Photopolymerization of diacetylenes under hydrostatic pressure

Photopolymerization of diacetylene-bis (toluenesulfonate) (TS-6) under hydrostatic pressure up to 4 kbar has been studied employing timed-resolved absorption spectroscopy of the trimeric reaction intermediate. Formation of the biradical dimer is a non-thermal process occurring at a rate of 10⁷ s^?1 independent of both temperature and pressure. The rate constant for subsequent monomer addition increases exponentially with pressure delineating existence of a linear relationship between height of the energy barrier and reaction distance which is considered to be the key reaction parameter. Measurement of the photopolymerization yield in TS-6, TS-12 and 4-BCMU under pressure in conjunction with statistical considerations confirm (i) that formation of long chains is limited by preformed short chains and (ii) that in TS-6 and TS-12, yet not in 4-BCMU reaction-induced secondary-chain initiation is important.     

Layer-by-layer assembled composite films of side-functionalized poly(3-hexylthiophene) and CdSe nanocrystals: electrochemical, spectroelectrochemical and photovoltaic properties

Regioregular poly(3-hexylthiophene) containing one diaminopyrimidine side group per ten repeat units (P3HT-co-P3(ODAP)HT) can form molecular composites with 1-(6-mercaptohexyl)thymine capped CdSe nanocrystals (CdSe(MHT)) via hydrogen bonds directed molecular recognition. Here we report complementary spectroscopic, electrochemical and spectroelectrochemical investigations of both the functionalized poly(thiophene) and its composite with the nanocrystals, the latter being fabricated using the layer-by-layer (LbL) deposition technique. UV-Vis-NIR and Raman spectroelectrochemical investigations unequivocally show that the onset of the first anodic peak in the cyclic voltammogram of the copolymer can be attributed to the oxidation of the pi-conjugated backbone in the polymer chains. For this reason, it is possible to determine the width and the position of its band gap (corresponding to the pi-pi* transition) by UV-Vis spectroscopy combined with cyclic voltammetry. These studies show that the polymer exhibits a slightly larger band gap with the HOMO level insignificantly lower in energy (by 0.03 eV) as compared to the case of regioregular poly(3-hexylthiophene) of comparable degree of polymerization. Hydrogen bond interactions of the polymer with CdSe(MHT) in the molecular composite result in a hypsochromic shift of the band corresponding to the pi-pi* transition from 504 nm to 488 nm. This can be taken as a spectroscopic manifestation of the conformational changes induced by shortening of the conjugation length. The observed spectral modifications are consistent with electrochemically determined lowering of the polymer HOMO level (from -4.91 eV in the pure polymer to -4.99 eV in the composite). Cyclic voltammetry studies supported by spectroelectrochemistry also show that the redox stability of CdSe(MHT) in the molecular composite with P3HT-co-P3(ODAP)HT is lower than that determined for stearate-capped nanocrystals. Their irreversible oxidation starts at E = +0.7 V vs. Ag/0.1 M Ag(+)i.e. at potentials by ca. 0.3 V lower than the oxidation of stearate stabilized CdSe nanocrystals of the same size. We show that-despite these modifications-the alignment of the HOMO and LUMO levels of the composite components remains appropriate for its use in hybrid solar cells, which is demonstrated by the photovoltaic effect observed for the LbL-processed composite sandwiched between two electrodes.     

Synthesis of icosahedral gold nanocrystals: a thermal process strategy

We demonstrate a one-step thermal process route to the synthesis of icosahedral gold nanocrystals. By regulating the concentrations of poly(vinyl pyrrolidone) (PVP) and HAuCl4 or changing the temperature, we can readily access the shapes of icosahedral nanocrystals with good uniformity. These gold nanostructures, with unique geometrical shapes, might find use in areas that include photonics, optoelectronics, and optical sensing. We also observed that these gold nanocrystals have a strong tendency to be immobilized spontaneously on the glass substrate.     

