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This review summarizes the most widely used mechanisms in high-performance polymeric resistive memory devices, such as charge transfer, space charge trapping and filament conduction. In addition, recent studies of functional high-performance polymers for memory device applications are reviewed, compared and differentiated based on the mechanisms and structural design methods used. The reported memory properties show extremely high endurance during long-term operation, making high-performance polymers very suitable materials for memory applications.
A one-step synthesis of a well-defined mid-chain functional macrophotoinitiator of polystyrene- poly(ɛ-caprolactone) diblock copolymer (PSt-PI-PCL) was successfully performed at 110 °C using a dual-functional photoinitiator via simultaneous ATRP and ROP. The new dual-functional photoinitiator (Br-PI-OH) possessing a bromine group on one end and a hydroxyl group on the other, was synthesized by reaction of Irgacure 2959 photoinitiator (HO-PI-OH) with 2-bromopropanoyl bromide. The two distinct polymerization reactions proceeded in a controlled manner without mutual interference. Elemental analysis and 1H-NMR, 13C-NMR and Fourier transform infrared spectroscopy (FT-IR) spectroscopy were used to characterize the chemical structure of Br-PI-OH. Characterization of the macrophotoinitiator PSt-PI-PCL was achieved using 1H-NMR, FT-IR, gel permeation chromatography, UV-vis and fluorescence spectroscopy.
A polymer brush with exchangeable alkoxyamine side chains was prepared by surface-initiated atom transfer radical polymerization on silica nanoparticles. Fluorinated and ionic polymers were grafted to the polymer brush and the grafted side chains could be detached from the surface of the nanoparticles via radical exchange reactions of alkoxyamine moieties. The chemical composition of the polymer brushes on nanoparticles before and after the exchange reactions was investigated by X-ray photoelectron spectroscopy. The dispersibility of the nanoparticles in solution could be changed by the reversible grafting reactions.
Thermal annealing-induced crystallization in semi-crystalline poly(l-lactic acid) (PLLA) ultrathin films (referred as nanosheets) was investigated in terms of interfacial interaction of PLLA with air and substrate. The X-ray diffraction studies of the PLLA nanosheets with different thickness showed that the crystalline contents steeply increased below ca. 200 nm. These results indicated that the crystallization was enhanced near the surface of the air side and restricted near that of the substrate side due to the different interfacial association of the polymer chains in the nanosheet.
A composite gel composed of the C60 fullerene derivatives and poly(3,4-ethylenedioxythiophene)(PEDOT) was prepared using a low-temperature organic-solvent process. PEDOT was synthesized inside the C60-PEG gel and formed nanoscale junctions between C60 and PEDOT, which was beneficial for the movement of electrons and holes. The photocurrent was observed by irradiating the C60-PEG/PEDOT gel electrode with UV or simulated sunlight. Therefore, it is expected that the C60-PEG/PEDOT material is applicable for the photoelectric field, such as solar cells.
The laborious supercritical CO2 drying method limits the commercial availability of polymeric aerogels. Here we demonstrate a green and scalable method for the preparation of high-performance polyimide (PI) aerogels using low-boiling-point solvent mixture of tetrahydrofuran/methanol, and especially using sublimation drying instead of supercritical CO2 drying. Monolithic and powdery PI aerogels with nanofibrous morphology, low density and high thermal stability can be prepared facilely and thus facilitate their applications in many fields, especially high-temperature resistance, which are of essential importance.
Homogeneously dispersed states of the modified gold nanoparticles were obtained in the hydrogel with the interaction of the imidazolium units tethered to both the nanoparticle surfaces and the side chains of the networks. Initially, by swelling and shrinking the hydrogels, it was found that the absorption properties can be changed. Next, by using the photo-responsive mono-carboxylate linker, we observed the photo-triggered modulation of the absorption properties of the hydrogels. These results can be explained by the change of the interparticle distances of the nanoparticles in the hydrogel matrices.
