Studies on structure property relationship in a polymer–clay nanocomposite film based on (PAN)8LiClO4

A new combination of ionically conducting polymer–clay nanocomposites based on (PAN)₈LiClO₄ + x wt % montmorillonite (unmodified) clay has been prepared using the standard solution cast process. X-Ray diffraction (XRD) analysis reveals strong interaction of polymer salt complex (PS) with the montmorillonite matrix evidenced by changes in d₀₀₁ spacing of the clay and enhancement in the clay gallery width on composite formation possibly due to intercalation of polymer–salt complex into nanometric clay galleries. Evidences of such an interaction among polymer–ion–clay components of the composite matrix has also been observed in the Fourier transform infrared (FTIR) spectrum results. FTIR results clearly indicated cation (Li⁺) coordination at nitrile (CN) site of the polymer backbone along with appearance of a shoulder suggesting strong evidence of polymer–ion interaction. Addition of clay into the PS matrix has been observed to affect ion–ion interaction resulting from ion dissociation effect at low clay loading in the PNC films. Complex impedance spectroscopy (CIS) analysis has provided a response comprising of a semicircular arc followed by a spike attributed respectively, to the bulk conduction and electrode polarization at the interfaces. Electrical transport appears to be predominantly ionic (t_ion = 0.99) with significant improvement in the electrical conductivity and thermal stability properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2577–2592, 2008     

A novel process for membrane fabrication: thermally assisted evaporative phase separation (TAEPS)

Poly(vinylidene fluoride) (PVDF) membranes fabricated from conventional processes have a limited range of microstructures. For example, PVDF membranes with spherulitic and isotropic microstructures containing macrovoids are extremely difficult to avoid using standard casting techniques such as wet-casting and thermally induced phase-separation (TIPS) casting. In order to create novel PVDF membrane microstructures such as a spongy, open-celled structure, a new membrane-formation process with six independent process parameters has been developed. Because this new process, thermally assisted evaporative phase separation (TAEPS), has a large number of parameters, the membrane microstructures are easily changed. The TAEPS process can fabricate a PVDF membrane with a spongy, anisotropic microstructure without macrovoids using a simple ternary system with no additives. In addition to studying the novel and unique microstructures available with the TAEPS process, the relationship between final morphology, performance, and processing conditions has been investigated in this paper.     

Preparation and characterization of TiO2/Pebax/(PSf‐PES) thin film nanocomposite membrane for humic acid removal from water

New thin film composite (TFC) membrane was prepared via coating of Pebax on PSf‐PES blend membrane as support, and its application in wastewater treatment was investigated. To modify this membrane, hydrophilic TiO₂ nanoparticles were coated on its surface at different loadings via dip coating technique. The as‐prepared membrane was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), field emission SEM, and contact angle analysis. The Fourier transform infrared spectroscopy analysis and surface SEM images indicated that TiO₂ was successfully coated on the membrane surface. In addition, the results stated that the hydrophilicity and roughness of membrane surface increased by addition of TiO₂ nanoparticles. Performance of TFC and modified TFC membranes was evaluated through humic acid removal from aqueous solution. Maximum permeate flux and humic acid rejection were obtained at 0.03 and 0.01 wt% TiO₂ loadings, respectively. Rejection was enhanced from 96.38% to 98.92% by the increase of feed concentration from 10 to 30 ppm. Additionally, membrane antifouling parameters at different pressures and feed concentration were determined. The results indicated that surface modification of membranes could be an effective method for improvement of membrane antifouling property.     

