A Novel Method for Preparing Nano‐ and Microcomposite Al2O3‐ZrO2 Ceramic Coatings

Nano‐ and microcomposite Al₂O₃‐ZrO₂ coatings were deposited on various substrates in a sol‐gel ceramic paint by a supercentrifugal force and a gradual sintering process. Fine metal oxide powders were dispersed in a sol‐gel solution by superpower ball milling so as to form a uniform stable ceramic paint. High‐resolution microscopy (FE‐SEM) was used to characterize the coating, indicating that the coating is composed of composite particle clusters with an average diameter of ～1 µm. The clusters consisted of larger particles with an average diameter of ～0.5 µm in center and smaller particles of ～100 nm surrounding the larger ones. The coating was relatively dense and increasingly dense toward the substrate surface.     

Triple redox/temperature responsive diselenide‐containing homopolypeptide micelles and supramolecular hydrogels thereof

Stimuli‐responsive polypeptides are receiving much attention for drug delivery systems and tissue engineering scaffolds; however, it is challenging to construct multiple‐responsive polypeptides and one‐component polymeric hydrogels. Herein, a novel type of triple redox/temperature‐responsive diselenide‐containing poly(methoxydiethylene glycol‐l ‐glutamate) homopolypeptide was facilely synthesized by selenocystamine‐initiated ring‐opening polymerization in DMF at 30 °C, and their chemical structures and physical properties were fully characterized by means of ¹H NMR, GPC, FT‐IR, WAXD, and CD. They self‐assembled into spherical micelles in aqueous solution, which possess a lower critical solution temperature, redox‐responsiveness inherited from diselenide bond, and the triple stimuli‐sensitive self‐assembly behaviors, as characterized by means of turbidity, DLS, TEM, and zeta potential measurements. The diselenide‐containing homopolypeptides formed supramolecular hydrogels at room temperature, exhibiting a thermal gel–sol transition. The rheological tests evidence that the mechanical modulus of the hydrogel is independent of angular frequency within 100 rad/s and at 25 °C, in which the storage modulus of G′ is order of magnitude greater than the loss modulus of G″, displaying a solid‐like elastic behavior. Moreover, the mechanical modulus of the hydrogel can be tuned by changing the chain length of the homopolypeptide, the 10‐mM 1,4‐dithiothreitol (DTT) reduction, and 1 mM H₂O₂ oxidation, respectively. Consequently, this work provides a simple strategy to fabricate triple‐stimuli responsive polypeptide micelles and one‐component hydrogels. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1067–1077     

Hydrothermal synthesis and characterization of nanocrystalline ZrO2 and surface modification with 2-acetoacetoxyethyl methacrylate

For the utilization as inorganic/organic hybrid nanomaterials for optical purposes, nanocrytalline tetragonal ZrO₂ was synthesized by hydrothermal method using zirconium(IV)-n-propoxide as precursor material. Surface of the ZrO₂ particles was then modified with 2-acetoacetoxyethyl methacrylate used as a copolymer for coatings. X-ray diffraction analysis revealed that both ZrO₂ and modified ZrO₂ are in tetragonal crystalline phase. As proved by transmission electron microscope and particle size analysis, average particle sizes of ZrO₂ and modified ZrO₂ were found as 6.22 and 14.7 nm, respectively. ZrO₂ powder was easily dispersed either in water or n-hexane. Ultraviolet diffuse reflectance spectrophotometer analysis for ZrO₂ and surface modified ZrO₂ showed that maximum absorption peaks are at 215 and 225 nm, respectively.     

Band gap tuning in nanocomposite ZrO2–SnO2 thin film achieved through sol–gel co-deposition method

