Physical and mechanical properties of poly(methyl methacrylate) -functionalized graphene/poly(vinylidine fluoride) nanocomposites: Piezoelectric β polymorph formation

Poly(methyl methacrylate) -functionalized graphene (MG) is prepared from graphene oxide (GO), using atom transfer radical polymerization (ATRP) and reducing with hydrazine hydrate. PMMA causes an increase of height of MG sheet for polymerization of MMA at side and basal planes. MG layers become thinner for exfoliation during composite formation. Graphene sheets enhance piezoelectric β-polymorph PVDF formation. MG sheets nucleate PVDF crystals and a gradual decrease of α phase occurs with a concomitant rise of β phase. Thermal stability of nanocomposites increases significantly and the T_g increase is really large (21 °C). Storage modulus shows an increase of 124%, stress at break 157% and Young’s modulus 321% for 5% MG. Parallel orientation of graphene sheets changes to random orientation for high graphene content. It exhibits conducting percolation threshold at 3.8% MG and variable range hopping model suggests that conductivity is contributed from the intergrain tunnelling and hopping between the grains.     

Oxidative degradation of poly (vinyl acetate) and poly (ε-caprolactone) and their mixtures in solution

The oxidative degradation of the poly (ε-caprolactone) (PCL), poly (vinyl acetate) (PVAC) and their mixtures in dichlorobenzene has been investigated at various temperatures (70-130°C) in the presence of benzoyl peroxide. The interaction between the polymers is quantified by monitoring the molecular weights of individual polymers using gel-permeation chromatography. The various physical mixtures employed in the present investigation are , and wt%/wt% PCL/PVAC. Experimental data indicated that the degradation is random without cross-linking and repolymerization. An optimum in degradation temperature (corresponding to maximum degradation rate) of 105°C was observed for the entire range of polymer compositions (0-100% PCL) investigated. This optimum temperature of degradation is characteristic mostly of the initiator and only to a small extent of the degrading polymer system. The experimental results of the mixtures indicated that the degradation rates of PVAC are significantly enhanced, while the degradation rates of PCL are decreased in the physical mixture. This can be attributed to the proton-accepting and proton-donating nature of PCL and PVAC, respectively. A radical mechanism for the oxidative degradation of pure polymers and their mixtures has been proposed and a model based on continuous distribution kinetics was developed considering the interaction of the polymers through hydrogen abstraction and the parameters were evaluated numerically. The activation energies for the peroxide attack for the PCL and PVAC are 10.5 and , respectively. The activation energies for the random chain scission of PCL and PVAC are 10.6 and , respectively.     

Three-liquid-phase extraction and separation of V(V) and Cr(VI) from acidic leach solutions of high-chromium vanadium–titanium magnetite

A new method by liquid–liquid–liquid three phase system, consisting of acidified primary amine N1923(abbreviated as A-N1923), poly(ethylene glycol)(PEG) and (NH_4)_2SO_4 aqueous solution, was suggested for the separation and simultaneous extraction of V(V) and Cr(VI) from the acidic leach solutions of highchromium vanadium–titanium magnetite. Experimental results indicated that V(V) and Cr(VI) could be selectively enriched into the A-N1923 organic top phase and PEG-rich middle phase, respectively, while Al(III)and other co-existing impurity ions, such as Si(IV), Fe(III), Ti(IV), Mg(II) and Ca(II) in acidic leach solutions,could be enriched in the(NH_4)_2SO_4 bottom aqueous phase. During the process for extraction and separation of V(V) and Cr(VI), almost all of impurity ions could be removed. The separation factors between V(V) and Cr(VI) could reach 630 and 908, respectively in the organic top phase and PEG middle phase, and yields of recovered V(V) and Cr(VI) in the top phase and middle phase respectively were all above 90%.Various effects including aqueous p H, A-N1923 concentration, PEG added amount and(NH_4)_2SO_4 concentration on three-phase partitioning of V(V) and Cr(VI) were discussed. It was found that the partition of Cr(VI) into the PEG-rich middle phase was driven by hydrophobic interaction, while extraction of V(V) by A-N1923 resulted of anion exchange between NO_3~- and H_2V_(10)O_(28)~(-4). Stripping of V(V) and Cr(VI) from the top organic phase and the middle PEG-rich phase were achieved by mixing respectively with NaNO_3 aqueous solutions and Na OH-((NH_4)_2SO_4 solutions. The present work highlights a new approach for the extraction and purification of V and Cr from the complex multi-metal co-existing acidic leach solutions of high-chromium vanadium–titanium magnetite.     

