Blends of polyamide 12 and small amounts (0.15–1 wt%) of the excimer‐forming fluorescent dye 1,4‐bis(α‐cyano‐4‐octadecyloxystyryl)‐2,5‐dimethoxybenzene (C18‐RG) are produced by melt‐processing. While green monomer fluorescence from well‐individualized chromophores is observed at low dye concentration (0.15%), higher dye concentrations lead to aggregation of the dye so that the emission characteristics are dominated by red excimer fluorescence. Upon mechanical deformation of samples with appropriately selected dye content (0.25 wt%), a pronounced mechanochromic effect can be observed, which manifests itself through a mechanically induced transformation from excimer‐dominated to monomer‐rich emission. The monomer to excimer emission ratio IM/IE is increased by a factor of up to 2 in a step‐wise manner when samples are uniaxially deformed past the yield point.
Mechanically robust and self‐healing rubbers are highly desired to satisfy the increasing demand of high‐performance smart tires and related materials. Herein, a self‐healing rubber nanocomposite with enhanced mechanical and self‐healing performance based on Diels–Alder chemistry has been investigated. The furfuryl grafted styrene‐butadiene rubber and furfuryl terminated MWCNT (MWCNT‐FA) are reacted with bifunctional maleimide to form a covalently bonded and reversibly cross‐linked rubber composite. Obvious reinforcing effect is obtained at high cross‐linking density. Over 200–300% increase in the Young's modulus and toughness can be achieved in the rubber nanocomposites with 5 wt% MWCNT‐FA. Meanwhile, the healing efficiency increased with MWCNT‐FA content. MWCNT‐FA plays dual roles of effective reinforcer and a kind of healant.
A 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO)‐triazine based anhydride (2,4,6‐tris‐(DOPO‐methylformatephthalic anhydride‐phenoxy)‐1,3,5‐triazine (TDA)) is synthesized and used as a halogen‐free flame retardant co‐curing agent for diglycidyl ether of bisphenol A/methylhexahydrophthalic anhydride (DGEBA/MHHPA) system. The conjugation of anhydride group is increased by the utilization of TDA, leading to the reduction in the curing activation energy. The cured epoxy resin passes V‐0 rating of UL 94 test with the limiting oxygen index of 32.7 vol% when the phosphorus content is only 1.5 wt%. The flame‐retarding action of triazine ring and DOPO moiety is investigated by the residue analysis and the characterization of pyrolysis gas. Due to the presence of bulky aromatic subunits in the molecular structure of TDA, the flame‐retarded epoxy resins maintain the high glass transition temperature of DGEBA/MHHPA. Besides, the moisture absorption is diminished following the usage of TDA.
Nanofiber‐based hydrocolloid scaffold is prepared by colloid electrospinning of thermoplastic polyurethane (TPU)/sodium carboxymethyl cellulose (S.CMC) in tetrahydrofuran (THF)/dimethylformamide (DMF). The most suitable process of electrospinning for successful formation of fibers is investigated by controlling the concentration of polymeric solution and co‐solvent ratio. In order to accomplish high wettability, the amount of colloid (S.CMC) and the co‐solvent ratio (THF/DMF), which affects the morphology of fibers, are adjusted. Finally, the open wound healing effect is confirmed using nanofiber‐hydrocolloid from in vivo animal studies. A detailed study of the wound healing process is also demonstrated for the first time.
A new facile approach for the fabrication of polymer‐Ag honeycomb film is reported. A polymer‐Ag+ honeycomb thin film is obtained by casting a CHCl3 solution of a functional graft copolymer on aqueous silver nitrate solution, leading to metal complexation induced phase separation at the air/water interface. The film is reduced by UV irradiation to give a polymer‐Ag honeycomb film with regular morphology. Pyrolysis of the film gives a translucent Ag honeycomb film.
The introduction of nanodiamond particles (NDs) in silane‐crosslinked polyethylene is found to lead to a notable and systematic deformation of the polymer unit cell. X‐ray diffraction evidence of the existence of a modified crystalline structure in the bulk of the polymer due to the presence of NDs is reported here for the first time. The covalent bonding between NDs and the surrounding macromolecular chains may support that the excessive local stress field ultimately distorts the polymer conformation, yielding a new distorted but still crystalline interface. Supporting data from solid‐state NMR experiments confirm the existence of a modified crystalline interface of about 1–2 nm in all the nanocomposite materials.
The flame retardancy and mechanical properties of polyamide‐6 (PA6)/aluminum diethylphosphinate (AlPi) composite are greatly improved by the addition of novelly synthesized phosphorus flame retardant‐based diepoxide (DEP) during extrusion. The PA6/AlPi/DEP composite passes V‐0 rating of UL94 test with limiting oxygen index (LOI) of 32.6% at 13 wt% AlPi and 1 wt% DEP, as revealed by the results of flammability. The synergistic flame retardation mechanism offered by the two additives (AlPi and DEP) is studied in terms of in‐depth characterization of the charred residue and evolved gas. The deteriorated mechanical strength of PA6 due to existence of AlPi is compensated by the simultaneous chain extension effect of DEP. Accordingly, the flexural and impact strengths of PA6/AlPi/DEP composite are even superior to those of neat PA6.