Pickering emulsions stabilized by cellulose nanocrystals grafted with thermo-responsive polymer brushes

Cellulose nanocrystals (CNCs) from ramie fibers are studied as stabilizers of oil-in-water emulsions. The phase behavior of heptane and water systems is studied, and emulsions stabilized by CNCs are analyzed by using drop sizing (light scattering) and optical, scanning, and freeze-fracture electron microscopies. Water-continuous Pickering emulsions are produced with cellulose nanocrystals (0.05-0.5 wt%) grafted with thermo-responsive poly(NIPAM) brushes (poly(NIPAM)-g-CNCs). They are observed to be stable during the time of observation of 4 months. In contrast, unmodified CNCs are unable to stabilize heptane-in-water emulsions. After emulsification, poly(NIPAM)-g-CNCs are observed to form aligned, layered structures at the oil-water interface. The emulsions stabilized by poly(NIPAM)-g-CNCs break after heating at a temperature above the LCST of poly(NIPAM), which is taken as indication of the temperature responsiveness of the brushes installed on the particles and thus the responsiveness of the Pickering emulsions. This phenomenon is further elucidated via rheological measurements, in which viscosities of the Pickering emulsions increase on approach of the low critical solution temperature of poly(NIPAM). The effect of temperature can be counterbalanced with the addition of salt which is explained by the reduction of electrostatic and steric interactions of poly(NIPAM)-g-CNCs at the oil-water interface.     

Electrochemical synthesis of gold nanocrystals and their 1D and 2D organization

Size-controlled gold nanocrystals were conveniently synthesized through direct electroreduction of bulk AuCl(4)(-) ions in the presence of poly(N-vinylpyrrolidone) (PVP). PVP greatly enhanced the gold particle formation process and also significantly retarded the gold electrodeposition process, allowing the electrochemical synthesis of gold nanocrystals to be carried out in the form of simple electroreduction. This novel electrochemical method may be extended to synthesis of other noble metal nanoparticles with controllable size on a large scale. The PVPK90-protected gold nanocrystals spontaneously self-assembled into nearly ordered 2D close-packed arrays and interesting 1D nanostructures. The aggregation of unstable PVPK17-protected gold nanocrystals resulted in the formation of ultrathin single-crystalline films. PVP plays multifunctional roles in controlling the size and shape of gold nanocrystals and in inducing individual gold nanocrystals to construct 1D nanostructures. The nanoparticle self-assembling technique based on PVP offers a simple, but effective, path to organize individual gold nanoparticles into various 1D and 2D nanostructured materials.     

Energy transfer dynamics of nanocrystal-polymer composites

Steady-state and time-resolved photoluminescence spectroscopy are used to examine the photoluminescent properties of nanocrystal-polymer composites consisting of colloidal PbS nanocrystals blended with poly(2-methoxy-5(2-ethylhexyloxy)-p-phenylene vinylene). Quenching of the emission from the conjugated polymer due to the PbS nanocrystals is observed along with band edge emission from the ligand capped PbS nanocrystals. A decrease in the photoluminescence lifetime of MEH-PPV is also observed in the thin film nanocrystal-polymer composite materials. Photoluminescence excitation spectroscopy of the PbS nanocrystal emission from the composite shows features attributed to MEH-PPV providing evidence of a F?rster transfer process.     

改性纳米羟基磷灰石/PLGA复合材料的制备及生物活性

以低聚乳酸接枝改性的羟基磷灰石纳米粒子(op-HA)和聚丙交酯-乙交酯(PLGA)制备的生物可降解纳米复合材料(op-HA/PLGA)为研究对象, 采用FTIR, TGA, ESEM和EDX分析其接枝反应、接枝率、表面形貌和钙磷沉积情况, 通过在材料膜表面接种兔成骨细胞进行体外培养, 采用荧光染色、NIH Image J图像分析和Real-time PCR综合评价细胞在材料表面的形态、黏附面积比、增殖能力和基因表达水平, 以此评价新型骨修复纳米复合材料op-HA/PLGA的表面性质和生物活性. 研究结果表明, op-HA的表面接枝率为8.3%, 掺入至PLGA后可形成富含钙磷的粗糙表面, 促进成骨细胞的黏附、扩展和增殖, 提高Ⅰ型胶原蛋白(Collagen-Ⅰ)、骨形态蛋白-2(BMP-2)和骨连接蛋白(Osteonectin)的基因表达水平, 提高材料的钙磷沉积能力. op-HA/PLGA具有良好的细胞相容性和成骨活性.     

