Summary: Silvered polyimide films have been fabricated by direct ion exchange of a damp‐dry poly(amic acid) film with an aqueous silver solution such as silver nitrate. Thermal curing of the silver(I )‐containing films under tension leads to cycloimidization of the poly(amic acid) into polyimide with a concomitant silver(I ) reduction and aggregation at both film sides to give reflective and conductive double‐surface‐silvered polyimide films. The metallized films retain the essential properties of the parent polyimide.
Surface morphology of the prepared double‐surface‐silvered polyimide films. 相似文献
A simple synthetic method has been developed for the fabrication of antimicrobial polyrhodanine nanotubes with silver nanoparticles. Rhodanine monomer first forms one‐dimensional complexes with silver ions due to coordinative interactions and consecutively reduces the silver ions during chemical‐oxidation polymerization. The polymerization procedure is analyzed by transmission electron microscopy and scanning electron microscopy in situ. The synthesized silver nanoparticles/polyrhodanine nanotubes are applied as an antimicrobial agent against Gram‐negative bacteria, E. coli and Gram‐positive bacteria, S. aureus. The antimicrobial tests demonstrate that the silver/polyrhodanine nanotubes have superior antimicrobial properties to silver nanoparticles and rhodanine monomer.
DNA hydrogels which are composed of an entangled network without a crosslinker are synthesized and examined in regards to their sensitivity to salt and pH changes. The DNA hydrogel fibers only exhibited a marked response – that is a fast and large change in length – under biological conditions ([Na+] = 0.15 M at pH = 7) and are therefore suitable materials for bio‐inspired devices.
Summary: From kinetic theory we have rigorously derived singularity‐free Brownian dynamics analyses of nanoparticle rotational dynamics. The rigid non‐spherical nanoparticles incorporate all three rotational degrees of freedom. This was achieved by using the components of Cartesian rotation vectors as the generalized coordinates describing angular orientation. The new results constitute an important advance compared to the situation when Eulerian angles specify angular orientation. Our finding eliminates one of the main longstanding obstacles to detailed studies of nanoparticle rotational dynamics in the diffusion time domain. The described formalism is applicable to a wide range of nanoparticle systems including liquid crystals, biopolymers, and colloids.
The mechanistic interpretation of kinetic anomalies in reversible addition–fragmentation chain transfer (RAFT)‐mediated polymerization is critically reviewed. The main conclusion of this exercise is that available data do not allow model discrimination between the two prevailing mechanistic schemes, i.e., the slow fragmentation model and the intermediate radical termination model. However, assessment of the rate parameters reveals that the incompatibilities may not be as large as previously reported in literature. Dedicated kinetic studies on model compounds should be performed to shed further light on the seemingly incompatible data that currently exists in literature.
A close correllation between molecular‐level interactions and macroscopic characteristics of polymer networks exists. The characteristics of the polymeric hydrogels assembled from β‐cyclodextrin (β‐CD) and adamantyl (AD) substituted poly(acrylate)s can be tailored through selective host–guest complexation between β‐CD and AD substituents and their tethers. Dominantly, steric effects and competitive intra‐ and intermolecular host–guest complexation are found to control poly(acrylate) isomeric inter‐strand linkage in polymer network formation. This understanding of the factors involved in polymeric hydrogel formation points the way towards the construction of increasingly sophisticated biocompatible materials.
We describe an enzyme‐responsive polymeric vehicle, which is of great interest in controlled drug delivery, biosensing, and other related areas. The polymer synthesized using lipase as catalyst in DMSO has a favorable molecular structure that is quickly hydrolyzed by lipase in aqueous phase, and allows a fast release of encapsulated molecules.
A ‘grafting‐from’ approach to synthesize microparticle‐supported conjugated polyelectrolyte brushes is presented. Poly(3‐bromohexylthiophene) is selectively grown from monodisperse organosilica microparticles by surface‐initiated Kumada catalyst‐transfer polycondensation (SI‐KCTP) and then ionizable amino groups are introduced by a two‐step polymer analogous transformation. Optical properties of the resulting microparticle‐supported conjugated polyelectrolyte brushes were found to be dependent on the surrounding chemical environment and thus the particles are promising materials for sensor applications.
