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Catalytic palladium (Pd) nanoparticles on electrospun copolymers of acrylonitrile and acrylic acid (PAN-AA) mats were produced via reduction of PdCl2 with hydrazine. Fiber mats were electrospun from homogeneous solutions of PAN-AA and PdCl2 in dimethylformamide (DMF). Pd cations were reduced to Pd metals when fiber mats were treated in an aqueous hydrazine solution at room temperature. Pd atoms nucleate and form small crystallites whose sizes were estimated from the peak broadening of X-ray diffraction peaks. Two to four crystallites adhere together and form agglomerates. Agglomerate sizes and fiber diameters were determined by scanning and transmission electron microscopy. Spherical Pd nanoparticles were dispersed homogeneously on the electrospun nanofibers. The effects of copolymer composition and amount of PdCl 2 on particle size were investigated. Pd particle size mainly depends on the amount of acrylic acid functional groups and PdCl2 concentration in the spinning solution. Increasing acrylic acid concentration on polymer chains leads to larger Pd nanoparticles. In addition, Pd particle size becomes larger with increasing PdCl 2 concentration in the spinning solution. Hence, it is possible to tune the number density and the size of metal nanoparticles. The catalytic activity of the Pd nanoparticles in electrospun mats was determined by selective hydrogenation of dehydrolinalool (3,7-dimethyloct-6-ene-1-yne-3-ol, DHL) in toluene at 90°C. Electrospun fibers with Pd particles have 4.5 times higher catalytic activity than the current Pd/Al 2O3 catalyst.

Composites that show visible light transmittance, UV absorption, and moderately high refractive index, based on poly(methyl methacrylate) (PMMA) and zinc oxide (zincite, ZnO) nanoparticles, were prepared in two steps. First, surface-modified ZnO nanoparticles with 22 nm average diameter were nucleated by controlled precipitation via acid-catalyzed esterification of zinc acetate dihydrate with pentan-1-ol. The surface of growing crystalline particles was modified with tert-butylphosphonic acid (tBuPO 3 H 2 ) in situ by monolayer coverage. Particle size and graft density of -PO 3 H 2 on the particle surface were controlled by the amount of surfactant applied to the reaction solution. Second, the surface-modified particles were incorporated into PMMA by in-situ bulk polymerization. Free radical polymerization was carried out in the presence of these particles using AIBN as initiator. Volume fraction (φ) of the particles was varied from 0.10 to 7.76% (0.5 to 30 wt %). Although the particles are homogeneously dispersed in monomer, segregation of the individual particles upon polymerization was observed. Optical constants of the films ca. 2.0 µm including absorption and scattering efficiencies, indices of refraction, and dispersion constants were determined. The absorption coefficient at 350 nm increases linearly with ZnO, obeying Beer's law at low particle contents. However, it levels off toward a value of about 5000 cm -1 and shows a negative deviation at high concentrations because of aggregation of the individual particles. Waveguide propagation loss coefficients of the composite films were examined by prism coupling. A steep increase of the loss coefficient was found with a slope of 52 dB cm -1 vol % -1 as the volume fraction of the particle increases. The refractive index of the composites depends linearly on volume fraction of ZnO and varies from 1.487 to 1.507 (φ ) 7.76%) at 633 nm. The dispersion of refractive index was found to be consistent with Cauchy's formula. IntroductionThe development of polymer-based composites which exhibit various optical functionalities such as high/low refractive index, tailored absorption/emission properties, or strong optical nonlinearities attracts great interest because of the potential optoelectronic applications. 1,2 More specifically, it was pointed out that such composite materials could be applied as transparent substrate or flexible functional layers of optoelectronic devices which require high transparency in the visible range of the optical spectrum. 3 Replacing the conventional substrates made up of inorganic glasses by polymer-based materials could provide a number of advantages, as the polymer composites have milder processing conditions and better impact resistance, can be made flexible, and the optical parameters can be tailored. These composites are typically obtained by the incorporation of functional inorganic particles into a transparent polymer matrix. 3 While the polymeric component provides processability, flexibility, and transparency, the inorg...

Summary: Dispersing surface‐modified zinc oxide nanoparticles (ZnO) in methyl methacrylate (MMA) improves the free radical bulk polymerization process as well as the thermal stability of the formed polymer. Hydroxy groups available on the ZnO surface may induce a degenerative transfer. This suppresses the gel effect, which leads to a better control of the heat evolution during the late stages of polymerization. The formation of chains having vinylidene end groups and head‐to‐head links is suppressed, which shifts the onset of thermal decomposition to the regime where decomposition occurs by random chain scission.Thermal degradation profiles of PMMA and its composite with ZnO at 11 wt.‐%.magnified imageThermal degradation profiles of PMMA and its composite with ZnO at 11 wt.‐%.

