Large scale load of phosphotungstic acid on multiwalled carbon nanotubes with a grafted poly(4-vinylpyridine) linker

Multiwalled carbon nanotubes (MWCNTs) were grafted with poly(4-vinylpyridine) (PV4P) in aqueous solution by in situ free radical polymerization of 4-vinylpyridine. The as-prepared PV4P-g-MWCNTs hybrids can load phosphotungstic acid (PW) on a large scale by electrostatic interaction, which was characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The as-prepared PWs/PV4P-g-MWCNTs hybrids were modified onto a carbon glassy electrode. Cyclic voltammograms (CVs) show that the electrochemical behavior of the modified electrode follows a four-one-electron surface-confined process of Keggin-type PWs. The modified electrode can be used as a nitrite sensor. The comparison of CVs shows that the response current of nitrite reduction at the electrode modified with PWs/PV4P-g-MWCNTs hybrids is 15 times higher than that of PWs/MWCNTs hybrids in a control experiment at 0.65 V (vs. AgCl). The amperometric i–t curve for the electrode modified with PWs/PV4P-g-MWCNTs hybrids exhibits a linear concentration of ranged from 1.2 to 17.5 μM with a detection limit of 0.2 μM.     

Self-assembly and conductive network formation of vapor-grown carbon fiber in a poly(vinylidene fluoride) melt

The construction of vapor-grown carbon fiber (VGCF) conductive networks through the self-assembly process in a poly(vinylidene fluoride) (PVDF) melt was investigated. Depending on real-time tracing of the variation of electrical resistivity with isothermal treatment time, the properties and possible assembly mechanism of PVDF/VGCF composites were evaluated. It was found that the self-assembly velocity of VGCFs in the matrix increased with annealing temperature. Scanning electron microscopy showed that the coagulation of VGCFs formed the conductive paths in the matrix after annealing. The value for the activation energy of conductive network formation was about 144 kJ/mol, which was higher than the value for the activation energy of zero-shear-rate viscosity () of the pure polymer (62 kJ/mol), but was close to the value for the activation energy of of VGCF filled PVDF composites (135 kJ/mol). These results indicated that the conductive network of the composites was related to the interaction between PVDF molecules and VGCFs. According to a thermodynamic percolation model, a self-assembly velocity model for conductive network formation was proposed, and the result indicated that self-assembly velocity was a function of annealing time and temperature.     

Criteria dilemma of phase behavior in ternary blends comprising polystyrene, poly(alpha-methyl styrene), and poly(4-methyl styrene)

A ternary blend system of polystyrene (aPS), poly(α-methyl styrene) (PαMS), and poly(4-methyl styrene) (P4MS) (blends of three styrenic homopolymers of similar molecular structures) was investigated by using differential scanning calorimetry (DSC), polarized-light optical microscopy (POM), scanning electron microscopy (SEM), and solid-state ¹³C cross-polarization/magic angle spinning nuclear magnetic resonance (CP/MAS NMR). This ternary system of aPS/PαMS/P4MS exhibits a small miscibility loop only at relatively high percentages of PαMS (≥80%), while most of the aPS/PαMS/P4MS compositions exhibit two coexisting aPS/PαMS and aPS/P4MS phases in the immiscibility loop. In the immiscible loop, SEM measurements revealed evidence in contrasting with DSC for criteria of miscibility. DSC characterization revealed a single T_g for most ternary blend compositions; however, SEM graphs apparently indicated sub-micron phase domains, except for several PαMS-rich compositions (>80%). The and techniques using NMR were found to resolve the dilemma between the conventional thermal analysis and microscopy results, and indeed supported that the ternary blends at above 80% PαMS are completely homogeneous on the molecular level. Attempts have been made to resolve the seemingly contradictory interpretations on the complex ternary phase structures and domains from the DSC, and microscopy results.     

Aspirin particle formation by electric-field-assisted release of droplets

An aspirin solution flowing through a needle at () was subjected to an electric field of to generate droplets. The aspirin droplet size distribution generated was measured and is shown to be trimodal with the most significant size, . Deposited droplets and their aspirin crystal relics were also studied by electron microscopy. Immediately after deposition, the droplets were remarkably uniform in size and produced particulate crystals and were considerably more regular in morphology when compared with those formed without using an electric field.     

Morphological study on three kinds of two-dimensional spherulites of poly(butylene terephthalate) (PBT)

Three kinds of thin film specimens, each of which containing one of the three types of two-dimensional poly(butylene terephthalate) (PBT) spherulites (i: usual-positive type, ii: usual-negative type, and iii: unusual type), were prepared and studied mainly by transmission electron microscopy. It was confirmed that all these kinds of spherulites are made up of only the α-modification crystals, and the growth directions for usual-positive type, usual-negative type, and unusual type are the [010]^∗, ^∗, and ^∗ directions in the reciprocal lattice, respectively. Furthermore, the arrangement of unit cell in each type of the spherulites was determined. The relationships between the arrangements of unit cell and the types of each resulting spherulite are discussed.     