A facile and low-cost preparation of durable amphiphobic coatings with fluoride–silica@poly(methacrylic acid) hybrid nanocomposites

Poor robustness, high cost and complicated preparation are the main barriers to the large-scale industrial application of amphiphobic coatings. A facile and low-cost method to fabricate durable amphiphobic coatings is reported in this work. The coatings were composed of top and bottom paints. The top paint was prepared by the F–Si@PMAA hybrid nanocomposites dispersion. The hybrid nanocomposites with dual structure were prepared via the co-condensation reaction of tetraethoxysilane (TEOS) and 1H,1H,2H,2H-Perfluorodecyl triethoxysilane (HDFTES) on the surface of the presynthesized PMAA nanoparticles in ethanol dispersion. The bottom one was a type of inexpensive car refinishing paint. The resulting coatings could be sprayed onto different substrates. All the coated substrates exhibited good amphiphobicity with superhydrophobicity with the water contact angle greater than 150°, water roll-off angle less than 4°, and high oleophobicity with the oil contact angle greater than 130°. Moreover, all of the prepared coatings exhibited great robustness after water jetting, sand abrasion, and knife scratching. This method can be an effective strategy for fabricating amphiphobic surfaces for practical industrial applications.     

Synthesis and characterization of a novel graft copolymer with poly(n-octylallene-co-styrene) backbone and poly(?-caprolactone) side chain

A novel graft copolymer consisting of poly(n-octylallene-co-styrene) (PALST) as backbone and poly(?-caprolactone) (PCL) as side chains was synthesized with the combination of coordination copolymerization of n-octylallene and styrene and the ring-opening polymerization (ROP) of ?-caprolactone. Poly(n-octylallene-co-styrene) (PALST) backbone was prepared from the copolymerization of n-octylallene and styrene with high yield by using the coordination catalyst system composed of bis[N,N-(3,5-di-tert-butylsalicylidene)anilinato]titanium(IV) dichloride (Ti(Salen)₂Cl₂) and tri-isobutyl aluminum(Al(i-Bu)₃). The molar ratio of each segment in the copolymer, and the molecular weight of the copolymer as well as the microstructure of the copolymer could be adjusted by varying the feeding ratio of both styrene and n-octylallene. The hydroxyl functionalized copolymer PALST-OH was prepared by the reaction of mercaptoethanol with the pendant double bond of PALST in the presence of radical initiator azobisisbutyronitrile (AIBN). The target graft copolymer [poly(n-octylallene-co-styrene)-g-polycaprolactone] (PALST-g-PCL) was synthesized through a grafting-from strategy via the ring-opening polymerization using PALST-OH as macroinitiator and Sn(Oct)₂ as catalyst. Structures of resulting copolymer were characterized by means of gel permeation chromatography (GPC) with multi-angle laser light scattering (MALLS), ¹³C NMR, ¹H NMR, DSC, polarized optical microscope (POM) and contact angle measurements.     