We develop a novel strategy to reinforce an epoxy resin using carbon nanotubes (CNTs) as the filler material, in which polybenzimidazole (PBI) was used as the glue to enable an effective adhesion between the epoxy matrix and CNT surfaces. As the PBI strongly interacts with the surfaces of the CNTs and reacts with epoxy matrices to form covalent bonding, the PBI-wrapped CNTs are a promising material to reinforce the mechanical toughness of epoxy-CNT composites.
The molecular dynamics simulations of the telomeric single-stranded DNA (ssDNA) and protection of telomere 1 (POT1) in the single and biding states have been performed for 100 ns to compare the structures of those and to calculate root-mean-deviation, gyration radii, root-mean-square fluctuation and the number of hydrogen bonds. We found that the structures of the telomeric ssDNA in the single and binding states are different, and that one guanine and Gln94 are important for the binding system.
A β-sheet-forming peptide conjugated with a water-soluble moiety (polyethylene glycol (PEG) or a transactivator of transcription (TAT) sequence) forms rod-like aggregates in aqueous solution. We explored the detailed structures of the aggregates using Synchrotron X-ray scattering. We found that the β-sheet-forming peptide indeed formed stacked β-sheets, in a manner similar to that observed in the case of amyloid protofilaments. We also found that the resultant rod-like objects could be completely dispersed in water, as a result of the hydrophilicity of PEG or TAT.
A facile method of preparing cyclodextrin-grafted chitosan (CyD-g-CS) by means of the carboxymethlation of cyclodextrins and the dehydration-condensation reaction to chitosan was developed. In this method, crude product containing ~10% of the carboxymethylated-cyclodextrin was subjected to the grafting reaction without further purification. The product (CyD-g-CS) was finally purified by dialysis. Furthermore, doxorubicin-capturing nanoparticles composed of CyD-g-CS and sodium triphosphate were prepared.
The incorporated star-shaped four-armed stereo diblock poly(lactide) (4-LD) with poly(l-lactide) (PLLA) core and poly(d-lactide) (PDLA) shell and equimolar l- and d-lactide units formed stereocomplex (SC) crystallites and facilitated and accelerated the homo-crystallization of linear one-armed PLLA during heating and slow cooling and of linear one-armed PDLA during heating. The accelerating effect was higher for PLLA/4-LD with the opposite configurations of one-armed PLLA and the PDLA shell of 4-LD than for PDLA/4-LD with the identical configurations of one-armed PDLA and the PDLA shell of 4-LD.
Poly(l-3-hydroxybutanoic acid) [P(l-3HB)] and poly(d-3-hydroxybutanoic acid) [P(d-3HB)] in their equimolar blend crystallized synchronously and separately into each homo-crystallites but not stereocomplex crystallites. In the case of the blend, the orientation and periodical rotation of lamellae in the spherulites disappeared at a relatively low crystallization temperature (Tc); the nucleation for the spherulite growth was prolonged, and the size of homo-crystallites and the radial growth rate of spherulites were decreased, owing to the synchronous and separate homo-crystallization and the coexistence of P(l-3HB) and P(d-3HB) homo-crystallites in spherulites.
The impact strength of polyamide 11 (PA11) was improved by dispersing 10–30 wt% poly(butylene succinate) (PBS) without adding a compatibilizer, and no deterioration of the flexural modulus was occurred. The impact strength was controlled by the difference in shrinkage ratios between PA11 and PBS, and was three times that of neat PA11 (an increase from 13 to 40 kJ m−2). The mechanism of impact strength enhancement is discussed in terms of the formation of the dilational stress fields.
A 0.3-nm-high step pattern was formed on a poly(methyl methacrylate) (PMMA) polymer surface by thermal nanoimprinting a sapphire template. Large-area transcription was attained under the condition of ~0.2 MPa load for 300 s at 120 °C. We also observed the thermal deformation of the atomically stepped pattern formed on a PMMA surface by in situ atomic force microscopy at high temperature and found the atomic step pattern was stable near the imprinting temperature of 120 °C and also at about 20 °C higher than the bulk glass transition temperature of PMMA (105 °C).