AFM,ellipsometry, XPS and TEM on ultra-thin oxide/polymer nanocomposite layers in organic thin film transistors

Here we report on the fabrication and characterization of ultra-thin nanocomposite layers used as gate dielectric in low-voltage and high-performance flexible organic thin film transistors (oTFTs). Reactive sputtered zirconia layers were deposited with low thermal exposure of the substrate and the resulting porous oxide films with high leakage currents were spin-coated with an additional layer of poly-α-methylstyrene (PαMS). After this treatment a strong improvement of the oTFT performance could be observed; leakage currents could be eliminated almost completely. In ellipsometric studies a higher refractive index of the ZrO₂/PαMS layers compared to the “as sputtered” zirconia films could be detected without a significant enhancement of the film thickness. Atomic force microscopy (AFM) measurements of the surface topography clearly showed a surface smoothing after the PαMS coating. Further studies with X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) also indicated that the polymer definitely did not form an extra layer. The polymer chains rather (self-)assemble in the nano-scaled interspaces of the porous oxide film giving an oxide–polymer “nanocomposite” with a high oxide filling grade resulting in high dielectric constants larger than 15. The dielectric strength of more than 1 MV cm⁻¹ is in good accordance with the polymer-filled interspaces.     

Polyaniline/poly(vinyl alcohol) (PAN/PVA) composite films: the synergy of film structural stiffening, redox amplification, and mobile species compositional dynamics

In this work, we report an unexpected but significant improvement of the redox behavior of conducting polyaniline (PAN) films by trapping intrinsically nonconducting poly(vinyl alcohol) (PVA) in the matrix of the polymer acting as stiffening and/or cross-linking agents. Film structural stiffening of PAN/PVA inclusion was studied in relation to film compositional dynamics. PAN and PAN/PVA composite films were potentiodynamically deposited using high-frequency electrochemical quartz crystal microbalance under electrochemical potentiodynamic control. From the simultaneously obtained measurements of nanogravimetric and cyclic voltammetric data, it has been found that the presence of PVA in the deposition solution increased the rate of PAN film growth as a function of PVA concentration. Characterization of the resultant composite films in monomer-free acidic electrolyte solutions showed significantly enhanced redox behavior of PAN/PVA composite films (with different PVA contents) compared to pure PAN by a factor of ～2–4. For the study of structure–composition relationships of composite polymer films, fluxes of instantaneous mobile species dynamics (ion/solvent) as a function of film redox conversion and potential cycling were correlated with film structural stiffening and the observed unusual redox enhancement of PAN/PVA composite films. Using various experimental timescales, we were able to resolve bound (associated with ion transfer) and free solvent compositional dynamics (associated with thermodynamic activity balance).     

Surface and interface analysis of electrochemically synthesized ferromagnetic/semiconducting Ni/GaAs(001) thin film

Thin film of ferromagnetic (FM) metal (Ni) on a semiconducting substrate (GaAs), i.e. Ni/GaAs(001), has been synthesized using electrochemical method. The structural, chemical and magnetic properties at the surface and interface have been investigated using X‐ray diffraction (XRD)/grazing incidence X‐ray reflectivity (GIXRR), X‐ray photoelectron spectroscopy (XPS) and magneto‐optical Kerr effect (MOKE) techniques, respectively. A crystalline peak observed at 44.4º in the XRD pattern, corresponding to Ni(111) Bragg peak, confirms the monocrystalline nature of the film. The atomic force microscopy image shows small‐sized spherical crystallites uniformly deposited over the substrate. The fitted GIXRR pattern confirms a smooth Ni/GaAs(001) film surface with roughness of less than ~5 ± 0.4 Å. The micro‐structural parameters, such as film thickness, surface and interface roughness, and electron density, are found to be ~230 ± 5 Å, ~4.5 ± 1 Å, ~0.5 ± 0.02 Å and ~6.38 ± 0.5 (Å^?2), respectively. The chemical nature of the film at the surface and interface, investigated using a depth profile XPS technique, shows no diffusion of metallic Ga and As into Ni layer or vice versa, confirming a sharp FM/semiconducting Ni/GaAs(001) interface. The magnetization behavior investigated using MOKE technique at room temperature shows a soft FM nature of the film with coercivity of ~75 Oe at the film surface. However, coercivity was found to be ~35 Oe at the interface. In addition, the saturation magnetization is also found to decrease at the interface with decreasing Ni layer thickness. The observed magnetization behavior is correlated with structural and chemical changes that occur at the interface of Ni/GaAs(001) film. Copyright © 2013 John Wiley & Sons, Ltd.     