Poly(vinyl alcohol)-poly(acrylic acid) interpenetrating networks. Study on phase separation and molecular motions

We report on the preparation and characterization of interpenetrating polymer networks (IPNs) composed of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAAc) formed by a sequential method. Interpolymer interactions were examined using ¹³C CP/MAS NMR and DSC methods. Evidence on the formation of a PVA-PAAc complex through hydrogen bonds between the hydroxyl groups of the PVA chains and the carbonyl group of the PAAc chains was obtained. The existence of polymer interactions between PVA and PAAc and its effect on the molecular motion of polymer chains, was further investigated by means of the analysis of the ¹³C spin-lattice relaxation times in the rotating frame, . To elucidate the scale of the mixing in the PVA/PAAc IPNs, proton spin-lattice relaxation times in the rotating frame, , were also investigated. The analysis of the results reveals the compatibility between the PVA and the PAAc polymer networks at low PVA concentrations and the occurrence of phase separation at relatively high PVA concentrations.     

Comparison of poly(ethylene oxide) crystal orientations and crystallization behaviors in nano-confined cylinders constructed by a poly(ethylene oxide)-b-polystyrene diblock copolymer and a blend of poly(ethylene oxide)-b-polystyrene and polystyrene

A poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymer with a number average molecular weight of PEO blocks, =8.8 kg/mol, and a number average molecular weight of PS blocks, =24.5 kg/mol, (volume fraction of the PEO blocks, f_PEO, was 0.26) exhibited a hexagonal cylinder (HC) phase structure. Small angle X-ray scattering results showed that the PEO cylinder diameter was 13.3 nm, and the hexagonal lattice was a=25.1 nm. The cylinder diameter of this HC phase structure was virtually the same as that in the blend system constructed by a PEO-b-PS diblock copolymer (=8.7 kg/mol and =9.2 kg/mol) and a PS homo-polymer (=4.6 kg/mol) in which the f_PEO was 0.32. The cylinder diameter in this blend sample was 13.7 nm and the hexagonal lattice was a=23.1 nm. Comparing crystal orientation and crystallization behaviors of this PEO-b-PS copolymer with the blend, it was found that the crystal orientation change with respect to crystallization temperature was almost identical. This is attributed to the fact that in both cases the PEO block tethering densities and confinement sizes are very similar. This indicates that when the of PS homo-polymer is lower than the PS blocks, the PS homo-polymer is located inside of the PS matrix rather than at the interface between the PEO and PS in the HC phase structure. On the other hand, a substantial difference of crystallization behaviors was observed between these two samples. The PEO-b-PS copolymer exhibited much more retarded crystallization kinetics than that of the blend. Based on the small angle X-ray scattering results, it was found that in the blend sample, the HC phase structure was not as regularly ordered as that in the PEO-b-PS copolymer, and thus, the HC phase structure contained more defects in the blend. This led to a suggestion that the primary nucleation process in the confined crystallization is a defect-controlled process. The mean crystallite sizes were estimated by the Scherer equation, and the PEO crystal sizes are on the scale of the confined size.     

Dynamic rheological behavior and morphology near phase-separated region for a LCST-type of binary polymer blends

The dynamic rheological properties and morphology in the vicinity of phase-separated region for poly(methyl methacrylate) (PMMA)/poly(styrene-co-acrylonitrile) (SAN) blends with lower critical solution temperature (LCST) behavior were investigated. When temperature was above the phase separation temperature, i.e. cloud point (T_c) for some PMMA/SAN blends, the slope of plotting versus decreased at low frequencies (terminal region), indicating the appearance of phase-separation and existence of heterogeneous structure. We employed a model dealing with complex modulus of the two phases mixture proposed by Kopnistos et al. for describing the dynamic rheological behaviors of PMMA/SAN blends, according to the assumption that the interfacial tension between the matrix and the dispersed phase was independent of local shear and variation of interfacial area, and that the dispersed spherical droplets were nearly monodispersed. It is found that the predicted results were in qualitative agreement with the experimental data of this study. The ratio of interfacial tension α to the size of dispersed phase R, α/R, was obtained for 80/20 and 60/40 PMMA/SAN blends, and the two different morphology were also observed.     

