Polymer/Laponite Composite Latexes: Particle Morphology,Film Microstructure,and Properties

Transparent film materials with excellent mechanical and thermal properties were elaborated by drying a latex suspension of armored polymer/Laponite composite particles. Low‐temperature TEM observation of ultrathin cross‐sections of the films indicated a unique network morphology characterized by a “honeycomb” distribution of the Laponite platelets remindful of the original particles morphology.

     

Controlled,micro‐scale film formation of waterborne dispersions

The film formation on a micro‐scale of latex material is described. Waterborne polymer dispersions dried below their Tg are treated by laser or direct heat treatment by means of a tip (diameter 5 µ m) of a micro thermal analysis apparatus (µ ‐TA). Both methods give a linewidth, line thickness and dot‐sizes in the micron range. The layer thickness decreases during fusion of the particles because of the loss of voids during film formation. Non treated areas can be washed away selectively. Laser treatment gives a more smooth surface than direct thermal treatment with a µ‐TA tip. Copyright © 2001 John Wiley & Sons, Ltd.     

Fullerene Derivatives Embedded in Hybrid Sol-Gel Glasses: Nonlinear Optical Properties and Optical Limiting Performances

Hybrid organic-inorganic materials are investigated as suitable materials for inclusion of fullerene derivatives and for fabrication of laser protection devices. A specific synthesis has been developed in order to optimize non-linear optical performances of fullerene derivatives. 3-glicydoxypropyltrymethoxysilane has been used as an inorganic and organic network former to obtain the host material. The sol-gel synthesis consists of the hydrolysis and condensation in acidic conditions of the inorganic network. Epoxy polymerization has been achieved by using zirconium or BF₃ alkoxides precursors. Bulk and multilayer materials doped with a fullerene derivative have been fabricated. They show good optical requirements: high fullerenes concentration, high microstructural homogeneity, high laser damage threshold and high optical limiting efficiency. Optical limiting (OL) mechanisms have been investigated. The most effective in the sol-gel materials is the reverse saturable absorption (RSA) one. However, different mechanisms, like non-linear (NL) scattering and NL refraction contribute to a different extent. Open- and closed-aperture OL and z-scan measurements on sol-gel samples show the contribution of NL scattering and NL refraction at 690 nm. Laser damage threshold has been characterized as a function of the structure of the samples and of the optical configurations (f/66 and f/5).     

Polyimide-Silica Hybrids: Spectroscopy,Morphology and Mechanical Properties

Polyimide/silica hybrids were prepared by a sol-gel process and were evaluated in terms of curing behaviour, morphology and mechanical properties. The spectroscopic examination showed that the presence of the inorganic phase accelerates the imidization of the polyamic acid. Two types of morphology for the silica phase were obtained by tailoring the composition of the precursor solution mixture. The mechanical properties were found to be strongly dependent on the system morphology. The largest increase in rigidity and strength properties were achieved when the two phases were co-continuous.     

Strong,Thermally Superinsulating Biopolymer–Silica Aerogel Hybrids by Cogelation of Silicic Acid with Pectin

Silica aerogels are excellent thermal insulators, but their brittle nature has prevented widespread application. To overcome these mechanical limitations, silica–biopolymer hybrids are a promising alternative. A one‐pot process to monolithic, superinsulating pectin–silica hybrid aerogels is presented. Their structural and physical properties can be tuned by adjusting the gelation pH and pectin concentration. Hybrid aerogels made at pH 1.5 exhibit minimal dust release and vastly improved mechanical properties while remaining excellent thermal insulators. The change in the mechanical properties is directly linked to the observed “neck‐free” nanoscale network structure with thicker struts. Such a design is superior to “neck‐limited”, classical inorganic aerogels. This new class of materials opens up new perspectives for novel silica–biopolymer nanocomposite aerogels.     

On‐Surface Synthesis and Characterization of Triply Fused Porphyrin–Graphene Nanoribbon Hybrids

On‐surface synthesis offers a versatile approach to prepare novel carbon‐based nanostructures that cannot be obtained by conventional solution chemistry. Graphene nanoribbons (GNRs) have potential for a variety of applications. A key issue for their application in molecular electronics is in the fine‐tuning of their electronic properties through structural modifications, such as heteroatom doping or the incorporation of non‐benzenoid rings. In this context, the covalent fusion of GNRs and porphyrins (Pors) is a highly appealing strategy. Herein we present the selective on‐surface synthesis of a Por–GNR hybrid, which consists of two Pors connected by a short GNR segment. The atomically precise structure of the Por–GNR hybrid has been characterized by bond‐resolved scanning tunneling microscopy (STM) and noncontact atomic force microscopy (nc‐AFM). The electronic properties have been investigated by scanning tunneling spectroscopy (STS), in combination with DFT calculations, which reveals a low electronic gap of 0.4 eV.     