Transparent SnO₂, nanocomposite ZrO₂–SnO₂ and ZrO₂ thin films were prepared by sol–gel dip-coating technique. X-ray diffraction (XRD) spectra showed a mixture of three phases: tetragonal ZrO₂ and SnO₂ and orthorhombic ZrSnO₄. X-ray photoelectron spectroscopy (XPS) gave Zr 3d, Sn 3d and O 1s spectra of the nanocomposite ZrO₂–SnO₂ thin film which revealed the presence of oxygen vacancies in the nanocomposite ZrO₂–SnO₂ thin film. Scanning electron microscopy (SEM) observations showed that microstructure of the nanocomposite ZrO₂–SnO₂ thin film consists of uniform dispersion of isolated SnO₂ particles in ZrO₂ matrix. The band gap for the ZrO₂ was estimated to be 5.51 eV and that for the nanocomposite ZrO₂–SnO₂ film was 4.9 eV. These films demonstrated the tailoring of band gap values which can be directly employed in tuning the band gap by simply changing the relative concentration of zirconium and tin elements. Photoluminescence (PL) spectra revealed an intense emission peak at 424 nm in the nanocomposite ZrO₂–SnO₂ film which indicate the presence of oxygen vacancies in ZrSnO₄.     

Enhanced sulfur‐resistant methanation performance over MoO3–ZrO2 catalyst prepared by solution combustion method

Sulfur‐resistant methanation of syngas was studied over MoO₃–ZrO₂ catalysts at 400°C. The MoO₃–ZrO₂ solid‐solution catalysts were prepared using the solution combustion method by varying MoO₃ content and temperature. The 15MoO₃–ZrO₂ catalyst achieved the highest methanation performance with CO conversion up to 80% at 400°C. The structure of ZrO₂ and dispersed MoO₃ species was characterized using X‐ray diffraction and transmission electron microscopy. The energy‐dispersive spectrum of the 15MoO₃–ZrO₂ catalyst showed that the solution combustion method gave well‐dispersed MoO₃ particles on the surface of ZrO₂. The structure of the catalysts depends on the Mo surface density. It was observed that in the 15MoO₃–ZrO₂ catalyst the Mo surface density of 4.2 Mo atoms nm^?2 approaches the theoretical monolayer capacity of 5 Mo atoms nm^?2. The addition of a small amount of MoO₃ to ZrO₂ led to higher tetragonal content of ZrO₂ along with a reduction of particle size. This leads to an efficient catalyst for the low‐temperature CO methanation process.     

Sol-Emulsion-Gel Synthesis of Alumina-Zirconia Composite Microspheres

Oxide microspheres in the system Al₂O₃-ZrO₂ (AZ), with the Al₂O₃:ZrO₂ molar ratios as 87:13, 78:22, 74:26 and 64:36 were obtained from emulsified bi-component sols by the sol-emulsion-gel method. The surfactant concentration and viscosity of the sols were found to affect the characteristics of the derived microspheres. The gel and calcined microspheres were investigated by using thermogravimetry analysis (TGA), differential thermal analysis (DTA), X-ray diffraction (XRD), optical and scanning electron microscopy (SEM) and particle size analysis. TGA indicated the removal of most of the volatiles, i.e. 40 ± 2 wt% up to about 500°C. Crystallization of gel microspheres at about 900°C was confirmed by DTA and XRD. XRD results also indicated the retainment of tetragonal (t-)ZrO₂, in the absence of stabilizers, at 1600°C. The optical and scanning electron microscopy confirmed the spherical morphology of the gel and calcined particles. The particle size distribution of the AZ microspheres calcined at 1200°C for 1 h exhibited a size range of 5–60 m with the average particle size (d ₅₀) varied from 23 to 26 m.     

Microgels based on isotactic poly(styrene): Synthesis and characterization

Poly(styrene) microgels are known, but the influence of tacticity on particle formation and behavior has not been investigated yet. Isotactic poly(styrene) (iPS) with M_n = 15–120 kg/mol is synthesized by coordinate polymerization and cross‐linked by Friedel–Crafts alkylation in a miniemulsion. Nuclear magnetic resonance (NMR) spectroscopy, light microscopy, cryogenic transmission electron microscopy, and wide‐angle powder diffraction are applied to understand the structure of microgels obtained. Typically, spherical microgels with overall diameter of 40–500 nm are found. Isotacticity of the polymer is retained during microgel formation. Increase of cross‐linker content leads to partial crystallinity inside the microgel. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 175–180     

Fast and excellent healing of hydroxypropyl guar gum/poly(N,N‐dimethyl acrylamide) hydrogels

