Morphological changes towards enhancing piezoelectric properties of PVDF electrical generators using cellulose nanocrystals

For the first time, a nanocomposite of poly(vinylidene fluoride)/cellulose nanocrystal (PVDF/CNC) is developed as a piezoelectric energy harvester. This is implemented through electrospinning of PVDF solutions containing different levels of CNC loading, i.e., 0, 1, 3 and 5 % with respect to PVDF weight. Analytical techniques including DSC, FTIR and WAXD are conducted to monitor the polymorphism evolution within electrospun nanocomposites as the CNC content is varied. The results imply that CNCs at the optimum concentration (3 and 5 %) can effectively nucleate β crystalline phases. The nucleation of α crystalline phases is also prevented when CNCs are present within the structure of PVDF electrospun fibers. These changes in polymorphism give PVDF/CNC nanocomposites enhanced piezoelectric characteristics compared to pure PVDF nanofibers. We have demonstrated that the developed nanocomposites can charge a 33-μF capacitor over 6 V and light up a commercial LED for more than 30 s. It is envisaged that the PVDF/CNC nanocomposites provide the opportunity for the development of efficient electrical generators as self-powering devices to charge portable electronics.     

Ensemble evaluation of polydisperse nanocellulose dimensions: rheology,electron microscopy,X-ray scattering and turbidimetry

Six types of CNCs with different sizes were prepared from tunicins by sulfuric acid hydrolysis and subsequent sonication in water. The size distributions of CNCs were comprehensively evaluated by turbidimetry, small angle X-ray scattering, and microscopy to predict their intrinsic viscosities. Experimental intrinsic viscosities [η] of the CNC dispersions were evaluated by shear viscosity measurement, and then compared with their theoretical [η] values based on theories for rotational motions of rigid rods. The experimental [η] values for the straight CNCs were in good agreement with their theoretical [η] values, irrespective of the size and distributions. On the other hand, the experimental [η] value of the kinked CNC was higher than the theoretical [η] value, in agreement with a theoretical calculation giving higher intrinsic viscosities for bent fibers.     

The influence of chitin nanocrystals on structural evolution of ultra-high molecular weight polyethylene/chitin nanocrystal fibers in hot-drawing process

Ultra-high molecular weight polyethylene (UHMWPE)/chitin nanocrystal (CNC) fibers were prepared. Compared with the pure UHMWPE fibers, the ultimate tensile strength and Young’s modulus of UHMWPE/CNC fibers are improved by 15.7% and 49.6%, respectively, with the addition of chitin nanocrystals (CNCs) of 1 wt%. The melting temperature (T _m) of UHMWPE/CNC fibers was higher than that of pure UHMWPE fibers. Pure UHMWPE fibers and UHMWPE/CNC fibers were characterized with respect to crystallinity, orientation and kebab structure by wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM). It is found that the CNCs act as the shish structure in UHMWPE/CNC fibers and the kebab crystals are grown around the CNCs. There was almost no difference between pure UHMWPE fibers and UHMWPE/CNC fibers in orientation. But the degree of crystallinity of various stages of UHMWPE/CNC fibers was respectively higher than the corresponding stage of pure UHMWPE fibers. Moreover, the addition of 1 wt% CNCs improved the thickness of kebab crystals and accelerated the transformation of kebab to shish.     

Structure and dynamics of a free aquaporin (AQP1) by a coarse-grained Monte Carlo simulation

Structure and dynamics of a free aquaporin (AQP1) are studied by a coarse-grained Monte Carlo simulation as a function of temperature using a phenomenological potential with the input of a knowledge-based residue–residue interaction. Response of the radius of gyration (R _g) of the protein to the temperature (T) is found to be nonlinear: Decay of R _g at T ≤ T _c is followed by a continuous increase at T ≥ T _c before reaching its saturation. In thermo-responsive regime, the protein exhibits segmental globularization with the persistence of three regions along its sequence involving residues ¹M–²⁵V and ²⁵⁰V–²⁶⁹K toward the beginning and end segments with a narrow intermediate region around ¹⁵⁵A–¹⁶³D. A detail analysis of the structure factor S(q) shows a global random coil conformation at high temperatures with an effective dimension D _e ~ 1.74 and a globular structure (D _e ~ 3) at low temperatures. In thermo-responsive regime, the variation of S(q) with the wave vector q reveals a systematic redistribution of self-organizing residues (in globular and fibrous sections) that depends on the length scale and the temperature.     

