Nanofiber scaffolds of collagen have been fabricated via electrospinning using benign solvent systems as a replacement for 1,1,1,3,3,3 hexafluoro‐2‐propanol. Simple binary mixtures of phosphate‐buffered saline and ethanol have been found to be highly effective for electrospinning. FTIR spectra suggest that the triple helical structure of collagen was conserved after dissolution and electrospinning. Crosslinking of the electrospun collagen scaffolds was achieved with standard methods.
Green nanocomposite coatings based on renewable plant oils have been developed. An acid‐catalyzed curing of epoxidized plant oils with 3‐glycidoxypropyltrimethoxysilane produced transparent nanocomposites. The hardness and mechanical strength improved by incorporating the silica network into the organic polymer matrix, and good flexibility was observed in the nanocomposite. The nanocomposites showed high biodegradability.
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.
Summary: The polylactide‐based nano‐composites were prepared via melt extrusion method using different types of intercalants and nano‐fillers having different surface charge density. In order to understand the direct polymer melt intercalation into the nano‐galleries, the interdigitated layer structure of the organically modified layered filler (OMLF), where the intercalants are oriented with some inclination to the host layer in the interlayer space, was proposed. After polymer melt intercalation, the smaller initial interlayer opening led to the larger interlayer expansion, suggesting the large amount of the intercalation of the polymer chains. Consequently, the nano‐composite exhibited finer dispersion of the nano‐fillers when compared with the nano‐composites prepared from OMLFs with larger initial interlayer opening.
Illustration of a model of interlayer structure of the qC14(OH) in gallery space of HTO. 相似文献
A novel fluorescent nanoparticle with reversible on‐off switching properties has been synthesized. Three different wavelengths of light are used for switching‐on light, switching‐off light and excitation light, respectively. Thus, when this particle is used as a fluorescent probe by irradiation of the excitation light, the on‐off status can be maintained. We also showed that the on‐off status of the fluorescent particle even embedded in hydrogels can be remotely controlled by using two different wavelengths of light. These results promise that this kind of fluorescent particles will introduce a new concept and it will possibly be applied as a novel fluorescent probe, a photo memory, and a switching devise for photonics.
Nanoscale fibers with embedded, aligned, and percolated non‐functionalized multiwalled carbon nanotubes (MWCNTs) were fabricated through electrospinning dispersions based on melt‐compounded thermoplastic polyurethane/MWCNT nanocomposite, with up to 10 wt.‐% MWCNTs. Transmission electron microscopy indicated that the nanotubes were highly oriented and percolated throughout the fibers, even at high MWCNT concentrations. The coupling of efficient melt compounding with electrospinning eliminated the need for intensive surface functionalization or sonication of the MWCNTs, and the high aspect ratio as well as the electrical and mechanical properties of the nanotubes were retained. This method provides a more efficient technique to generate one‐dimensional nanofibers with aligned MWCNTs.
Electro‐spinning/netting (ESN) as a cutting‐edge technique evokes much interest because of its ability in the one‐step preparation of versatile nano‐fiber/net (NFN) membranes. Here, a controllable fabrication of polyurethane (PU) NFN membranes with attractive structures, consisting of common electrospun nanofibers and two‐dimensional (2D) soap bubble‐like structured nano‐nets via an ESN process is reported. The unique nanoscaled NFN architecture can be finely controlled by regulating the solution properties and several ESN process parameters. The versatile PU nano‐nets comprising interlinked nanowires with ultrathin diameters (5–40 nm) mean that the NFN structured membranes possess several excellent characteristics, such as an extremely large specific surface area, high porosity and large stacking density, which would be particularly useful for applications in ultrafiltration, special protective clothing, ultrasensitive sensors, catalyst support and so on.
In this paper, we report on the tunable metal‐enhanced fluorescence (MEF) of Ag nanostructures. Because of the good MEF properties of the highly dendritic Ag nanostructures, we obtained an increase of up to 25 times for the weak fluorescence of porphyrin molecules (Por4–). More importantly, by the introduction of a stimulus‐responsive PAA/PDDA multilayer film as an interlayer, the distance between the fluorophores and the Ag nanostructures could be tuned by immersing the substrates into solutions of different ionic strength or pH. The MEF behavior of the composite films could thus be tuned in a controlled manner, because of the distance dependent nature of the MEF effects.
Well‐defined diblock condensation copolymers composed of an aromatic polyamide and an aromatic polyether have been synthesized by means of successive chain‐growth condensation polymerizations. Polymerization of a polyamide monomer with an orthogonally difunctional initiator is accompanied with side reactions. On the other hand, polymerization with a monofunctional initiator afforded well‐defined polyamide, which has been converted into a macroinitiator by introduction of a terminal 4‐fluorobenzophenone unit. Well‐defined diblock copolymers are obtained by polymerization of a polyether monomer in the presence of this macroinitiator.