A simple approach to improve the structural ordering in block copolymer/nanoparticle nanocomposites is presented. It is to blend a small molecular weight homopolymer with the composites, which can uniformly swell the preferred domain where the nanoparticles locate and increase the conformational entropy of the domain. Consequently, the interfaces between the block copolymer domains become smooth that improves the long range order in the nanocomposites. Furthermore, the uniform swelling of the preferred domain by the homopolymer will allow higher loading of nanoparticles without adversely affecting the long range order.
The deformation and breakup of a single polycarbonate drop in a polyethylene matrix is studied at high temperatures under simple shear flow using a transparent Couette device. We observed “parallel breakup” where the drop breaks after being stretched into a thin sheet parallel to the flow. The breakup occurs at a viscosity ratio greater than 3.5. Deborah number and a stress ratio incorporating elastic moduli can characterize the “parallel breakup”.
Deformation and breakup of a polycarbonate drop in a polyethylene matrix. 相似文献
Well‐dispersed silver nanoparticles were successfully fabricated within poly[(N‐isopropylacrylamide)‐co‐(acrylic acid)] [P(NIPAM‐co‐AA)] microgel particles which were synthesized with different cross‐linking densities. Their structures were studied by field‐emission scanning electron microscopy, transmission electron microscopy, UV‐vis spectroscopy, X‐ray diffraction and FT‐IR spectroscopy. The interactions between the microgel particles and the incorporated silver nanoparticles were investigated by X‐ray photoelectron spectroscopy. The results revealed that there was charge transfer from the carbonyl groups of the microgel particles to the silver nanoparticles. Moreover, as the diameter of the AgNPs decreases, the charge‐transfer efficiency increases accordingly. The P(NIPAM‐co‐AA)/AgNPs hybrid microgel particles were thermoresponsive and their behavior completely reversible with several heating/cooling cycles.
One‐dimensional methyl orange fibrils can be easily prepared. They are stable in acidic aqueous solutions and soluble in neutral water. When used to synthesize conducting polymer microtubules, the fibrils act as “hard templates” formally but as “soft templates” effectively. Microtubular structures of polypyrrole, polyaniline, and poly(3,4‐ethylenedioxythiophene) have been achieved successfully via such water‐soluble versatile templates.
A single stage electrospinning process can give rise to preferentially oriented induced dipoles in poly(vinylidene fluoride‐trifluoroethylene) [P(VDF‐TrFE)] nanofibers. The piezoelectricity of as‐electrospun P(VDF‐TrFE) nanofiber webs opens up new possibilities for their use as a flexible nanogenerators and nano‐pressure sensors. In this work, the origin of the piezoelectricity has been spotlighted by randomization of the induced dipoles at the Curie temperature and analyzed by polarized FT‐IR spectroscopic techniques as well as by detecting the piezoelectric signal from a nano‐pressure sensor.
Nanostructures with stimuli‐responsive properties are of great importance for the application of smart materials in nanotechnology. Unique hollow polypyrrole nanostructured arrays with a conical shape have been produced by a stepwise electropolymerization process. The polypyrrole conical nanocontainers exhibit a reversible switchable behavior between open and closed states, which is controlled by the movement of counter ions during electrically controlled reversible oxidation and reduction processes. The formation of conical nanocontainers is affected by the oleo‐wettability of the substrate. Conical nanocontainers can be formed on oleo‐phobic substrates in aqueous solution by using dopant‐stabilized pyrrole nanodroplets as the guiding template for the polymerization.
Polymerized ionic liquid (PIL) nanoparticles are for the first time applied as sole stabilizers in aqueous emulsion polymerization and reveal an astonishing and unexpected behavior. In a well‐dispersed state, the PIL nanoparticles serve as an unexpectedly effective stabilizer for polystyrene dispersions, enabling solids content of greater than 40%. However, the same PIL as dry powder is hydrophobic and, in accordance with Bancroft's rule, unable to stabilize aqueous dispersions. This ambivalent behavior of PIL is extremely beneficial for the application of aqueous dispersions because, as desired for decades, the hydrophilic dispersed state during synthesis turns hydrophobic in the dried state during application of the polymer.
POSS‐functionalized polyisobutylenes (PIBs) were synthesized by carbocationic polymerization using an epoxy‐POSS/TiCl4 initiating system in hexane/methyl chloride (60:40 v/v) solvent mixture at −80 °C. 1H NMR spectroscopy verified the incorporation of one epoxy‐POSS per polymer chain. Light scattering and TEM analysis demonstrated the formation of 50–100 nm sized aggregates and micron‐sized clusters.