Spatial structure of water over the whole region of short-range ordering

A new approach to spatial analysis of molecular arrangement over the whole region of short-range ordering is suggested. The structural properties of water are calculated by the Monte-Carlo method using the SPC/E intermolecular interaction potential. Structural correlations are considered at distances of up to 10 Å. The functions g _OO, g _OH, and g _HH, and the partial functions corresponding to different local densities of surroundings and different coordination numbers of water molecules have been obtained. An analytical procedure has been developed to find the spatial distribution of particles, and the total and partial functions have been determined for particles of the same (having identical c.n.₁ and c.n.₂) and different types. The functions are considered for layers R _min < R < R _max corresponding to different coordination spheres of water molecules (up to 10 Å). A structural model of water is suggested, in which the deviation of the 3D net of H bonds from tetrahedricity is associated with the formation of configurations complementary to icelike configurations of water. The model is supported by the results of computer simulation.     

Molecular dynamics simulations of the characteristics of sodium carboxymethyl cellulose with different degrees of substitution in a salt solution

Sodium carboxymethyl cellulose (SCMC) with different degrees of substitution (DS) possesses structural characteristics and physicochemical properties that are important in broad areas of industrial applications. This reported work investigated the structural characteristics, including the effective length (L _ef), the radius of gyration (R _g), and the hydrodynamic radius (R _H), and the physicochemical properties, including intrinsic viscosity ([η]) and salt tolerance, of SCMC with a DS more than 1.0 in NaCl solution using molecular dynamics (MD) simulations. In the MD simulations, the DS of SCMC varied from 1.2 to 2.8, and the NaCl concentration varied from 0 to 1.4 mol/L. MD simulation results showed that with the increment of NaCl concentration, the L _ef (or R _g or R _H) of SCMC decreased; with the increment of the DS, the L _ef of SCMC increased. Also, the variation tendency of [η] in the NaCl solution was consistent with its L _ef (or R _g or R _H). It was noted that the salt tolerance (represented by D) of SCMC increased as the DS increased. In addition, the sharp variation of the D value of SCMC occurred in the range of DS of 1.6 to 2.0, which agreed with the reported experimental results. Radial distribution function analyses showed that the Na⁺ cations had a stronger interaction with the carboxyl groups in SCMC with lower DS when it was present in a salt solution of higher concentration, which also reasonably explained the variation of L _ef, R _g, R _H, [η], and D of SCMC in NaCl solution.     

Poly(ε-caprolactone) (PCL)/cellulose nano-crystal (CNC) nanocomposites and foams

Poly(ε-caprolactone) (PCL)/cellulose nanocrystal (CNC) nanocomposites were produced via twin-screw extrusion. Microcellular nanocomposite samples were produced with microcellular injection molding using carbon dioxide (CO₂) as physical blowing agent. The foaming behavior, physical properties, thermal properties, crystallization behavior, and biocompatibility were investigated. It was found that the CNCs interacted with the PCL matrix which led to a strong interface. The CNCs effectively acted as nucleation agents in microcellular injection molding. Both solid and foamed samples with higher levels of CNC content showed higher tensile moduli, complex viscosities, and storage moduli due to the reinforcement effects of CNCs. Furthermore, improvement in the foamed samples was more significant due to their fine cell structure. The addition of CNCs caused a reduction of the decomposition temperature and an increase in the glass transition temperature, crystallization temperature, and crystallinity of PCL. Moreover, the biocompatibility of the foamed nanocomposites with low CNC content was verified by 3T3 fibroblast cell culture.     

Preparation and Properties of Hybrid Nanostructures of Zinc Tetraphenylporphyrinate and an Amphiphilic Copolymer of <Emphasis Type="Italic">N</Emphasis>-Vinylpyrrolidone in a Neutral Aqueous Buffer Solution

Water-soluble forms of a hydrophobic dye, zinc tetraphenylporphyrinate, are obtained via its solubilization by polymer particles of the micellar type formed by a copolymer of N-vinylpyrrolidone with triethylene glycol dimethacrylate. Hydrodynamic radii R_h and the size distribution of such particles in neutral aqueous buffer solutions are determined via dynamic light scattering. The electrochemical activity of the encapsulated dye is found, and its photochemical properties (absorption and fluorescence) are studied.     