Multicolor and fast electrochromism of nanoporous NiO/poly(3,4-ethylenedioxythiophene) composite thin film

We report a nanoporous NiO/poly(3,4-ethylenedioxythiophene) (PEDOT) composite film using a highly porous NiO film as a template by the combination of chemical bath deposition and electro-polymerization methods. The as-prepared NiO/PEDOT composite film has an interconnecting reticular morphology with nanometer sized pores ranging from 20–150 nm. The NiO/PEDOT composite film exhibits multicolor electrochromism with reversible color changes from purple to light blue brown and presents a transmittance variation of 31% at 600 nm. Fast switching speed is achieved in this composite film, and the response time for oxidation and reduction is 500 and 600 ms, respectively.     

Synthesis of block copolymers based on poly(2,3-epithiopropylmethacrylate) via RAFT polymerization and preliminary investigations on thin film formation

New block copolymers with narrow molecular weight distribution based on (2,3-epithiopropylmethacrylate) (ETMA), methylmethacrylate (MMA) and n-butylmethacrylate (nBMA) have been successfully synthesized via reversible addition-fragmentation transfer (RAFT) polymerization. First, RAFT homopolymerization of ETMA and MMA was carried out using 2-(2-cyanopropyl) dithiobenzoate (CPDB) as the chain transfer agent (CTA) and 2,2-azobisisobutyronitrile (AIBN) as the initiator. PETMA-b-P(nBMA) copolymers were synthesized using PETMA homopolymers as the macro-chain transfer agent (MCTA), while PMMA-b-PETMA diblock copolymers were synthesized using PMMA as the MCTA. The evolution of the molecular weight and molecular weight distribution of the homo- and co-polymers were compatible with the RAFT polymerization features. Thin films from the block copolymers were prepared by spin coating a 1 wt% polymer solution from toluene, chloroform or THF. After the preparation, the films were annealed under 80% vapor pressure of chloroform for 1, 2 and 4 h and investigated with scanning electron microscopy (SEM). The most interesting results were found in the films prepared using PETMA-b-P(nBMA) copolymers (). The observed images suggested the formation of hybrid lamellar structures, ascribed to the combination of its higher molecular weight and solvents viscosity.     

Poly(methyl methacrylate-co-methacrylic amide)-polyethylene glycol/polycarbonate and graphene nanoribbon-based nanocomposite membrane for gas separation

High-performance gas separation membranes were fabricated using 0.5–3wt.% graphene nanoribbon (GNR). Poly(methyl methacrylate-co-methacrylic amide)-polyethylene glycol (PMMA-co-MA-PEG) copolymer was prepared via condensation and blended with polycarbonate to form PMMA-co-MA-PEG/PC. The PMMA-co-MA-PEG/PC and GNR-based nanocomposite possess seamless micro-branched morphological pattern. Tensile strength and Young’s Modulus of PMMA-co-MA-PEG/PC/GNR0.5-3 increased from 64.3–74.7MPa and 76.7–99.9MPa, respectively. GNR loading increased the permselectivity αCO₂/N₂ (25.4–41.6) of nanocomposite membrane relative to blend membrane (20.1). However, permeability P_CO2 was decreased from 163.9 to 139.7 Barrer than blend (174.3 Barrer). PMMA-co-MA-PEG/PC/GNR revealed 51.6% increase and 24.7% decrease in permselectivity and permeability owing to molecular sieving and barricade characteristics of graphene nanoribbon.     