Crystal structure identification of poly(trimethylene 2,6-naphthalate) β-form crystal by X-ray diffraction and molecular modeling

X-ray powder diffraction and molecular modeling are used to identify the crystal structure and chain conformation of poly(trimethylene 2,6-naphthalate) (PTN) β-form crystal. The unit cell of PTN β-form crystal was determined to be a triclinic with dimensions of α=100.85°, β=88.78° and γ=120.63°, and the space group of the crystal is identified as The observed crystal density of 1.37 g cm⁻³ and the determined dimensions of unit cell indicate that the unit cell contains one polymer chain with two repeating units. In the unit cell, each trimethylene unit in PTN backbone is in gauche/gauche conformation and neighboring naphthalene units are in face-to-face type arrangement, forming π-stacks that lead to the lowest energy of the unit cell.     

Macroscopic investigation of hydrate film growth at the hydrocarbon/water interface

Clathrate hydrate film growth has been investigated at the hydrocarbon/water interface for cyclopentane and methane hydrate, using video microscopy combined with gas consumption measurements. Hydrate formation was characterized by the film thickness, propagation rate across the hydrocarbon/water interface, and gas consumption. The film formation processes of cyclopentane and methane hydrate were measured over the temperature range of 260-273 K and pressure range of atmospheric to 8.3 MPa. Hydrate formation was initiated by the propagation of a thin, porous film across the hydrocarbon/water interface. This thickening rate was strongly dependent on the hydrate former solubility in the aqueous phase, in the absence and presence of hydrate. The methane hydrate film thickness began at about and grew to a final thickness (20-) which increased with subcooling. The cyclopentane hydrate film thickness began at about and grew to a final thickness (15-) which again increased with subcooling. The hydrate film grew into the water phase. Gas consumption indicated that the aqueous phase supplied hydrate former during the initial hydrate growth, and the free gas supplied the hydrate former for film thickening.     

Reverse microemulsion mediated sol-gel synthesis of lithium silicate nanoparticles under ambient conditions: Scope for CO2 sequestration

We report on the synthesis of nanocrystalline lithium silicate by coupling of sol-gel method in reverse microemulsion. The sample calcined at 800 °C gives pure phase lithium metasilicate nanocrystallites. X-ray diffraction and transmission electron microscopy confirmed the formation of nanocrystalline lithium silicate particles with a narrow size distribution. The nanoparticle prepared in the microemulsion shows enhanced CO₂ sorption capacity and shorter retention times at higher temperature ( at STP at 610 °C) which are better than the best known results.     

Labyrinthine pattern of polymer crystals from supercooled ultrathin films

We report the observation of a labyrinthine crystal pattern with a periodic structure in the crystal width direction in ultrathin films of poly(ethylene oxide) fractions with molecular weight ranging from 25,000 to 932,000 g/mol. The polymer thin films are crystallized at temperatures well below the bulk melting temperature, thus the system is characterized by limited diffusion of the polymer chains and rapid growth of the crystal fronts. The competition of these two competing factors leads to the formation of the labyrinthine pattern. This mechanism is supported by a scaling relation between the long period and molecular weight, , indicating the importance of chain diffusion. Furthermore, a linear relationship between and is observed, implying that the crystal growth is dominated by a secondary nucleation.     

The domain structure and mobility of semi-crystalline poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate): A solid-state NMR study

Solid-state NMR techniques have been employed to investigate the domain structure and mobility of the bacterial biopolymeric metabolites such as poly(3-hydroxybutyrate) (PHB) and its copolymers poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) containing 2.7 mol% (PHBV2.7) and 6.5 mol% (PHBV6.5) 3-hydroxyvalerate. Both single-pulse excitation with magic-angle spinning (SPEMAS) and cross-polarization magic-angle spinning (CPMAS) ¹³C NMR results showed that these biopolymers were composed of amorphous and crystalline regions having distinct molecular dynamics. Under magic-angle spinning, ¹H T_1ρ and ¹³C T₁ showed two processes for each carbon. Proton relaxation-induced spectral editing (PRISE) techniques allowed the neat separation of the ¹³C resonances in the crystalline regions from those in the amorphous ones. The proton spin-lattice relaxation time in the tilted rotating frame, , measured using the Lee-Goldburg sequence with frequency modulation (LGFM) as the spin-locking scheme, was also double exponential and significantly longer than ¹H T_1ρ. The difference between for the amorphous and crystalline domains was greater than that of ¹H T_1ρ. Our results showed that the differences could be exploited in LGFM-CPMAS experiments to separate the signals from two distinct regions. ¹H spin-diffusion results showed that the domain size of the mobile components in PHB, PHBV2.7 and PHBV6.5 were about 13, 24 and 36 nm whereas the ordered domain sizes were smaller than 76, 65 and 55 nm, respectively. The results indicated that the introduction of 3-hydroxyvalerate into PHB led to marked molecular mobility enhancement in the biopolymers.