In this article, a fast and high efficient healing hydroxypropyl guar gum (HPG)/poly(N,N‐dimethyl acrylamide) (PDMA) hydrogel is prepared by a facile synthesis method. HPG networks are formed through hydrogen‐bond interaction between the hydroxyl groups in the HPG chains, and PDMA networks are self‐crosslinked without any chemical crosslinker. The cut hydrogel could heal when nanosilica solution is chosen as the connector that is related to the adsorption of polymer to the surface of nanosilica. The fracture stress of the HPG/PDMA gels presents a fast and almost full recovery within a short time (1 min), while the recovery of fracture strain and elastic modulus is related to time in 2 h. The healing efficiency of HPG/PDMA gel is investigated as a function of healing time, HPG content, and N,N‐dimethyl acrylamide content. The microscopic healing process and healing mechanism are also discussed. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 239–247     

Thermomechanical investigation of a thick film of aniline-formaldehyde copolymer and poly(methyl methacrylate)

A thick film of aniline-formaldehyde copolymer and PMMA is synthesized via dispersion of aniline-formaldehyde copolymer powder as filler particles in PMMA with two different concentrations. Variation of the complex elastic modulus and mechanical loss factor (tanδ) with temperature is studied. It is observed that the complex elastic modulus decreases with temperature owing to thermal expansion of films. On the other hand, tanδ increases up to a characteristic temperature beyond which it shows a decreasing trend toward melting. Transition temperature T _g of sample S₁ (pure PMMA) is found to be 80°C. In sample S₂ (1 wt % aniline formaldehyde copolymer), the peak of tanδ at a lower temperature (66°C) corresponds to glass transition temperature T _g of the PMMA matrix, while the peak of tanδ at a higher temperature (107.8°C) corresponds to T _g of a polymer chain restricted by filler particles of aniline-formaldehyde copolymer. A further increase (10 wt % aniline-formaldehyde copolymer) in the concentration of filler particles of aniline-formaldehyde copolymer results in a more compact structure and a shift of T _g to a higher temperature, 122.2°C. This shift in the glass transition temperature of thick films of aniline-formaldehyde copolymer and PMMA is dependent upon the concentration of filler particles in the sample.     

Stress-induced compaction of concentrated dispersions of gel particles

 When submitted to successive shear stress steps, the elastic shear modulus of a concentrated dispersion of soft gel particles shows an exponential increase from 50 to 110 Pa. A slow relaxation time (τ _r ≃500 s) attributed to the mobility of the gel particles within their free volume is obtained. The amplitude of the relaxation time distribution decreases with the number of shear stress sequences, indicating a progressive decrease in the free volume available per particle. The results are explained by an increase in the packing density as grains rearrange under the external constraint. A rate constant is determined from the evolution of the dispersion's elastic modulus (K≃4 × 10⁻⁴ s⁻¹). The rate of compaction shows a logarithmic decrease when the initial particle's packing fraction is increased. Received: 5 October 1999 In revised form: 21 December 1999 Accepted: 21 January 2000     

Water effect on the rheologic behavior of PAN solution during thermal‐induced gelation process

The thermal‐induced gelation process in a polyacrylonitrile (PAN) solution containing different amounts of water was investigated through both dynamic and steady‐state rheologic measurements. During the cooling process, the storage modulus G′ was found to intersect with the loss modulus G″ at a temperature which can be considered as the incipient gel point T_ig. This crossover point increased with the water content in the PAN solution. On the basis of the power law $G'\tilde{G}\tilde{\omega} {}^{n} $ and the relation ${\rm tan}\ \delta = G(\omega )/G^{'}(\omega ) = {\rm tan}(n\pi /2) = {\rm const}$ , the loss tangent tan δ was traced with decreased temperature at various oscillation frequencies, and a crossover point was observed at the temperature a little higher than the T_ig above for all PAN solutions. The water content might affect the value of the relaxation exponent n via two different mechanisms, that is, hydration decoupling of the pendant nitrile groups in PAN at low water content (2 wt% water) and molecule aggregation at high water content (4 and 6 wt%). Nevertheless, the slight difference in the n values reflects the unique structure of the critical gels irrespective of the water level. The apparent viscosity η_a of either the PAN solution or the PAN gel was found to rise with increased water content and both showed pronounced shear‐thinning behavior. Compared with temperature, the water effect on the apparent viscosity η_a is more significant due to the water‐induced aggregation of the molecular chains. Copyright © 2010 John Wiley & Sons, Ltd.     