Film formation of polymeric emulsions: Structure set-up and the pinhole effect characterized by microscopic techniques

Drying of emulsions of special polymeric core-shell latexes results in structured films and coatings with advantageous material properties. Here, we focus on so-called “container particles”, consisting of a low viscosity core with a low glass transition (poly(2-ethylhexyl methacrylate), PEtHMA), covered by a thin shell of a cross-linked rubber (poly(n-butyl acrylate), PBA). These particles can be regarded as model emulsions of reactive polymeric oils with a very high colloidal stability. The film formation of these latexes was studied by atomic force microscopy (AFM) in the tapping mode as well as by transmission electron microscopy (TEM). It is shown that the films stay nanostructured after the drying process, i. e. they exhibit both a controlled topography as well as a network superstructure originating from the characteristics of the original dispersions.

TEM allows to detect the whereabouts of the polar stabilizer. Both continous surfactant films as well as inverted micelles are found. A geometrically induced demixing phenomenon is found which enriches the polar components and might be the molecular reason for the so-called pinhole-effect, the failure of water-born coatings in contact with water.     

Silicon Nanocrystals and Silicon‐Polymer Hybrids: Synthesis,Surface Engineering,and Applications

Silicon nanocrystals (Si‐NCs) are emerging as an attractive class of quantum dots owing to the natural abundance of silicon in the Earth's crust, their low toxicity compared to many Group II–VI and III–V based quantum dots, compatibility with the existing semiconductor industry infrastructure, and their unique optoelectronic properties. Despite these favorable qualities, Si‐NCs have not received the same attention as Group II–VI and III–V quantum dots, because of their lower emission quantum yields, difficulties associated with synthesizing monodisperse particles, and oxidative instability. Recent advancements indicate the surface chemistry of Si‐NCs plays a key role in determining many of their properties. This Review summarizes new reports related to engineering Si‐NC surfaces, synthesis of Si‐NC/polymer hybrids, and their applications in sensing, diodes, catalysis, and batteries.     

Alkaline–Acid Zn–H2O Fuel Cell for the Simultaneous Generation of Hydrogen and Electricity

An alkaline–acid Zn–H₂O fuel cell is proposed for the simultaneous generation of electricity with an open circuit voltage of about 1.25 V and production of H₂ with almost 100 % Faradic efficiency. We demonstrate that, as a result of harvesting energy from both electrochemical neutralization and electrochemical Zn oxidation, the as‐developed hybrid cell can deliver a power density of up to 80 mW cm^?2 and an energy density of 934 Wh kg^?1 and maintain long‐term stability for H₂ production with an output voltage of 1.16 V at a current density of 10 mA cm^?2.     

Covalent Functionalization of Graphene by Nucleophilic Addition Reaction: Synthesis and Optical‐Limiting Properties

Covalent functionalization of reduced graphene oxide (rGO) was performed by using conjugated polymers with different monomers through nucleophilic addition of nitrogen anions to rGO. Three conjugated polymers containing tetraphenylethylene, carbazole, and phenyl groups were used, and as a result of π–π interactions and the “polymer‐wrapping” effect, the dispersion stability of rGO was improved. Even if the reaction site in the polymers was the same, there were great differences in the reactivities of the polymers, the dispersion stabilities of the resultant composites, and also the optical limiting (OL) performances of the resultant composites. The differences may be attributed to the π‐conjugated structure and steric hindrance of the moiety in the polymer skeleton, which has scarcely been reported. Besides, the resultant rGO‐P1 and rGO‐P3 materials both showed excellent OL responses, even at 4 μJ. This behavior should enable their potential application in photonic and optoelectronic devices to protect human eyes or optical sensors from damage by intense laser irradiation.     

Formation and Thermal Stability of Gold–Silica Nanohybrids: Insight into the Mechanism and Morphology by Electron Tomography

Gold–silica hybrids are appealing in different fields of applications like catalysis, sensorics, drug delivery, and biotechnology. In most cases, the morphology and distribution of the heterounits play significant roles in their functional behavior. Methods of synthesizing these hybrids, with variable ordering of the heterounits, are replete; however, a complete characterization in three dimensions could not be achieved yet. A simple route to the synthesis of Au‐decorated SiO₂ spheres is demonstrated and a study on the 3D ordering of the heterounits by scanning transmission electron microscopy (STEM) tomography is presented—at the final stage, intermediate stages of formation, and after heating the hybrid. The final hybrid evolves from a soft self‐assembled structure of Au nanoparticles. The hybrid shows good thermal stability up to 400 °C, beyond which the Au particles start migrating inside the SiO₂ matrix. This study provides an insight in the formation mechanism and thermal stability of the structures which are crucial factors for designing and applying such hybrids in fields of catalysis and biotechnology. As the method is general, it can be applied to make similar hybrids based on SiO₂ by tuning the reaction chemistry as needed.     