Helix-helix transition of poly(β-phenylpropyl l-aspartate) embedded in stable helical poly(γ-phenylethyl glutamate) matrix

We studied the helix-helix transition of poly(β-phenylpropyl l-aspartate) (3PLA) embedded in a right-handed α-helical (α_R) poly(γ-phenylethyl l-glutamate) (2PLG) or left-handed α-helical poly(γ-phenylethyl d-glutamate) (2PDG) matrix. Binary mixtures were prepared with 3PLA:2PLG (2PDG) mole fractions of 9:1 to 1:9. In all these mixtures, the 3PLA molecule exhibited helical sense inversion even if dispersed or isolated into the hard-rod matrix, and the inversion rate of the embedded 3PLA molecule was relatively higher than that of the pure system. Thus, it was concluded that the transition occurs in only a limited space and more easily for the isolated molecule. Further, the 3PLA molecule recognized the chiral environment produced by the surrounding polymers. For 3PLA surrounded by a 2PDG matrix, the helix-helix transition temperature was lower and the transition rate on cooling was slower than those for 3PLA surrounded by a 2PLG matrix. This is reasonable since the left-handed matrix helps right-handed to left-handed helical inversion.     

Poly(ε-caprolactone)-block-poly(N-vinyl pyrrolidone) diblock copolymers grafted from macrocyclic oligomeric silsesquioxane

Poly(ε-caprolactone)-block-poly(N-vinyl pyrrolidone) diblock copolymers grafted from macrocyclic oligomeric silsesquioxane (MOSS) (denoted MOSS[PCL-b-PVPy]₁₂) were synthesized via the sequential polymerizations involving ring-opening polymerization (ROP) of ε-caprolactone (CL) and RAFT/MADIX polymerization of N-vinyl pyrrolidone (NVP). The organic-inorganic brush-like diblock copolymers were characterized by means of nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC). Small angle X-ray scattering (SAXS) showed that all the MOSS[PCL-b-PVPy]₁₂ was microphase-separated in the amorphous state. The microphase-separated morphologies were quite dependent on the length of PVPy blocks and the crystallization behavior of PCL subchains was significantly affected by the lengths of PVPy subchains. In aqueous solutions, the MOSS[PCL-b-PVPy]₁₂ can be self-assembled into the polymeric micelles as evidenced by dynamic light scattering (DLS) and transmission election microscopy (TEM). The critical micelle concentrations of the brush-like diblock copolymers increased with increasing the lengths of PVPy blocks. It is proposed that the stability of the micellar cores was increased with the macrocyclic molecular brush structure of the diblock copolymers and the formation of the MOSS aggregates via MOSS–MOSS interactions.     

Stabilized β-Bi2O3 nanoparticles from (BiO)4CO3(OH)2 precursor and their photocatalytic properties under blue light

Stabilized tetragonal Bi₂O₃ nanoparticles (β-Bi₂O₃) were obtained by annealing treatments of amorphous Bi-based precursors, obtained by chemical precipitations, at temperatures between 350 and 450?°C. The formation of the stabilized β-Bi₂O₃ phase was possible by using (BiO)₄CO₃(OH)₂ while other precursors such as amorphous bismuth carbonate ((BiO)₂CO₃) and amorphous basic bismuth nitrate (Bi₆O₆(OH)₂(NO₃)₄·2H₂O) led to the formation of the thermodynamically stable monoclinic α-Bi₂O₃ and Bi₅O₇NO₃ phases. The Bi-based precursors were prepared by the chemical precipitation method at room temperature in ethylenediamine-solvent varying the HNO₃/Bi³⁺ molar ratio (10, 26 and 56). The physicochemical properties of the three as-prepared amorphous precursors and the formed-after-calcination β-Bi₂O₃, α-Bi₂O₃ and Bi₅O₇NO₃ phases were analyzed by X-ray diffraction, scanning electron microscopy, thermogravimetry, X-ray photoelectron spectroscopy (XPS), FTIR analysis, diffuse reflectance spectroscopy and surface area by BET method. The photocatalytic activity of all annealed solids containing the β-Bi₂O₃ phase was tested in the photodegradation of the indigo carmine (IC) dye under specific blue light. A schematic diagram of the Bi₂O₃ phases obtained as a function of the annealing conditions and initial amorphous precursor is proposed and explained in terms of the amount of CO₃^2-, NO₃^- and amine (ENH₂²⁺ ? ENH⁺) ions present in each bismuth precursor.     