Milling assisted synthesis of calcium zirconate СаZrО3

Monophase calcium zirconate (CaZrO₃) has been prepared from the equimolar ZrO₂ + CaCO₃ mixture by two-step synthesis process. In the first step, mechanical treatment of the mixture is performed in an AGO-2 planetary ball mill. In the second step, the milled mixture is annealed to form calcium zirconate. High-energy ball milling of the (ZrO₂+CaCO₃) mixture results in decrease in the temperature of CaZrO₃ formation during annealing at 950 °C. The enhancement of CaZrO₃ synthesis is due to accumulation of excess energy by the reagents, decreasing the particle size and notable increase in the interphase area because of “smearing” of CaCO₃ on ZrO₂ particles during milling. Nanocrystalline calcium zirconate has been produced by controlling the annealing temperature and time.     

Preparation of ZrO2/silicone hybrid materials for LED encapsulation via in situ sol‐gel reaction

Organic silicones have been used as encapsulant materials for light‐emitting diodes (LEDs) for many years, while their performances need to be improved in order to satisfy the requirements of high‐power LEDs. A ZrO₂/silicone hybrid resin (ZHR) was synthesized for LEDs encapsulation by in situ sol‐gel reactions. The oligosiloxane was synthesized as polymeric matrix by nonaqueous sol‐gel condensation using diphenylsilanediol (DPSD), vinyltrimethoxysilane (VTMS), and 3‐methacryloxy propyl trimethoxysilane (MPTMS) as monomers. Then zirconium propoxide was added into this polymeric matrix to be hydrolyzed to obtain the hybrid resin with a uniform dispersion of ZrO₂ nanoparticles. The Si–O–Zr covalent bond was detected and benefited for excellent dispersibility of the ZrO₂ nanoparticles and the well compatibility between organic and inorganic phases. The cured ZHR with 5 wt% ZrO₂ content showed high light transmittance (greater than 80% in visible light range), high refractive index (=1.56), and high thermal stability (no yellowing at 150°C for 240 hours). The luminous flux of the LED chip with ZHR encapsulant was 10% higher than that of the pure silicone resin, suggesting that ZHR has great application potential in the field of LED packaging.     

Preparation and characterization of calcium hydroxyapatite and balloon-like calcium phosphate particles from forced hydrolysis of Ca(OH)2–triphosphate solution

Calcium phosphate particles were prepared by aging a solution of dissolved Ca(OH)₂ and sodium triphosphate (sodium tripolyphosphate, Natpp: Na₅P₃O₁₀) at 100–150 °C for 18 h in a Teflon-lined screw-capped Pyrex test tube. Large spherical and/or small aggregated spherical particles were precipitated with an extremely fast rate of reaction under 100 °C. The large spherical particles were amorphous and the small aggregated ones were α-CaNa₂P₂O₇^.4H₂O. The former amorphous ones crystallized to β-Ca₂P₂O₇ after being calcined above 600 °C. Calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, Hap), with rod-like and ellipsoidal or spherical aggregated shapes, was successfully produced using polyphosphates as a source of orthophosphate ions. Time resolved TEM measurement revealed that the crystallization of Hap particles takes place on the surface of tiny amorphous particles precipitated before aging. The tiny particles played the role of nuclei for Hap crystallization. The aging temperature drastically varied the particle shape under conditions for producing uniform amorphous spherical particles; solid spherical particles were produced with an aging temperature of up to 120 °C, whilst transparent balloon-like hollow spheres were precipitated at 125 °C. Finally, fully transparent balloon-like hollow spheres were produced with mere trace amounts of small rod-like particles after aging the solution above 127 °C. The time resolved TEM observation and ICP-AES measurements revealed that the balloon-like hollow spheres were produced by dissolving the interior of solid spherical particles after reinforcing their shell by the adsorption of unhydrolyzed tpp and/or pyrophosphate (pp) ions, which are the hydrolysis product of tpp. The balloon-like hollow spheres of calcium phosphate may have the potential use as drug delivery vehicles and have biocompatibility advantages.     