Synthesis and size control of luminescent ZnSe nanocrystals by a microemulsion-gas contacting technique

A scalable method for controlled synthesis of luminescent compound semiconductor nanocrystals (quantum dots) using microemulsion-gas contacting at room temperature is reported. The technique exploits the dispersed phase of a microemulsion to form numerous identical nanoreactors. ZnSe quantum dots were synthesized by reacting hydrogen selenide gas with diethylzinc dissolved in the heptane nanodroplets of a microemulsion formed by self-assembly of a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) amphiphilic block copolymer in formamide. A single nanocrystal is grown in each nanodroplet, thus allowing good control of particle size by manipulation of the initial diethylzinc concentration in the heptane. The ZnSe nanocrystals exhibit size-dependent luminescence and excellent photostability.     

Chirality of silver nanoparticles synthesized on DNA

Silver nanocrystals grown on a poly(dG)-poly(dC) double stranded DNA scaffold displayed circular dichroism at their surface plasmon excitation band. This chiral plasmon signature was not observed in a control experiment where silver nanocrystals of similar size were produced without the DNA template and adsorbed to the DNA. It is concluded that the DNA templated Ag nanocrystals had a preferred structural handedness.     

纳米CdSe与聚4-乙烯基吡啶盐的复合与表征

用巯基乙酸作稳定剂在水相中合成了CdSe纳米颗粒. 聚4-乙烯基吡啶季铵盐(PVPNI)通过静电作用与CdSe纳米颗粒复合形成了纳米复合材料.该复合材料通过红外光谱数据（IR）、电感耦合等离子发射光谱（ICP-AES）、透射电镜（TEM）等方法进行了表征,并通过紫外可见吸收光谱(UV-Vis)和荧光光谱(PL)对其光学性质进行了研究.结果表明,复合材料的形成,改善了纳米CdSe的分散性,并提高了纳米CdSe的荧光强度.     

Controllable self-assembly of CdTe/poly(N-isopropylacrylamide-acrylic acid) microgels in response to pH stimuli

The self-assembly of hybrid CdTe/poly(N-isopropylacrylamide-acrylic acid) [poly(NIPAM-AAc)] microgels was tunable in response to pH stimuli. The pH-dependent swelling behavior of the polymer microgels played an important role in the self-assembly processes. At pH 3.73, the fractal and dendritic patterns of CdTe/poly(NIPAM-AAc) were fabricated on a large scale, in which the dipole moment of CdTe provided a significant driving force. At pH 11.28, the microgels aggregated and amalgamated to form a porous film and phase separation occurred between the CdTe nanocrystals and poly(NIPAM-AAc). The combination of the physical and chemical properties of inorganic CdTe nanocrystals with those of organic smart polymers provides a new opportunity for controllable self-assembly.     

Size-dependent interaction of the poly(N-vinyl-2-pyrrolidone) capping ligand with Pd nanocrystals

Pd nanocrystals were prepared by the reduction of a H(2)PdCl(4) aqueous solution with C(2)H(4) in the presence of different amounts of poly(N-vinyl-2-pyrrolidone) (PVP). Their average size decreases monotonically as the PVP monomer/Pd molar ratio increases up to 1.0 and then does not vary much at higher PVP monomer/Pd molar ratios. Infrared spectroscopy and X-ray photoelectron spectroscopy results reveal the interesting size-dependent interaction of PVP molecules with Pd nanocrystals. For fine Pd nanocrystals capped with a large number of PVP molecules, each PVP molecule chemisorbs with its oxygen atom in the ring; for large Pd nanocrystals capped by a small number of PVP molecules, each PVP molecule chemisorbs with both the oxygen atom and nitrogen atom in the ring, which obviously affects the structure of chemisorbed PVP molecules and even results in the breaking of involved C-N bonds of some chemisorbed PVP molecules. Charge transfer always occurs from a chemisorbed PVP ligand to Pd nanocrystals. These results provide novel insights into the PVP-metal nanocrystal interaction, which are of great importance in the fundamental understanding of surface-mediated properties of PVP-capped metal nanocrystals.     