Interfacial polymerization of dopamine and terephtaloyl chloride is performed on a porous crosslinked polyacrylonitrile support membrane. The resulting polymer layer has a smooth surface and is ultrathin (about 5 nm). The chemical nature of the interfacially polymerized layer is characterized by Fourier transform infrared spectroscopy and by X‐ray photoelectron spectroscopy. The thin‐film composite membrane is stable in aggressive solvents like dimethylformamide (DMF) and the membrane shows high solvent permeances combined with a molecular weight cut‐off below 800 g mol‐1. The remarkable stability in DMF, the ease of preparation as well as the extremely thin and smooth selective layer make this new type of bioinspired membrane attractive for solvent resistant nanofiltration.
Silicone materials are widely used in many fields such as electrical or food industries and their consumption is constantly growing. They are generally cured by vulcanization reaction for long time at high temperatures which requires high energy consumption. The possibility to achieve the polymerization of silicone rubbers by UV‐activation promotes the reduction of both time and temperature leading to an impressive energy saving. Indeed, this process is more than 30 times faster than the thermal one. Moreover, the properties of the two resulting materials are comparable, indicating that the low time of UV‐activated hydrosilation reaction is suitable for the formation of crosslinked silicone polymers.
Porous polymer materials prepared from biodegradable polymers have received considerable attention due to their potential as cell culture scaffolds for tissue engineering. Porous materials are generally sterilized by autoclaving prior to use as cell culture scaffolds to avoid unexpected biological infection. However, the melting point of biodegradable polymers is typically lower than the temperature used in autoclave sterilization. Here, the preparation of honeycomb films comprising a poly(L‐lactic acid) (PLLA) and poly(D‐lactic acid) (PDLA) stereo complex is described and their thermal stabilities are evaluated. The hierarchic photochemical patterning of PLLA/PDLA stereo complex honeycomb‐patterned films by UV‐O3 treatment is also demonstrated.
The present work focuses on the influence of nucleation processes on the crystallization of bio‐based poly(ethylene 2,5‐furandicarboxylate) (PEF). Nuclei formation has been studied by means of fast scanning calorimetry (FSC) both when cooling from the melt (nonisothermal conditions) and when annealing at either low‐ or high‐temperatures (isothermal conditions). FSC results show that nucleation on cooling can be prevented by using fast rates allowing to keep the polymer in its amorphous state; whereas cooling at moderate rates results in sample nucleation with a subsequent increase of the crystallization rate. Isothermal pretreatment just above the PEF glass transition temperature (Tg) results in nuclei formation whose rate decreases when the nucleation temperature approaches PEF Tg. On the other hand, annealing below the PEF melting point allows determination of the sample self‐nucleation behavior which occurs in a very narrow temperature range, i.e., between 195 and 198 °C.
Electrospinning of sulfur‐free softwood lignin (SFSL) in N,N‐dimethylformamide (DMF) is reported as is and with poly(ethylene oxide) (PEO). SFSL macromolecules behave as rigid spheres, instead of free draining macromolecules in DMF. Hence they are investigated as colloids. Colloidal SFSL generates uniform fibers only at the volume fraction of 0.63. It is due to the sufficiently high longest mean relaxation time at the volume fraction of 0.63. Colloidal SFSL below the volume fraction of 0.63 does not exhibit any measurable viscoelasticity and also does not generate any uniform fibers. Bead‐free fibers are generated at volume fractions below 0.63 only by adding PEO. PEO presence brings elasticity to colloidal SFSL and produces bead‐free fibers only above the entanglement concentration of PEO in DMF. The presence of SFSL macromolecules does not cause any interactions with PEO molecules, except it reduces the available of free volume for PEO chains in DMF.
Hydrophobic and super‐hydrophobic materials have many important applications, but most of the artificially hydrophobic and super‐hydrophobic surfaces suffer from poor durability. Herein, a facile method is reported to fabricate robust hydrophobic and super‐hydrophobic polymer films through backfilling the silica colloidal crystal templates with the mixture of fluoropolymer, thermoset hydroxyl acrylate resins, and curing agent. After removal of the template, 3D ordered porous structures are obtained. The obtained polymer films have not only excellent hydrophobic or super‐hydrophobic properties but also good stability against temperatures, acids, and alkalis. Dual ordered porous structure can obviously enhance the hydrophobicity of polymer films compared to unitary one.
Dopamine is a molecule that facilitates biomineralization, and it is used to prepare electropolymerization‐induced polydopamine (PDA). For the first time, dopamine is used for template‐free electrochemical polymerization to form biocompatible polypyrrole (PPy) nanofiber coatings on bone implants. Dopamine monomers are electropolymerized to PDA chains affixed to biomedical titanium after the nanomicelles are tuned to self‐assemble by triggering the potential, resulting in nanofiber formation. Dopamine serves as a dopant to induce the formation of conductive PPy nanofibers and as a promoter to accelerate biomineralization, cell proliferation, and adhesion.