Synthesis and characterization of poly (1‐vinyl‐3‐butylimidazolium‐co‐methyl methacrylate) gel polymer electrolytes for dye‐sensitized solar cells: Effect of structure and composition

Herein, three ionic liquid random copolymers (P) containing 1‐vinyl‐3‐butylimidazolium bromide (VBImBr) and methyl methacrylate (MMA) with various molar ratios were prepared using conventional free radical polymerization. Afterward, their corresponding chemically cross‐linked copolymers (XP) were formed similarly in the presence of polyethylene glycol dimethacrylate (PEGDMA). The synthesized copolymers were characterized using FT‐IR, ¹H NMR, and GPC. Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) results showed that the rigidity and thermal stability of the copolymers depended on the ionic liquid content as well as the degree of cross‐linking. Gel polymer electrolytes were then prepared via obtained copolymers in the presence of a constant amount of synthesized imidazolium‐based ionic liquid. Among the copolymers, the P3 with in feed VBImBr:MMA molar ratio of 70:30 and the cross‐linked 1%‐XP3 copolymer prepared with 1 mol% of PEGDMA exhibited the highest conductivity and diffusion coefficients for I₃^¯ and I^¯. The power conversion efficiency of the optimized linear and cross‐linked copolymers (P3 and 1%‐XP3) under the simulated AM 1.5 solar spectrum irradiation at 100 mW cm^?2 were 3.49 and 4.13% in the fabricated dye‐sensitized solar cells (DSSCs), respectively. The superior long‐term stability and high performance of the gel electrolyte containing 1%‐XP3 suggested it as commercial gel electrolyte for future DSSCs.     

Influence of the preparation conditions of Pd‐ZrO2 and AuPd‐ZrO2 nanoparticle–decorated functionalised MWCNTs: Electron spectroscopy study aided with the QUASES

The Pd, AuPd, and ZrO₂ nanoparticle–decorated functionalised multiwalled carbon nanotubes (f‐MWCNTs) were reported as efficient catalysts of formic acid (FA) electro‐oxidation. Different preparation conditions influence their chemical and structural properties analysed by X‐ray photoelectron spectroscopy aided with the quantitative analysis of surfaces by electron spectroscopy. Different reduction procedures such as NaBH₄, a polyol microwave‐assisted method (PMWA), and a high pressure microwave reactor (HPMWR) were applied for decorating ZrO₂/f‐MWCNTs with Pd and AuPd nanoparticles. The ZrO₂ nanoparticles are attached through oxygen groups to the surface of f‐MWCNTs. In NaBH₄ and HPMWR procedures, Pd nanoparticles precipitate predominantly on ZrO₂ of nearly nominal stoichiometry, whereas in PMWA procedure, Pd and AuPd nanoparticles precipitate predominantly on the surface of f‐MWCNTs, bridging with oxygen groups and ZrO_x (x < 2) and leading to Pd‐O‐Zr phase formation. Strong reducing procedures (NaBH₄ and FA) led to smaller Pd nanoparticle size, Pd oxide content, and PdO_x overlayer thickness in contrary to weak reduction procedures (HPMWR and PMWA). The highest content of Pd‐O‐Zr phase appeared for Pd predominant precipitation on ZrO₂ nanoparticles (HPMWR) in contrary to Pd and AuPd predominant precipitation on surface of f‐MWCNTs (NaBH₄ ~ FA > PMWA). Larger content of Pd‐O‐Zr phase in AuPd‐decorated ZrO₂/f‐MWCNTs in contrary to Pd‐decorated sample (PMWA) could be justified by different electronic properties of nanoparticles. The FA treatment of Pd and AuPd‐ZrO₂/f‐MWCNTs samples provided decreasing Pd oxide content, overlayer thickness, nanoparticle size, increasing nanoparticle surface coverage and density, amount of Pd‐O‐Zr, what results from reduction of oxygen groups bridging with Pd and ZrO_x nanoparticles, also through Pd‐O‐Zr phase.     