Crystal structure and disorder in Poly(l-lactic acid) δ form (α′ form) and the phase transition mechanism to the ordered α form

Crystal structure of poly(l-lactic acid) (PLLA) α′ form (or the newly-termed “δ” form) has been analyzed on the basis of the X-ray diffraction data. The oriented δ form was obtained by stretching and annealing the melt-quenched sample at ca. 100 °C. The unit cell parameters were a = 10.80 Å, b = 6.20 Å, c (fiber axis) = 28.80 Å and α = β = γ = 90°. As seen from the lack of even-numbered 00l reflections (002, 004, ..) except the 0010 reflection, the chain conformation of the δ form was found to be more remarkably disordered than that of the regular α form. As already reported, the α form takes the (10/3) helix with approximately 2₁ screw symmetry although, more strictly speaking, this screw symmetry is not actually existent. The δ form does not possess any symmetry along the chain axis although the local torsional angles are not very much different from each other. As for the chain packing structure, the two different possibilities were assumed in the structural refinement procedure: (i) the corner and center chains direct upward and downward along the chain axis, respectively, just like the case of regular α form (alternate packing mode) and (ii) the upward and downward chains are located at the same lattice site at 50% probability (statistically-disordered packing mode). The structure analysis using the Bragg reflections suggested the preferability of the model (i). The diffuse and streaky lines were observed along the layer lines, originating from the relative-height disorder between the neighboring chains in the δ form. The X-ray diffuse scatterings coming from the various types of the disordered structure have been simulated, among which the disordered multi-domain structure model was found to be the most plausible model, where the domains constructed by the alternate arrangement of upward and downward chains are gathered together with the mismatch in the relative height between the neighboring domains. In this way the disorder-to-order phase transition from the δ to α form was found to occur through the conformational ordering of the chains accompanied with the chain packing regularization as well as the matching of the neighboring domain height to give a large single domain of the α form.     

The effect of [(η-C3H5)(η-C5H5)Mo(CO)2] on drying of solvent-borne alkyd paints

Allyl molybdenum complex [(η³-C₃H₅)(η⁵-C₅H₅)Mo(CO)₂] (Mo-A) was examined as a new drier for solvent-borne alkyd binder. The drying activity of pure Mo-A and the of combinations of Mo-A with cobalt(II) 2-ethylhexanoate (Co-Nuodex) was examined using standard methods for measurements of the drying time and hardness development of the alkyd film. The detailed study of the drying process was studied by time-resolved infrared spectroscopy on ethyl linoleate as well as on thin coating of alkyd binder.     

Synthesis and controlled release of curcumin-β-cyclodextrin inclusion complex from nanocomposite poly(N-isopropylacrylamide/sodium alginate) hydrogels

Inclusion complex of curcumin with β-cyclodextrin (Cur-β-CD) was prepared using coprecipitation method. Stoichiometric ratio between curcumin and β-cyclodextrin was found to be 1:2 with an association constant of 3.80 × 10⁸ M⁻² using Benesi–Hildebrand method. Inclusion complex formation was confirmed by FTIR and DSC analyses. Water solubility of curcumin increased from 0.00122 to 0.721 mg mL⁻¹ with the inclusion complex formation. Release of the inclusion complex from the nanocomposite and conventional poly(N-isopropylacrylamide/sodium alginate hydrogels crosslinked by nanoclay and N,N′-methylenebis(acrylamide) (BIS), respectively, were investigated in simulated gastrointestinal conditions. Swelling ratio and cumulative release were dependent on the hydrogel composition and pH. At pH = 1.2, hydrogels showed the lowest release ratio, but at pH = 6.8 highest swelling ratios were attained. The swelling ratio and cumulative release decreased with increasing the nanoclay content in nanocomposite hydrogels. On the contrary, as the ratio of BIS in the conventional hydrogels increased, the swelling ratio and cumulative release increased. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47554.     