Noncovalent columnar structures based on β-cyclodextrin

A new method for the synthesis of associates of cyclodextrins (CDs) of the columnar type consisting of the precipitation of CDs from aqueous solutions into acetone at lowered temperatures is developed. It is shown that columnar structures exist in both a crystalline state and in aqueous solutions. Hydrodynamic radii and molecular masses of noncovalent columnar structures (NCSs) in aqueous solutions are determined by the dynamic and static light scattering methods. The degree of association of noncovalent columnar polymers is ～40. It is revealed the NCS associates based on β-CD are stable and their hydrodynamic radius R _h is equal to 100 ± 10 nm. The kinetics of interactions of initial β-CD and NCS with poly(propylene oxide) (PPO) is studied. The pattern of kinetic curves of R _h growth upon interaction between NCS and PPO indicates that the aggregation of the particles of polymer inclusion complex proceeds in the regime of reaction-limited cluster-cluster aggregation. Kinetic curves describing the interaction processes between β-cyclodextrin and PPO are characterized by the presence of induction period t ₀. At t > t ₀, R _h ∞ t ^0.56 which is typical for the diffusion-limited cluster-cluster aggregation. Schemes of the formation of polymer inclusion complexes between initial β-CD or NCS and poly(propylene oxide) are proposed. Comparison of kinetic data on the complexation of β-CD in solution in the form of associates of two types with PPO demonstrates that columnar forms of associates are reactive species acting as macroreceptors.     

Peculiarities of molecular light scattering in a chlorobenzene—<Emphasis Type="Italic">o</Emphasis>-dichlorobenzene system and their relationship to the solution structure

The general coefficient of molecular light scattering (R ₀), degree of depolarization (ΔU), and refractive index (n) in a system of o-dichlorobenzene—chlorobenzene solutions were measured. The anisotropic (R _a) and isotropic (R _is) contributions to scattering and the iso-thermal compressibility and its excess component were calculated. A complicated nonmono-tonic behavior was found for the concentration dependences of the coefficients of molecular light scattering with a minimum in a range of low concentrations from the side of chlorobenz-ene and a maximum from the side of o-dichlorobenzene, indicating a substantial rearrange-ment of the structure of the solutions with a change in the concentration. An analysis of the concentration dependences of the coefficients of molecular light scattering, excess isother-mal compressibility, and excess molar volume revealed four ranges differed in structure: 0—0.03, 0.03—0.65, 0.65—0.9, and 0.9—1.0. The solution structure was described in each range.     

Non-Isothermal Crystallization of Poly (vinylidene fluoride)/Poly (methyl methacrylate)/Cellulose Nanocrystal Nanocomposites

Poly (vinylidiene fluoride) (PVDF)/poly (methyl methacrylate) (PMMA)/cellulose nanocrystal (CNC) nanocomposites were prepared by solution blending. Non-isothermal crystallization of PVDF/PMMA (70/30) blend and its composites was investigated using differential scanning calorimetry. It was found that the addition of CNCs played a positive role in both the crystallization rate and crystallization percentage. The addition of CNCs increased the initial crystallization temperature, peak crystallization temperature, and crystalline enthalpy. The Avrami index indicated that CNCs did not change the crystallization mechanism; while other parameters derived from Jeziorny theory and Mo's method, including Z _c , F(t), and α, further verified the positive role played by CNCs.     

Adjustable crystalline stereocomplexes from enantiopure gradient polycarbonates

Stereoselective interaction was observed in the mixture of enantiopure gradient polycarbonate (denoted as PCOPC-g-PCPC, originated from the enantioselective terpolymerization of CO₂, 3,4-epoxytetrahydrofuran (COPO) and cyclopentene oxide (CPO)) and various isotactic polycarbonates with opposite configuration in chloroform solution. The resultant crystalline stereocomplexes exhibit enhanced thermal stability and new crystalline behaviors, significantly distinct from their parent polymers. It was found that the cocrystallization selectively occurred between (R)-PCOPC (CO₂/COPO copolymer) and (S)-PCOPC-enriched segment in the gradient terpolymer (S)-PCOPC-g-PCPC, while (R)-PCPC (CO₂/CPO copolymer) selectively complexed with (S)-PCPC-enriched segment. No stereocomplexation was observed between (S)-PCOPC-g-PCPC and (S)-PCOPC or (S)-PCPC. This study is beneficial to finding new routes to prepare various semicrystalline materials having a wide variety of physical properties and degradability.     