A wet-chemical method to produce zinc oxide nanocrystals of monodisperse size distribution (diameter range of 20-80 nm) is presented. The synthesis starts from zinc acetate dihydrate which is converted to ZnO in the presence of 1-pentanol in m-xylene at 130 uC. We report for the first time catalysis of this reaction by p-toluene sulfonic acid monohydrate (p-TSA), which allows a shorter reaction time and improves both the reproducibility of the particle size distribution and the crystallinity of the particles. The reaction can be scaled up to give multigram quantities of product per batch. Particles were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and photoluminesence (PL) spectroscopy. Room temperature PL spectra of ZnO prepared without catalyst exhibit a strong and sharp UV emission band at ca. 385 nm and a weak and very broad green-yellow visible emission centered at ca. 550-560 nm. However, for nanoparticles precipitated in the presence of p-TSA, the UV emission is enhanced by a factor of 4, which can be correlated with the improvement of crystal perfection. A particle formation mechanism is discussed.

Composites of poly(methyl methacrylate) and various nanoscale inorganic particles (zinc oxide, titanium dioxide, zirconium dioxide, silicon dioxide, and aluminum nitride) were prepared by in-situ bulk polymerization using 2,2′-azobis(isobutyronitrile) as initiator. The particles of ZnO, TiO 2 , and ZrO 2 were surfacemodified by alkylphosphonic acids to render them dispersible in the monomer. The effect of these nanoparticles on the free radical polymerization was investigated. Regardless of chemical nature and size, the particles suppress the autoacceleration which would otherwise occur in the bulk free-radical polymerization of methyl methacrylate (MMA). A degenerative chain transfer is proposed to take place between surface-adsorbed water on the particles and propagating chain radicals. This reaction competes with normal termination. Formation of vinylidene chains ends originating from disproportionation is suppressed. In consequence, thermal stability of PMMA produced in the presence of particles is improved. Aggregation of individual particles upon polymerization has been observed and presumably is due to interparticle depletion attraction, even though the particles are individually dispersed in the monomer. Formation of particle clusters is suppressed when a difunctional monomer (e.g., ethylene glycol dimethacrylate) is used as comonomer. The cross-linked medium slows down the diffusion of the particles and therefore interferes with particle aggregation via a depletion mechanism. IntroductionThe combination of inorganic solid particles and polymers is of great interest for numerous existing and potential applications of composite materials in various fields of science and technology. [1][2][3] The general principle of preparation of these composites involves mechanical mixing of the particles with a prefabricated polymer to obtain a so-called compound which can be processed by further conventional techniques for instance extrusion and injection molding. The particles are frequently surface-modified or compounded in the polymer in presence of surfactants in order to enhance the compatibility of the two unlike materials. The increasing popularity of nanoscaled particles which show so-called quantum size effects in terms of optical and electrical behavior has triggered the question whether such particles can be homogeneously dispersed in polymer matrices, thereby giving novel materials by which the unique properties of the inorganic materials can be brought to useful applications. However, nanoscale particles tend to form aggregates, and it is very difficult, if not impossible in many cases, to create mixtures ("compounds") of a given polymer with the desired particles in which the particles are individually and homogeneously dispersed. The nanoparticles rather aggregate and form "clouds" or clusters as a consequence of depletion forces acting between individual particles in the melt or a solution of linear polymers. This mechanism purely driven by entropic forces occurs also when enthalpic interacti...

Black α-CsPbI 3 perovskites are unable to maintain their phase stability under room conditions; hence, the α-CsPbI 3 phase transforms into a thermodynamically stable yellow δ-CsPbI 3 phase within a few days, which has a nonperovskite structure and high band gap for optoelectronic applications. This phase transformation should be prevented or at least retarded to make use of superior properties of α-CsPbI 3 in optoelectronic applications. In this study, Gd 3+ doping was employed with the aim of increasing the stability of α-CsPbI 3 . All doped α-CsPbI 3 nanocrystals with various levels of Gd 3+ , between 5 and 15 mol %, have shown greater phase stability than that of the pure α-CsPbI 3 phase from 5 days up to 11 days under ambient conditions. This prolonged phase stability can be attributed to three potential reasons: increased tolerance factor of the perovskite structure, distorted cubic symmetry, and decreased defect density in nanocrystals. Urbach energy values suggest the reduction of defect density in the doped nanocrystals. Also, use of 10 mol % Gd 3+ as a dopant material increases the photoluminescence quantum yield from 70 to 80% and fluorescence lifetime of α-CsPbI 3 from 47.4 to 64.4 ns. Further, density functional theory calculations are in a good agreement with the experimental results.

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