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.
Summary: A new strategy was developed to prepare disorderly exfoliated nanocomposites, in which a soft siloxane surfactant with a weight‐average molecular weight ( ) of 1 900 was adopted to modify the clay. The modified clay slurry was then mixed with silicone rubber by hand, and exfoliation was achieved. The proposed mechanism thereof was verified by TEM and XRD. The physical entanglement of the soft siloxane surfactant plays a vital role in the diffusion and intercalation of the matrix molecules during the compounding of the slurry‐polymer mixture. This simple method is applicable to other silicone‐based materials reinforced by clay.
TEM micrograph of silicone rubber/clay‐sil nanocomposite. 相似文献
The use of a photocatalyst (tris(2‐phenylpyridine)iridium [Ir(ppy)3]) being able to generate both radicals and cations to initiate free radical polymerization and ring opening polymerization is presented. Remarkably, under soft irradiations (fluorescence bulb, sunlight), excellent cationic polymerization profiles and final conversions are obtained. The involved mechanisms are investigated by ESR experiments.
A new approach for the estimation of kinetic rate constants in olefin polymerization using metallocene catalysts is presented. The polymerization rate has been modeled using the method of moments. An ANN has been used and trained to behave like the mathematical model developed before, so that it gets polymerization rate at different reaction times and predicts reaction rate constants. The network was trained using modeling results in desired operational window. The polymerization rates were normalized to make the network work independent of operational conditions. The model has also been applied to real polymerization rate data and the predictions were satisfactory. This model is specially useful in comparing different new metallocene catalysts.
Summary: Brillouin light scattering (BLS) from submicron‐size patterned polyurethane (PU) films was found to display rich spectral features. Their identification allows the determination of the mechanical properties of the PU and the characterization of the periodicity and the coherence of the structure. A temperature‐dependent study demonstrates that BLS is a sensitive tool to monitor changes of the mechanical properties and/or of the morphology.
(a) Scheme of the sample structure and the scattering geometry, (b) SEM top view of the PU features. 相似文献
With combinatorial materials research (CMR), a new research approach toward the development and optimization of materials has been established at BASF. While adopting the basic ideas of combinatorial chemistry, CMR faces a whole bunch of challenges throughout the entire combinatorial process loop. New concepts for sample preparation on a smaller scale, i.e. synthesis and formulation, for parallel or fast sequential screening and characterization, and for appropriate management of yet unknown amounts of data have been developed. The integration of as many as possible workflow steps and the interplay of experts from various relevant fields, such as chemistry, engineering, robotics, informatics, and physics, are necessary. First results in the fields of polymer synthesis and coatings formulation give an impression of the innovative power and efficiency of this new kind of research.
Summary: Polyelectrolyte multilayer microspheres were prepared by alternating adsorption of dextran sulfate and protamine on melamine formaldehyde cores followed by the partial decomposition of the core. Peroxidase and glucose oxidase were immobilized in the prepared microspheres. Retention of enzymatic activity of the peroxidase/glucose oxidase system incorporated into the microspheres was demonstrated. Applicability of the bienzyme system immobilized in the microspheres for kinetic glucose assay was shown.
SEM image of the polyelectrolyte multilayer microsphere. 相似文献
A series of selenophene oligomers incorporating conjugated fluorinated phenylene units have been synthesised as potential semiconductor materials for organic field‐effect transistors (OFETs). X‐ray crystallography shows that the molecules are held in close proximity by several short intermolecular contacts, making them ideal candidates for OFET applications.
A thiol‐modified siRNA targeting the enhanced green fluorescence protein (eGFP) gene was conjugated with RAFT‐synthesized, pyridyl disulfide‐functional poly(PEG methyl ether acrylate)s (p(PEGA)s). siRNA‐p(PEGA) conjugates demonstrated significantly enhanced in vitro serum stability and nuclease resistance compared to the unmodified and thiol‐modified siRNA. The complexes of siRNA‐p(PEGA) conjugates with a fusogenic peptide, KALA ((+)/(–) = 2) inhibited the protein expression approximately 28‐fold more than the KALA complex of the unmodified siRNA. The protein inhibition caused by siRNA‐p(PEGA)‐KALA complexes (56 ± 5%–58 ± 3% of the fluorescence expressed in non‐treated cells) was comparable to the effect of the unmodified siRNA‐lipofectamine complex (77 ± 7%).
We report novel nanoporous polyimides formed from jungle‐gym‐type rigid polyimide gels by supercritical CO2 drying. By virtue of supercritical CO2 drying to avoid the collapse of nanostructure, porosity above 90 vol.‐% was achieved. We found a rich variety of nanoporous structures in the range of 50–800 nm such as crisp fragments, minute network, and highly‐connected beads. These characteristic structures were formed by the competitive progress of liquid‐liquid phase separation and crystallization induced due to the two chemical reactions of end‐crosslinking and thermal imidization during gelation.
A novel method of macromolecule encapsulation using micron‐sized polymeric shells constructed with a photoactive azobenzene containing polyelectrolyte is discussed. Fluorescently labeled dextran molecules were encapsulated using light to remotely shrink and change the wall permeability of new polymeric hollow shells. We observed that the proportion of shells with dye encapsulated increased along with the duration of irradiation. Electron microscopy imaging illustrated significant changes in the surface roughness of shells after being exposed to light. Finally, this new system was shown to possess a high thermal stability.
Organic polymers that contain ligated metals offer a variety of unique properties which include luminescence, electro‐ and photochemistry, catalysis, charge, magnetism, and thermochromism. These organic–inorganic hybrid materials have the potential to offer novel active matrixes for advanced devices. Continued progress in synthetic chemistry and molecular characterization will enable such advanced materials. Here the focus is restricted to side‐chain metal complexes with emissive properties that highlight the use of lanthanide ions as opposed to the often‐studied transition metal complexes.
