All issues / Volume 11 (2017) / Issue 2 (February)
This is an editorial article. It has no abstract.
Poly (ionic liquid)s (PILs) with a desirable tunability in their structures and properties have promising potentials to produce a hierarchically ordered functional materials. The structural evolution of imidazolium-based PILs with different counteranions during in-situ solvent evaporation has been investigated. Small angle X-ray scattering (SAXS) and X-ray diffraction studies indicate that upon solvent evaporation, poly [C16VIm+][Br–] displays a weakly ordered lamellar morphology and finally a hexagonal perforated lamellar structure. Over a wide range of dimethyl formamide (DMF) content, however, the poly [C16VIm+][BF4–]/DMF mixture shows a lamellar structure with a tiny minority of bicontinuous cubic phase that disappears instead in the corresponding dried samples caused by the decrease in space-filling requirement for alkyl chains arrangement. For poly [C16VIm+][PF6 –], there is almost no change in inner structures with solvent evaporation except a more ordered lamellar morphology observed in the dried sample. Notably, an interdigitated packing of alkyl tails dominates the lamellar sheets for all dried PIL samples. These results indicate that the design and fabrication of PIL assemblies with ordered structures can be achieved by simply changing counteranion and solvent content, which offers a feasible approach for engineering PIL-based nano-scale functional materials.
A series of poly(N-isopropylacrylamide-co-acrylamide) thermoresponsive random copolymers with different molecular weights and composition were synthesized and characterized by attenuated total reflectance Fourier-transform infrared (ATR-FTIR), differential scanning calorimetry (DSC), size exclusion chromatography (SEC) and proton nuclear magnetic resonance (NMR) spectroscopy. The lower critical solution temperatures (LCST) of the copolymers were tuned by changing the mole ratios of monomers. Copolymer with highest molecular weight and LCST (41.2 °C) was grafted on SBA-15 type mesoporous silica particles by a two-step polymer grafting procedure. Bare SBA-15 and the thermoresponsive copolymergrafted (hybrid) SBA-15 particles were fully characterized by scanning electron microscope (SEM), ATR-FTIR, thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller (BET) analyses. The hybrid particles were tested for their efficiency as temperature-sensitive systems for dermal delivery of the antioxidant rutin (quercetin-3-O-rutinoside). Improved control over rutin release by hybrid particles was obtained which makes them attractive hybrid materials for drug delivery.
Composite electrodes consisting of TiO2 nanoparticles (NPs)-TiO2 nanorods (NRs) and poly (3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS) were prepared on a conductive glass substrate. The presence of TiO2 in the composite structure was proved by X-ray diffraction (XRD) Raman and FTIR-ATR measurements. The surface morphologies of TiO2 NP-PEDOT:PSS, TiO2 NR-PEDOT:PSS and TiO2 NP-TiO2 NR-PEDOT:PSS electrodes were characterized by scanning electron microscopy (SEM). According to the cyclic voltammetry measurement (CV), the electrocatalytic activity of composite electrodes on the reduction of triiodide improved after TiO2 addition compared with pristine PEDOT:PSS and platinum (Pt) electrodes. Electrochemical impedance spectroscopy (EIS) showed that the charge transfer resistance (Rct) strongly depends on the morphologies (ratio between TiO2 NP and TiO2 NR) of the composite electrodes. It was found that Rct decreased by increasing the amount of TiO2 nanorod in the whole mixture of TiO2 nanoparticles and PEDOT:PSS.
Despite numerous studies on fatigue of polymer materials under variable loading, there is little work on highdensity polyethylene (PE-HD). In this context, an experimental analysis for determining the fatigue strength of PE-100, under constant and variable amplitude loading is presented. Further, the cumulative fatigue damage behavior of PE-100 was experimentally investigated. First, the fatigue curve (S-N: stress vs. number of cycles) was obtained in order to establish the fatigue life of PE-100 subjected to constant stress amplitude. Secondly, Miner’s fatigue rule as well as stress-based and energy-based fatigue damage models were used to estimate the cumulative variable amplitude fatigue damage. Comparison between predictions and experimental results showed different trends depending on the choice of prediction model used implying careful fatigue damage consideration when designing under variable amplitude loading.
Three water-dispersable composites have been synthesized by in situ chemical oxidative polymerization of aniline N-propanesulfonic acid (AnS) in reduced graphene oxide (r-GO) dispersion, in an ice bath at 0 °C and in the absence of any surfactant. The mass ratio between r-GO and aniline monomer have been established as (mr-GO:mAnS) = 1:1, 1:2 and 1:5 while in the composites, the mass ratio between r-GO and polyaniline was found: 1:0.3, 1:0.5 and 1:1, respectively. The molecular structure, morphology, and optical properties of the composites were analyzed through Fourier transform infrared (FTIR), Raman and ultraviolet-visible (UV-Vis) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Electrochemical performances for energy storage were evaluated by cyclic voltammetry and galvanostatic charge/discharge measurements with 1M H2SO4 as electrolyte in a three-electrode cell. The composite with the mass ratio (mr-GO:mPAnS) = 1:1 has showed good capacitive behavior with a specific capacitance of 1019 F/g at scan rate of 1 mV/s calculated from integrated area of cyclic voltammogram curve and a retention life of 80% after 100 cycles. These results indicate that the composites prepared by chemical oxidative polymerization are promising materials for electrode supercapacitors.
Brush-shaped block copolymer with a dual hydrophilic poly(acrylic acid)-block-poly(oligo(ethylene glycol) acrylate) (PAA-b-POEGA) arms was synthesized for the first time via a simplified electrochemically mediated ATRP (seATRP) under both constant potential electrolysis and constant current electrolysis conditions, utilizing only 30 ppm of catalyst complex. The polymerization conditions were optimized to provide fast reactions while employing low catalyst concentrations and preparation of cellulose-based brush-like copolymers with narrow molecular weight distributions. The results from proton nuclear magnetic resonance (1H NMR) spectral studies support the formation of cellulose-based graft (co)polymers. It is expected that these new polymer brushes may find application as pH- and thermo-sensitive drug delivery systems.
The target of the present study was to investigate the structure-property relationships of heterophasic ethylenepropylene (EP) copolymers based on a single-site (metallocene) catalyst (SSC) supported with an emulsion technology developed by Borealis. The structure of these copolymers, their morphology evolution, as well as resulting mechanical properties were studied by varying the composition of the dispersed phase, i.e. the amorphous ethylene-propylene copolymer or rubber (EPR), in a systematic series of bench-scale products. Next to composition effects, an attempt was made to understand the key differences between products based on Ziegler-Natta catalysts (ZNC) and single-site catalysts (SSC) in terms of polymer structure and property profile. A remarkably different phase morphology with very good phase coupling to the matrix PP and the absence of crystallizable polyethylene in the ethylene-rich copolymers (EPR) was observed for the SSCbased grades, resulting in a high level of impact strength over a wide composition range.