Non-enzymatic and enzymatic degradation of poly(ethylene glycol)-b-poly(?-caprolactone) diblock copolymer micelles in aqueous solution

The non-enzymatic and enzymatic degradation behaviors of the monomethoxy-poly(ethylene glycol)-b-poly(?-caprolactone) diblock copolymers (MPEG-PCL) micelles in aqueous solution were investigated by DLS, ¹H NMR, SEC and HPLC. It is found that the degradation mechanism of MPEG-PCL micelles in aqueous solution in non-enzymatic case is quite different from that in the presence of enzyme. In non-enzymatic case, the degradation induced by acidic catalysis was not found in low pH aqueous solution but the degradation of the micelles occurred under neutral and basic conditions. The degradation of MPEG-PCL micelles first happens near the interface region of the MPEG shell and PCL core, leading to the part detachment of PEG chains. With increasing degradation time, the degradation inside the PCL core with a random scission on PCL chains occurred. Compared with non-enzymatic degradation, the enzymatic degradation of MPEG-PCL micelles is much fast and the degradation rate of MPEG-PCL micelles is proportional to either the micelles or the enzyme concentration in a certain range. Based on the micelle degradation behaviors that we observed, a possible mechanism for the enzymatic degradation of the MPEG-b-PCL micelles including PCL core erosion which results in cavitization of micellar core and micellar dissociation is proposed.     

Electroless-plating of Ag nanoparticles on Al2O3 and graphene Nano sheets (GNs) for improved wettability and properties of Al–Al2O3/GNs nanocomposites

Low wettability between reinforcements and matrix is a key challenge in the production of metal matrix nanocomposites with improved properties. In this paper, we employed electroplating technology to coat Al₂O₃ and Graphene Nano sheets (GNs) with Ag nanoparticles to improve their wettability with Al matrix. After coating, we used mechanical milling and sintering to manufacture Al–10%Al₂O₃/GNs hybrid nanocomposites with different GNs content. For all the manufactured composites, we evaluated the structural, mechanical and wear behaviors. The results revealed the efficiency of electroplating process for improving wettability between composite components resulting in very dense samples even for samples with relatively high GNs content. This improved wettability enable the production of hybrid composite with 2 times larger hardness and reduced wear rates due to the improved surface characteristics of Al₂O₃ and GNs nanoparticles caused by Ag plating over their surfaces. In comparison with available techniques and results in the literature, we achieved hybrid nanocomposite with 1.85 times larger hardness than the available Al-GNs nanocomposite and 1.75 times larger hardness than the available Al–Al₂O₃/GNs nanocomposites.     

The effects of doped Nd on conductivity and phase stability of BaCe0.8Y0.2O3−δ-based electrolyte for solid oxide fuel cell

This study investigates the structure, phase stability, and electrical properties of BaCe_0.8Y_0.2−xNd_xO_3−δ (x = 0-0.2) in humid air. XRD results indicate that a BaCe_0.8Y_0.2−xNd_xO_3−δ sample has an asymmetric orthorhombic structure, and this structure becomes more symmetric as the amount of Nd doping increases. The conductivity of BaCe_0.8Y_0.2−xNd_xO_3−δ depends on the amount of Nd doping and the operation temperature. AC impedance results indicate that the resistance of BaCe_0.8Y_0.2−xNd_xO_3−δ decreases as the temperature increases, with the majority of resistance coming from oxygen ion diffusion. The XRD peak intensity of BaCe_0.8Y_0.2O_3−δ apparently decreased with time, forming Ba(OH)₂ and CeO₂ second phases. The phase stability of BaCe_0.8Y_0.2−xNd_xO_3−δ (x = 0.05-0.2) samples is much better than that of BaCe_0.8Y_0.2O_3−δ, and it exhibited no second phase after tested in an 80 °C water bath for 18 h.     

pH-sensitive and bioadhesive poly(β-amino ester)-poly(ethylene glycol)-poly(β-amino ester) triblock copolymer hydrogels with potential for drug delivery in oral mucosal surfaces