An amphiphilic biodegradable polymer, poly(aspartic acid‐co‐lactic acid) (PAL), was synthesized by simply heating a mixture of aspartic acid (Asp) and L ‐lactide without additional catalysts or solvents. The unique branched architecture comprising succinimide units and lactic acid units was confirmed by IR and NMR spectroscopy. A copolymer of sodium aspartate and lactic acid (PALNa) was prepared by reacting PAL with an aqueous sodium hydroxide solution. The PAL was soluble in many organic solvents, while the PALNa was soluble in methanol and water. The hydrolytic degradation behavior of PAL varied with the copolymer composition. A higher Asp content resulted in a faster molecular weight decrease, and introducing glycolic acid units accelerated the degradation rate.
For polymer synthesis upon visible light, actual photoinitiator operates in a restricted part of the spectrum. As a consequence, several photoinitiators are necessary to harvest all of the emitted visible photons. Herein, 2,7‐di‐tert‐butyldimethyldihydropyrene is used for the first time as a multicolor photoinitiator for the cationic polymerization of epoxides. Upon addition of diphenyliodonium hexafluorophosphate and optionally N‐vinylcarbazole, the originality of this approach is to allow efficient monomer conversions under various excitation light sources in the 360–650 nm wavelength range: halogen lamps, and light‐emitting and laser diodes. The synthesis of an interpenetrated polymer network from an epoxide/acrylate blend using a red light at 635 nm is also feasible. The formed polymer material exhibits a photochromic character.
Linear and crosslinked betaine‐type polyampholytes based on ethyl 3‐aminocrotonate and unsaturated carboxylic acids have been synthesized by very fast polymerization in bulk and solution. Bulk polymerization occurred exothermically even at room temperature and without adding an initiator. The polyampholytes showed stimuli‐responsive properties with respect to pH, ionic strength, water/organic solvent mixtures, and metal ion complexation.
Temperature profile of the polymerization reaction for an equimolar mixture of CRO and AA with time in the absence of initiator. 相似文献
New aromatic compounds with a pyridazine core have been synthesized. Four electron‐withdrawing monomers have been easily prepared from simple condensation reactions and ring closure procedures. Optimized HOMO, LUMO, and bandgap energy levels have been obtained. The resulting conjugated polymers have been tested in organic solar cells. First studies have revealed power conversion efficiencies up to 0.5% for an active area of 1.0 cm2.
Rheology and tribology become more and more critical issues in order to satisfy the harsh requirements for ultra‐small head/media spacing HDDs. In this communication, MD simulations with a bead/spring model were employed to examine the nano‐rheological response of nonfunctional and functional PFPEs by analyzing the shear viscosity of nanoscale PFPE films and the relaxation processes as a function of wall interaction/separation and endgroup functionality. Our simulation results indicate that thin PFPE films show more solid‐like behavior, especially under high shear rate. The film deformation and shear viscosity change by tuning the film thickness and the endgroup functionality was discussed in conjunction with the relaxation processes.
In the present paper, the microwave (MW)‐assisted synthesis of hydrogel forming polymers based on poly(acrylic acid) ( 1 ) is described. The polymer analogous condensation reaction between adamantyl moieties bearing free amino groups and poly(acrylic acid) ( 1 ) was carried out simply by mixing both components and subsequent use of MW protocol. The mixture was irradiated for 20 min without the addition of solvents or coupling agents. Aqueous solutions of the sodium salts of the obtained hydrophobically modified poly(acrylic acid)s showed a very high viscosity due to the intermolecular association of the hydrophobic side chains and the resulting formation of physical networks. By the addition of randomly methylated β‐cyclodextrin (RAMEB), the rheology of these systems could be influenced significantly.
Summary: A superhydrophobic coating was facilely fabricated in one step by casting bisphenol A polycarbonate (PC) solution under moisture. Vapor‐induced phase separation occurred during the solidifying process and a rough surface with a micro‐nano‐binary structure (MNBS) similar to the microstructure shown on lotus leaf was formed.
Low‐cost, responsive poly(N‐isopropylacrylamide)/polystyrene composite films were prepared by a facile electrospinning technique. The surface structures and wettabilities of the composite films are tunable by simply controlling the concentration of polymer. With a proper proportion of each polymer, the wettability of the surface can be switched between superhydrophilicity and superhydrophobicity when the temperature is changed from 20 °C to 50 °C. The combination of a stimuli‐responsive polymer with micro/nanostructures on the surface of the composite film contributes to this unique surface property.
Summary: The debate on the mechanism of dithiobenzoate‐mediated RAFT polymerization may be resolved by including the reaction between a propagating radical and the star‐shaped combination product from irreversible termination into the kinetic scheme. By this step, a highly reactive propagating radical and a not overly stable three‐arm star species are transformed into the resonance‐stabilized RAFT intermediate radical and a very stable polymer molecule. The time evolution of concentrations is discussed for the main‐equilibrium range of CDB‐mediated methyl acrylate polymerization.
Illustration of the novel understanding of the RAFT mechanism in dithiobenzoate‐mediated RAFT polymerization. 相似文献