Using synchrotron‐radiation X‐rays for nanoscale computed tomography (X‐ray nano‐CT), the structure and corresponding reinforcement effects of carbon black (CB) filler at various amounts in natural rubber (NR) are studied during cyclic loading. All structural parameters of the CB filler, which are extracted from X‐ray images—such as the destruction and reconstruction ratios of the aggregates and the network connectivity, show a transition point with the CB content at around 30 phr (phr = parts by weight per hundred parts of rubber). When the CB content is above the transition point, the effective volume fraction exceeds the percolation threshold, and a stress‐bearing filler network can form; this network can effectively transmit the external stress to the entire sample and abruptly enhance the reinforcement factor. Below the percolation threshold, the CB filler is mainly disconnected aggregates, where its reinforcement of the rubber matrix can be mainly described by the volume‐filling effect. Using the dynamic cluster–cluster aggregation (CCA) model, calculations of the mechanical properties related to the CB content suggest that the network structure plays a major role in the reinforcement of the NR.
Four bromine‐containing methacrylates 1 – 4 are synthesized from pentaerythritol tribromide and 2,2,2‐tribromoethanol and are characterized by 1H and 13C NMR spectroscopy. Their free radical polymerization is performed in dimethylformamide (DMF), using 2,2′‐azobis(2‐methylpropionitrile) as initiator. The photopolymerization behavior of monomers 1–4 is investigated using a differential scanning calorimeter. Homopolymerizations and copolymerizations with 2‐hydroxyethyl methacrylate are carried out. Both the presence of a carbamate group and of bromine atoms result in an increase of the polymerization rate. Dental resins are prepared by replacing a certain amount of 2‐(4‐cumyl‐phenoxy)ethyl methacrylate by monomers 3 and 4 in a model formulation. The incorporation of these methacrylates leads to a significant increase of the radiopacity. Resins based on monomer 4 exhibit improved mechanical properties.
A conjugated polymer, poly(9,9‐bis(6‐bromohexyl)‐9H‐fluorene‐alt‐1,4‐phenylene), is synthesized, converted to nanoparticles via a nanoprecipitation process, and utilized to fabricate thin films including conjugated polymer nanoparticles. The nanoparticles with surface bromides can be conjugated with an amine‐functionalized dendrimer via a nucleophilic coupling reaction. Thus, when microliter solutions of the particulates are dragged at a constant velocity on substrates alternately in a layer‐by‐layer manner, thin films composed of the nanoparticles and dendrimers can be successfully built up on the substrates. Our results suggest a methodology to control the deposition of thin films bearing conjugated polymer nanoparticles while minimizing processing time and decreasing material consumption.
A self‐cleaning membrane that periodically rids itself of attached cells to maintain glucose diffusion could extend the lifetime of implanted glucose biosensors. Herein, we evaluate the functionality of thermoresponsive double network (DN) hydrogel membranes based on poly(N‐isopropylacrylamide) (PNIPAAm) and an electrostatic co‐monomer, 2‐acrylamido‐2‐methylpropane sulfonic acid (AMPS). DN hydrogels are comprised of a tightly crosslinked, ionized first network [P(NIPAAm‐co‐AMPS)] containing variable levels of AMPS (100:0–25:75 wt% ratio of NIPAAm:AMPS) and a loosely crosslinked, interpenetrating second network [PNIPAAm]. To meet the specific requirements of a subcutaneously implanted glucose biosensor, the volume phase transition temperature is tuned and essential properties, such as glucose diffusion kinetics, thermosensitivity, and cytocompatibility are evaluated. In addition, the self‐cleaning functionality is demonstrated through thermally driven cell detachment from the membranes in vitro.
The previously introduced process for enzyme‐mediated in situ synthesis and deposition of eumelanin is investigated with covalent immobilization of the tyrosinase. It results in a monolayer structure of non‐coalesced melanin particles, with a film thickness of 5–8 nm. The reaction is self‐terminating due to overlay of the enzymes with particles. The melanin particles are rodlike with lengths down to 6 nm. Isolated melanin structures of such small size have not been observed before and might be a kind of protoparticle in the supramolecular buildup of melanin oligomers. Utilization of melanin particles with such small size can enable nanotechnological applications in the areas of bioelectronics and biosensors.
The polyacrylonitrile/polymethyl‐methacrylate (PMMA/PAN) porous fibers, core–shell hollow fibers, and porous thin films are prepared by coaxial electrospinning, single electrospinning, and spin‐coating technologies, respectively. The different morphologies arising from different processes display great influences on their thermal and crystalline properties. The adding of PMMA causes porous structure due to the microphase‐separation structure of immiscible PMMA and PAN phases. The lower weight loss, higher degradation temperature, and glass‐transition temperatures of porous thin films than those of porous fibers and core–shell hollow fibers are obtained, evidencing that the polymer morphologies produced from the different process can efficiently influence their physical properties. The orthorhombic structure of PAN crystals are found in the PMMA/PAN porous thin films, but the rotational disorder PAN crystals due to intermolecular packing are observed in the PMMA/PAN porous fibers and core–shell hollow fibers, indicating that different processes cause different types of PAN crystals.
下载免费PDF全文