A series of novel pH-sensitive triblock copolymers composed of poly(β-amino ester)-poly(ethylene glycol)-poly(β-amino ester) (PAE-PEG-PAE) were synthesized by conjugating poly(β-amino ester) to poly(ethylene glycol). The resulting polymers were characterized by ¹H and ¹³C NMR in CDCl₃ and gel permeation chromatography in tetrahydrofuran. The concentrated polymer solutions (30 wt%) exhibited a gel-to-sol transition in the pH range 6.4-7.8. The gel window spanned physiological conditions (37 °C, pH 7.4). After injection into a rat, the copolymer solution (30 wt%) changed to a gel in a short time. This copolymer hydrogel showed bioadhesive properties and in vitro release of lidocaine was controllable.     

Low-temperature sintering and microwave dielectric properties of CaSnxSiO(3+2x)-based positive τf compensator

The sinterability, phase compositions, and microwave dielectric properties of LiF-doped nonstoichiometric CaSn_xSiO_(3+2x) ceramics prepared by the solid-state reaction were investigated. LiF addition effectively reduced the sintering temperature of CaSn_xSiO_(3+2x) ceramics and inhibited the volatilization of Sn. A pure monoclinic CaSnSiO₅ phase was achieved in the 1.0?wt% LiF-doped CaSn_0.94SiO_4.88 ceramics sintered at 1175?°C, which exhibited good microwave dielectric properties of ε_r =?11.6, Q?×?f?=?34000?GHz, and τ_f =?+73.2?ppm/°C. The positive τ_f value was an atypical and important phenomenon for low-permittivity microwave dielectric ceramics, which could be a promising τ_f compensator.     

Synthesis of zinc oxide nanoparticles reinforced clay and their applications for removal of Pb (Ⅱ) ions from aqueous media

The aim of the study was to synthesize zinc oxide nanoparticles (ZnONPs) composite with clay by a novel route and then to explore the capability of composite of ZnONPs and silty clay (SC) as adsorbents for Pb (Ⅱ) eradication from aqueous media by batch adsorption method. The effect of different operating factors like temperature, pH, dose and time of contact on the adsorption process were studied to optimize the conditions. Langmuir, Freundlich, Dubinin–Radushkevich (D-R) and Temkin isotherms were applied for the interpretation of the process. The R2 and q values obtained from Langmuir model suggested that the process is best interpreted by this model. The values of adsorption capacity (qm) noted were 12.43 mg·g-1 and 14.54 mg·g-1 on SC and ZnONPs-SC respectively. The kinetic studies exposed that pseudo second order (PSO) kinetics is followed by the processes suggesting that more than one steps are involved to control the rate of reactions. Various thermodynamic variables such as change in free energy (ΔGΘ), change in enthalpy (ΔHΘ) and change in entropy (ΔSΘ) were calculated. Thermodynamic data suggested that Pb (Ⅱ) adsorption on SC and ZnONPs-SC are spontaneous, endothermic and feasible processes.     

Synthesis of (α- and β-)Si3N4/Si2N2O into silicon particulate porous preforms by hybrid system CVI and direct nitridation

An investigation on the microstructure and mechanical properties of Si/Si₃N₄/Si₂N₂O porous ceramic composites, synthesized in a multi-step approach via hybrid precursor system chemical vapor infiltration (HYSYCVI) and direct nitridation (DN) has been conducted. Particulate silicon porous preforms were infiltrated in subsequent stages S1-1, S1-2 (both at 1300 °C for 70 min in high purity nitrogen (HPN) using Na₂SiF₆ as solid precursor) and S2 (1350 °C for 120 min in ultra high purity nitrogen (UHPN)). Chemical reactions that account for the formation of Si₂N₂O and Si₃N₄ are proposed. Results show that the microstructure of the composites was influenced by atmosphere type and processing stage, affecting kind, morphology and size (including nanometric size) of nitrides formed. Porous composites (43% porosity) with modulus of rupture (MOR) ≈ 43 ± 3.5 MPa (evaluated in four-point bending tests) and elastic modulus (E) ≈ 29 GPa (determined by the pulse-echo ultrasonic method) are routinely obtained.