Correlated,Dual‐Beam Optical Gating in Coupled Organic–Inorganic Nanostructures

An optical switch with two distinct resonances is formed by combining PbS nanocrystals and the conductive polymer poly[sodium 2‐(2‐ethynyl‐4‐methoxyphenoxy)acetate] (PAE) into a hybrid thin film. Infrared excitation of the nanocrystals invokes charge transfer and consecutive polaron formation in the PAE, which activates the switch for excited‐state absorption at visible frequencies. The optical modulation of the photocurrent response of the switch exhibits highly wavelength‐selective ON/OFF ratios. Transient absorption spectroscopy shows that the polaron formation is correlated with the excited state of the nanocrystals, opening up new perspectives for photonic data processing. Such correlated activated absorption can be exploited to enhance the sensitivity for one optical signal by a second light source of different frequency as part of an optical amplifier or a device with AND logic.     

Correlated,Dual‐Beam Optical Gating in Coupled Organic–Inorganic Nanostructures

An optical switch with two distinct resonances is formed by combining PbS nanocrystals and the conductive polymer poly[sodium 2‐(2‐ethynyl‐4‐methoxyphenoxy)acetate] (PAE) into a hybrid thin film. Infrared excitation of the nanocrystals invokes charge transfer and consecutive polaron formation in the PAE, which activates the switch for excited‐state absorption at visible frequencies. The optical modulation of the photocurrent response of the switch exhibits highly wavelength‐selective ON/OFF ratios. Transient absorption spectroscopy shows that the polaron formation is correlated with the excited state of the nanocrystals, opening up new perspectives for photonic data processing. Such correlated activated absorption can be exploited to enhance the sensitivity for one optical signal by a second light source of different frequency as part of an optical amplifier or a device with AND logic.     

Coordination power adjustment of surface-regulating polymers for shaping gold polyhedral nanocrystals

PVP (poly(vinyl pyrrolidone)) is a common polymer that behaves as a surface-regulating agent that shapes metal nanocrystals in the polyol process. We have used different polymers containing tertiary amide groups, namely PVCL (poly(vinyl caprolactam)) and PDMAm (poly(N,N-dimethyl acrylamide)), for the synthesis of gold polyhedrons, including octahedrons, cuboctahedrons, cubes, and higher polygons, under the present polyol reaction conditions. The basicity and surface coordination power of the polymers are in the order of PVCL, PVP, and PDMAm. A correlation is observed between the coordination power of the polymers and the resulting gold nanocrystal size. Strong coordination and electron donation from the polymer functional groups to the gold surface restrict particle growth rates, which leads to small nanocrystals. The use of PVCL can yield gold polyhedral structures with small sizes, which cannot be achieved in the reactions with PVP. Simultaneous hydrolysis of the amide group in PDMAm leads to carboxylate functionality, which is very useful for generating chemical and bioconjugates through the formation of ester and amide bonds.     

Fabrication of Hierarchical Fe3O4@SiO2@P(4VP‐DVB)@Au Nanostructures and Their Enhanced Catalytic Properties

Hierarchical Fe₃O₄@SiO₂@P(4VP‐DVB)@Au nanostructures were prepared in which the slightly cross‐linked, thin poly(4‐vinylpyridine‐co‐divinylbenzene) (P(4VP‐DVB)) shells were constructed onto Fe₃O₄@SiO₂ nanospheres, followed by in situ embedding of gold nanocrystals homogeneously into the P4VP chains. These slightly cross‐linked chains, easily swollen by the reactants, make the gold nanocrystals accessible to the reactants, and the thin shell (about 15 nm) reduces the diffusion distance of the reactants to the active gold nanocrystals (about 5 nm), thereby enhancing their catalytic activity and utility. At the same time, confinement of gold nanocrystals within the P4VP shells prevents their migration and coagulation during catalytic transformations. Hence the nanocomposites exhibit high activity (up to 4369.5 h^?1 of turnover frequency (TOF)) and controllable magnetic recyclability without any significant loss of gold species after ten runs of catalysis in the reduction of 4‐nitrophenol.     