Enrichment specificity of micro and nano‐sized titanium and zirconium dioxides particles in phosphopeptide mapping

Owning to their anion‐exchange properties, titanium and zirconium dioxides are widely used in phosphopeptide enrichment and purification protocols. The physical and chemical characteristics of the particles can significantly influence the loading capacity, the capture efficiency and phosphopeptide specificity and thus the outcome of the analyses. Although there are a number of protocols and commercial kits available for phosphopeptide purification, little data are found in the literature on the choice of the enrichment media. Here, we studied the influence of particle size on the affinity capture of phosphopeptides by TiO₂ and ZrO₂. Bovine milk casein derived phosphopeptides were enriched by micro and nanoparticles using a single‐tube in‐solution protocol at different peptide‐to‐beads ratio ranging from 1 : 1 to 1 : 200. Unsupervised hierarchical cluster analysis based on the whole set of Matrix Assisted Laser Desorption/Ionization time‐of‐flight mass spectra of the phosphopeptide enriched samples revealed 62 clustered peptide peaks and shows that nanoparticles have considerably higher enrichment capacity than bulk microparticles. Moreover, ZrO₂ particles have higher enrichment capacity than TiO₂. The selectivity and specificity of the enrichment was studied by monitoring the ion abundances of monophosphorylated, multiphosphorylated and non‐phosphorylated casein‐derived peptide peaks at different peptide‐to‐beads ratios. Comparison of the resulting plots enabled the determination of the optimal peptide‐to‐beads ratios for the different beads studied and showed that nano‐TiO₂ have higher selectivity for phosphopeptides than nano‐ZrO₂ particles. Copyright © 2013 John Wiley & Sons, Ltd.     

Statistical Megamer Morphologies and Materials from PAMAM Dendrimers

Summary: Generation‐4 poly(amidoamine) dendrimers (G4‐PAMAM) were cross‐linked using gluteraldehyde to obtain aldehyde‐activated G4‐PAMAM and cross‐linked G4‐PAMAM, termed pre‐megamers, which were grafted with octadecylamine (ODA) in chloroform (CHCl₃). Statistical megamer morphologies and particles were prepared by an emulsification solvent‐evaporation method using an ODA‐premegamer/CHCl₃ solution, surfactant, and water. Physicochemical characterization of the premegamers and megamers by various spectroscopic and microscopic techniques demonstrated their formation and properties useful in diagnostic and chromatographic applications.

Formation of pre‐megamers and megamers and their transmission electron microscopy images.     

Synthesis of zirconia‐incorporated titania layer by microarc oxidation for biomedical applications

The structural features, biocompatibility, and mechanical performance of a titania (TiO₂) layer with incorporated zirconia (ZrO₂) formed by microarc oxidation on commercially pure titanium have been examined in the present study. In comparison to the ZrO₂‐free TiO₂ layer, the ZrO₂‐incorporated oxide layer was dense and contained ZrTiO₄ as a new oxide as well as ZrO₂ particles. Associated changes in the microstructure enhanced the mechanical durability of TiO₂ layer. Owing to the incorporation of identical biocompatible compounds and almost similar surface roughness, no remarkable difference in bioactivities of the ZrO₂‐free and ZrO₂‐incorporated oxide layers was detected after simulated body fluid tests. Copyright © 2015 John Wiley & Sons, Ltd.     

Self‐Assembly Fractal Microstructures of HPAM/Chromium Acetate and HPAM/Phenolic Aldehyde Colloidal Dispersion Gel

Abstract

HPAM (partially hydrolyzed polyacrylamide)/chromium acetate and HPAM/phenolic aldehyde colloidal dispersion gels (CDGs) were investigated microscopically using atomic force microscope. The results show that the colloidal dispersion gels eventually form self‐assembly branch‐like fractal structures over a scanning range of micrometers. The fractal aggregates of single twigs formed by compact assembly of nanometer particles were observed over a smaller scanning range regardless of the concentration of HPAM and the crosslinking reagent. This indicated an HPAM‐dependence for the formation of the fractal structure and the crosslinking reagent independence of the geometrical morphology of the gel. Also, the results demonstrated that the elastic modulus (G′) of the fractal structure formed by the smaller (nanometer‐sized) colloidal particles was one order of magnitude higher than obtained for the micrometer‐sized particles. The elastic modulus (G′) and the dynamic stability of the gels increased with decreasing particle diameter.