Hierarchical nanocomposites of polyaniline scales coated on graphene oxide sheets for enhanced supercapacitors

The homogeneous polyaniline–graphene oxide (PANI-GO) nanocomposites were facilely assembled with a redox system in which cumene hydroperoxide (CHP) and iron dichloride (FeCl₂) acted as oxidant and reductant, respectively. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed that PANI scales coated uniformly on the surface of GO sheets owing to the synergistic effect between the PANI and GO. The obtained PANI-GO nanocomposites exhibited improved electrochemical performance as an electrode material for supercapacitors compared with the pure PANI. The specific capacitance of the PANI-GO nanocomposites was high up to 308.3 F g^?1, much higher than that of the pure PANI with specific capacitance of 150 F g^?1 at a current density of 1 A g^?1 in 2 M H₂SO₄ electrolyte. The Raman and XPS results illustrated that enhanced electrochemical performance might be attributed to the π-π conjugation between the PANI and GO sheets.     

Studies on the <Emphasis Type="Italic">g</Emphasis>-factors of the copper(II)–oxygen compounds

The g factors for Cu²⁺ in meta-zeunerite (Cu(UO₂)₂(AsO₄)₂·3H₂O), kroehnkite (Na₂Cu(SO₄)₂·2H₂O), copper benzoate (Cu(PhCO₂)₂·3H₂O) and diaboleite (Pb₂Cu(OH)₄Cl₂) of the tetragonal phase are uniformly treated by high order perturbation formulas for 3d ⁹ ions in tetragonally elongated octahedra. The calculation results are in good agreement with the observed values and systematically analyzed in view of the local structures around Cu²⁺. The g anisotropies Δg (= g _‖?g _⊥) are largely ascribed to the local tetragonal elongations of the Cu²⁺ sites, characterized by the relative elongation ratios (R _‖?R _⊥)/R? ≈ 19%, 21%, 27% and 30% for metazeunertie, kroehnkite, copper benzoate and diaboletie, respectively. The anomalous valley (minimum) of relative g anisotropy for copper benzoate is attributed to the modification of the Cu²⁺ electronic states due to the phenyl ring. The ligand orbital contributions are found to be significant due to covalency, and should be taken into account. The present study would be helpful to the unified investigations of structures and properties of the copper oxygen compounds.     

Extinction coefficients of gold nanoparticles and their dimers. Dependence of optical factor on particle size

The generalized Mie theory has been employed to calculate extinction coefficients κ for isolated gold nanoparticles of different sizes (4–80 nm) and their dimers (κ₂) at the maximum of the short-wave plasmon resonance band. It has been found that the value of κ₂ essentially depends on both interparticle distance s and particle sizes R. According to the character of variations in the κ₂(s) dependence, three ranges of the distances are distinguished, i.e., large, intermediate, and small. In the first range, the κ₂ values slightly differ from doubled κ values. Nevertheless a tendency toward an increase in κ₂ is distinctly seen as the particles approach each other, and, within some range of s values and for particles with radii R < 15 nm, κ₂ is higher than 2κ. For dimers of larger particles, κ₂ < 2κ, with its value gradually decreasing with a reduction in the s value. The behavior changes when the particle sizes are of about 50 nm. In the range of small interparticle distances, κ₂ values slightly vary with the distance between the particles somewhat decreasing or oscillating with a small amplitude about some mean value. In this range, as the sizes of the gold particles grow, the extinction coefficients of dimers increasingly deviate from the sum of the extinction coefficients of the particles composing the dimers. For 20–80 nm nanoparticles, the size-dependence plotted for the extinction efficiency of dimers in logarithmic coordinates within the range of small interparticle distances is described by a straight line, the slope of which (1.036 ± 0.039) appears to be somewhat smaller than the slope of a corresponding line for individual gold particles (1.274 ± 0.014). The ratio between κ₂ and κ predetermines the character of variations in the optical factor as depending on the particle size and the interparticle distance and governs the behavior of the sol turbidity at the stage of nanoparticle dimerization.     