Benzofuran–isatin Hybrids: Design,Synthesis, and In Vitro Anti‐cancer Activities

A series of novel benzofuran–isatin hybrids 6a – s tethered through propylene and butylene were designed, synthesized, and evaluated for their in vitro anti‐cancer activities against HepG2 (liver carcinoma), Hela (cervical cancer), A549 (lung adenocarcinoma), DU145 (prostatic cancer), SKOV3 (ovarian carcinoma), MCF‐7 (breast cancer), and drug‐resistant MCF‐7/DOX (doxorubicin‐resistant MCF‐7) human cancer cell lines. The majority of the synthesized hybrids displayed weak to moderate in vitro activities against the tested seven cancer cell lines, but the enriched structure–activity relationship may pave the way for further optimization.     

Inorganic–Organic Heteropolyacid–Gold(I) Hybrids: Structures and Catalytic Applications

Gold(I)‐polyoxometalate hybrid complexes 1 – 4 ([PPh₃AuMeCN]_xH_4?xSiW₁₂O₄₀, x=1–4) were synthesized and characterized. The structure of the primary gold(I)–polyoxometalate 1 (x=1) was fully ascertained by XRD, FTIR, ³¹P and ²⁹Si magic‐angle spinning (MAS) NMR, mass spectroscopy, and SEM–energy dispersive X‐ray spectroscopy (EDX) techniques. Moreover, this complex exhibited better catalytic activity and selectivity compared with standard, homogeneous, gold catalysts in the new rearrangement of propargylic gem‐diesters.     

Polyimide–silica hybrid coatings: morphological,mechanical, and thermal investigations

In this study, polyimide–silica (PI–silica) based hybrid coating compositions were prepared from tetraethoxysilane (TEOS), γ‐glycidyloxypropyl trimethoxy silane (GOTMS), and polyamic acid (PAA) via a combination of sol–gel and thermal imidization techniques. PAA was synthesized from 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) and 3,3'‐Diaminodiphenyl sulfone (DDS) in N‐Methyl‐2‐pyrrolidone (NMP). The silica content in the hybrid coatings was varied from 0 to 20 wt%. The structural characterization of the hybrid coatings was performed using FTIR and ²⁹Si‐NMR spectroscopies. Results from both pendulum hardness and micro indentation test show that the hardness of hybrid coatings improves with the increase in silica content. The tensile tests also demonstrated that the mechanical properties at low silica content are rather striking. Their surface morphologies were characterized by scanning electron microscopy (SEM). SEM studies revealed that inorganic particles were distributed homogenously through the PI matrix. It was also found that, incorporation of the silica domains increased the thermal stability of the hybrid coatings. Copyright © 2007 John Wiley & Sons, Ltd.     

Peptide‐Coated Silver Nanoparticles: Synthesis,Surface Chemistry,and pH‐Triggered,Reversible Assembly into Particle Assemblies

The degree of aggregation of silver nanoparticles can be controlled via a pH sensitive peptide coating (see figure). As the peptide not only controls the colloidal properties, but also influences the crystal structure of the individual nanoparticles, peptide/silver particle hybrid materials can be viewed as flexible and simple building blocks for the construction of new meta‐materials with tunable properties.

     

Glass transition and film formation of VeoVa/vinyl acetate latices; role of water and co-solvents

The physical forces causing deformation of latex particles during the film formation process have been witley studied. However, the forces resisting particle deformation are still poorly characterized. It is clear that the extent of particle deformation is dependent on the viscoelastic nature of the polymer. In an emulsion, the latex particles will normally contain water, surfactants and “free” monomers which lead to plasticization of the polymer. Although this effect has been recognized, so far it has been studied only on films that had been dried and then partially or completely swollen by water. In this work, plasticization of the emulsion polymers by water and co-solvent has been quantified via differential scanning calorimetry investigation directly on the aqueous latex dispersions. More specifically, the plasticizing effect of water on VeoVa/vinyl acetate copolymer latices and its influence on minimum film-forming temperature (MFFT) has been studied. A linear correlation has been found between T_g and MFFT for the wet latices. This new direct method should help to improve our understanding of the forces resisting latex film formation. Additionally, the homogeneous distribution of the hydrophobic and hydrophilic monomers (VeoVa and vinyl acetate respectively) in the latex particles was verified via a ¹³C-NMR (nuclear magnetic resonance) study performed directly on the latices. This study confirmed that no significant core/shell type of morphology had influenced latex film formation.