聚合物主体中纳米CdTe的光致发光与电致发光性质

利用紫外和荧光光谱技术研究了共轭聚合物PPE4+分别在溶液和薄膜中与纳晶CdTe间的能量传递现象。通过静电层层组装技术制备了混杂有纳晶CdTe的PPE4+薄膜发光二极管,并测试了其电致发光性质。结果表明在溶液和薄膜中共轭聚合物PPE4+与纳晶CdTe间均能发生有效的能量转移,而共轭聚合物PPE4+在能量传递过程中起到分子天线的作用。     

One-step synthesis of highly water-soluble magnetite colloidal nanocrystals

A high-temperature solution-phase hydrolysis approach has been developed for the synthesis of colloidal magnetite nanocrystals with well-controlled size and size distribution, high crystallinity, and high water solubility. The synthesis was accomplished by the hydrolysis and reduction of iron(III) cations in diethylene glycol with a rapidly injected solution of sodium hydroxide at an elevated temperature. The high reaction temperature allows for control over size and size distribution and yields highly crystalline products. The superior water solubility is achieved by using a polyelectrolyte, that is, poly(acrylic acid) as the capping agent, the carboxylate groups of which partially bind to the nanocrystal surface and partially extend into the surrounding water. The direct synthesis of water-soluble nanocrystals eliminates the need for additional surface modification steps which are usually required for treating hydrophobic nanocrystals produced in nonpolar solvents through the widely recognized pyrolysis route. The abundant carboxylate groups on the nanocrystal surface allow further modifications, such as bioconjugation, as demonstrated by linking cysteamine to the particle surface. The monodisperse, highly water-soluble, superparamagnetic, and biocompatible magnetite nanocrystals should find immediate important biomedical applications.     

Synthesis of Highly Monodisperse Cu2O Nanocrystals and Their Applications as Hole-Transporting Layers in Solution-Processed Light-Emitting Diodes

The synthesis of phase-pure, narrow-size-distributed and highly stable Cu₂O nanocrystals is reported, which can be processed as hole-transporting layers (HTLs) in solution-processed optoelectronic devices. The synthesis is based on a thermal decomposition process with a ligand protection strategy. The reactivity of precursor can be tuned by simply modulating the concentration of oleylamine in non-coordinated solvent, resulting in effectively controlling the size and size distribution of Cu₂O nanocrystals. Combined with ligand protection strategy of using lithium stearate and moderate reaction temperature of 170 °C, in situ aggregation of Cu₂O nanocrystals could be inhibited, exhibiting excellent stability in hexane for several months. The resulting phase-pure colloidal Cu₂O particles (after ozone-treatment) were applied as HTLs in polymer light-emitting diodes, the performance of which are comparable to that of the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) based devices.     

Poly(lactic acid)-based biocomposites reinforced with modified cellulose nanocrystals

This work investigates reinforcing poly(lactic acid) (PLA) nanocomposites using triazine derivative-grafted cellulose nanocrystals (CNCs). A hydrophobic triazine derivative was synthesized and applied to modify CNCs to improve their thermal stability and diminish the hydrophilicity of the nanoparticles. CNCs before and after modification were used to reinforce PLA nanocomposites by a hot compression process. The results of thermogravimetric analysis indicated that the initial thermal decomposition temperature of modified nanocrystals was improved by approximately 100 °C compared to the original CNCs. That is, the thermal stability of modified cellulose nanocrystals was improved due to the shielding effect of CNCs by a hydrophobic aliphatic amine layer on the surface of the nanoparticles. The results of dynamic contact angle measurements revealed a decrease of hydrophilicity of the modified CNCs. The results from scanning electron microscopy and a UV–Vis spectrophotometer revealed that the compatibility between the modified nanocrystals and the PLA was improved. Finally, the results of tensile tests indicated a significant improvement in terms of breaking strength and elongation at the break point.