Density,Viscosity, and Glass Transition of an Ethylenediamine–Ethylene Glycol Binary System

Densities ρ and viscosities η were measured for the binary mixtures of ethylenediamine (EDA) and ethylene glycol (EG) in the temperature range 288.15–323.15 K for ρ and at 273.15–323.15 K for η, both of which are broader temperature ranges than those reported previously. The value of ρ monotonously decreases against the mole fraction of EDA, x _EDA, and increasing temperature. The concentration dependence of η exhibits a maximum in the intermediate concentration range at all temperatures measured. The glass transition temperature, T _g, for samples with x _EDA < 0.7 was measured using differential scanning calorimetry. The measured T _g values show a peak in the intermediate concentration range, which is a behavior similar to that of η; however, the peak concentrations for η and T _g did not precisely align because of a deviation in the maximum hydrogen-bond density. The partial molar volumes for EDA and EG and the thermal expansivities, α, were obtained from ρ. Results in the present study are discussed in terms of the extensively increasing hydrogen-bond density for polyamine–polyhydric alcohol systems.     

Electron diffraction study of molecular structure of mebicar

The structure of the mebicar molecule has been studied by gas-phase electron-diffractometry using quantum chemical calculations. An eclipsed conformation along the C-C bond (torsion angle ?(H-C-C-H) = 10°) and flattened semi-chair conformations of cyclic fragments have been found. The bond lengths (r _g ) and angles (∠α) show the following average values: r(C-C) 1.576(3) Å, r(C-N) 1.460(3) Å, r(C(O)-N) 1.390(4) Å, r(C=O) 1.211(5) Å, r(C-H) 1.090(5) Å, ∠CCN 103.0(5)°, ∠CNC(O) 112.2(1)°, ∠CNC 122.4(1)°. The dihedral angle between the cyclic fragments is 116.6°.     

A study of structural non-stoichiometry with respect to oxygen in <Emphasis Type="Italic">R</Emphasis>BaCo<Subscript>4</Subscript>O<Subscript>7+<Emphasis Type="Italic">x</Emphasis></Subscript> single crystals

Impurity-free RBaCo₄O_7+x (R = Y, Lu) crystals are grown and the evolution of their structure with varying oxygen concentration in the range 0 ≤ x ≤ 1.3 is studied. The structural features of the studied samples required to develop an extended strategy of the X-ray crystallographic experiment, which made it possible to obtain more accurate data on unit cell parameters and additional information on the features of superstructure modulation and diffuse scattering, along with the phase composition of crystalline samples. A crystal chemical analysis of the known structural models of RBaCo₄O_7+x is performed and suggestions are made about possible structural changes occurring when the oxygen concentration increases up to the limit.     

表面官能团化增强碳纳米笼超级电容器性能

以具有多级孔结构、高比表面积、良好导电性等特征的碳纳米笼（CNCs）为前体,采用硝酸氧化法在CNCs表面引入含氧官能团。以CNCs为超级电容器电极材料,在相同电流密度下,官能团化样品的比电容显著高于纯CNCs;在1A·g^-1下比电容最高可达到255F·g^-1,比纯CNCs的188F·g^-1增加了34%,这表明表面含氧官能团化能够显著提高CNCs的超级电容器比电容。在100A·g^-1的大电流密度下,硝酸氧化后CNCs的比电容保持在111~167F·g^-1,表明具有良好的耐大电流充放电性能。在10A·g^-1的电流密度下循环10000圈后,CNC-6M样品的比电容由196F·g^-1下降到176F·g^-1,样品的比电容仍保留90%,具有良好的循环稳定性。表面含氧官能团化CNCs所表现出的这种优异的超级电容器性能归因于CNCs的多尺度分级孔结构、高比表面积、良好的导电性、表面亲水性含氧官能团化带来的浸润性提高和引入的赝电容。     

Glass formation in systems of mercury,cesium, and lead bromides

The results of studies of glass formation in the binary subsystems of the ternary system HgBr₂-PbBr₂-CsBr and in several samples whose compositions lie near ternary eutectic points of the indicated ternary systems are reported. The conditions for glass formation have been determined. The characteristic temperatures have been determined by DTA, and T _g /T _m ratios and H _R factors for glassy samples calculated.