductivity-methanol permeability selectivity ratio obtained for the prepared PVA/pTSA membrane influences its viable application in direct methanol fuel cells.     

Preparation of polystyrene/montmorillonite nanocomposites using a new radical initiator-montmorillonite hybrid via in situ intercalative polymerization

Polystyrene/montmorillonite (PS/MMT) nanocomposites were prepared by in situ free radical intercalative polymerization, using 1, 3 and 5 wt% of a new cationic radical initiator-MMT hybrid. The corresponding nanocomposites were designated as PS/MMT-1, PS/MMT-3 and PS/MMT-5, respectively. The silicate layers were well exfoliated and randomly dispersed in the PS/MMT-1 and PS/MMT-3, but were less exfoliated in the PS/MMT-5, due to the predominant extra-gallery polymerization over the intra-gallery polymerization. The unique properties of nanocomposites resulted from the strong interactions between the nano-sized silicate layer surfaces and the polymer chains. The onset temperature of thermal degradation, and the glass transition temperature, increased with increasing hybrid content, up to 3 wt%. The molecular weights of the PS in the PS/MMT-1 and PS/MMT-3 were less than those calculated theoretically, due to the predominant intra-gallery polymerization.     

Exfoliated high-impact polystyrene/MMT nanocomposites prepared using anchored cationic radical initiator-MMT hybrid

High-impact polystyrene (HIPS)/montmorillonite (MMT) nanocomposites were prepared via in-situ polymerization of styrene in the presence of polybutadiene, using intercalated cationic radical initiator-MMT hybrid. Incomplete exfoliation of the silicate layers in the HIPS nanocomposites was observed when a bulk polymerization was employed. On the other hand, the silicate layers were efficiently exfoliated in the PS matrix during a solution polymerization, due to the low extra-gallery viscosity, which can facilitate the diffusion of styrene monomers into the clay layers. The resulting exfoliated HIPS/MMT nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, particle size analysis, gel permeation chromatography, and dynamic mechanical analysis. The nanocomposites exhibited significant improvement in thermal and mechanical properties. For example, about 50% improvement in Young’s modulus was achieved with 5 wt% of clay, compared to the unmodified polymer counterpart.     

Growth, morphology and optical properties of tris(8-hydroxyquinoline)aluminum/zinc oxide hybrid nanowires

Hybrid tris(8-hydroxyquinoline)aluminum/zinc oxide (Alq₃/ZnO) nanowires were successfully grown from a one-step solution method at very low temperature. The transformation of amorphous Alq₃ into α-phase crystalline nanowires was achieved by incorporating a certain weight fraction of crystalline ZnO nanomaterials. A growth mechanism was proposed to validate the formation of crystalline Alq₃-ZnO hybrid nanowires with the help of nucleation initiated by the ZnO nanomaterials, followed by Alq₃ molecular aggregation. Effects of temperature on the evolution of morphologies of hybrid nanowires were examined by the field-emission scanning electron microscopy (FESEM). The photoluminescence (PL) spectra of hybrid nanowires showed a significant threefold enhancement in PL intensity, along with a slight blue-shift emission, when compared to the pure Alq₃ molecules, which were attributed due to the incorporation of crystalline ZnO nanomaterials and also the shielding effect of ZnO nanomaterials to avoid the excimer formation between the Alq₃ molecules in the excited state.