Phosphorus‐containing polyamide Mg(OH)2 nanocomposite coating on surface of poly(vinyl chloride) thin film: Study on thermal stability,flammability, and mechanical properties

Surface of poly(vinyl chloride) (PVC) thin films was coated using DOPO‐based polyamide (DBPA) coating and DBPA/Mg(OH)₂ nanocomposites (DBPN) coating by dip‐coating process. For this purpose, a new DOPO‐based dicarboxylic acid (DBDA) was synthesized and used for preparation of DBPA and organically surface modification of Mg(OH)₂ nanoparticles. The effects of DBPA and DBPN coatings on the morphology, thermal stability, combustion, and mechanical properties of PVC were investigated. The uniform dispersion of Mg(OH)₂ nanoparticles (nano‐MDH) and organically coating manner on the surface of the PVC films were confirmed by ATR‐IR spectroscopy, X‐ray diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), energy dispersive X‐ray, and elemental mapping. From thermal gravimetry analysis (TGA) results, the 10 mass% loss temperature (T₁₀) increased from 268°C to 272°C in PVC coated with DBPA‐containing 10 mass% of modified Mg(OH)₂ (MMH). Also the char residue, first and second mass loss temperatures of all PVC coated were increased compared with the neat PVC film. According to microscale combustion calorimetry (MCC) results, the peak of heat release rate (pHHR) and total heat release (THR) were decreased from 128 ± 2 to 69 W/g and 12 ± 1 to 4 ± 2 KJ/g for PVC film coated with DBPA‐containing 10 mass% of MMH, compared with the neat PVC. From tensile test results, tensile strength was increased from 31.78 ± 0.8 to 39.64 ± 0.9 MPa for PVC coated with polyamide‐containing 5 mass% of MMH compared with the neat PVC.     

Biodegradable graphene oxide nanosheets/poly-(butylene adipate-co-terephthalate) nanocomposite film with enhanced gas and water vapor barrier properties

Poly-(butylene adipate-co-terephthalate) (PBAT) has captured significant interest by dint of its biodegradability, superb ductility, promising processing properties and good final properties, but the insufficient barrier performance limits its application, especially in packaging field. In the present work, improved barrier properties of PBAT films were obtained by introducing an extremely low amount of graphene oxide nanosheets (GONS). O₂ and water vapor permeability coefficients were decreased by more than 70% and 36% at the GONS loading of 0.35 vol%, respectively. The enhanced barrier performance was ascribed to the outstanding impermeability and well dispersion of GONS as well as the strong interfacial adhesion between GONS and PBAT matrix. Furthermore, tensile strength and Young's modulus of GONS/PBAT nanocomposite rise up to 27.8 MPa and 72.2 MPa from 24.6 MPa to 58.5 MPa of neat PBAT, respectively, showing a prominent increase of mechanical properties compared to neat PBAT. The incorporation of GONS also endowed PBAT matrix with an excellent thermal stability. These findings provide a significant guidance for fabricating high barrier films on a large scale.     

Design and evaluation of polymer matrices for the encapsulation of CdSe/ZnS quantum dots in photonic nanocomposite thin films

A systematic approach and a new scheme for the evaluation of the as–is encapsulation of CdSe/ZnS core/shell quantum dots into polymer matrices is proposed, aiming to the implementation of thin film photonic integrated structures. Work focuses on quantum dots capped by hexadecylamine and trioctylphosphine oxide with no ligand exchange or other intermediate processing steps involved. The polymers studied include poly(methyl–methacrylate) (PMMA), polystyrene and acrylic polymers incorporating long alkyl chains, which are expected to promote the compatibility of the quantum dot ligands to that of the polymer chains. In this approach, the variation of photoluminescence properties of the nanocomposite thin films is measured versus increased concentration of the quantum dots, so as to evaluate the suitability of each polymer structure as an efficient host. Furthermore, the refractive index of the quantum dots/polymer nanocomposite thin films are also estimated using white light reflectance spectroscopy data, as appropriate for the integration of photonic devices. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 552–560     

Conductive-matrix-mediated alkaline Fe(III/VI) charge transfer: three-electron storage, reversible super-iron thin film cathodes

An extended conductive matrix facilitates a 100-fold enhancement in charge storage for reversible Fe(III/VI) super-iron thin films. These films were deposited, by electrochemical reduction of Na2FeO4, with an intrinsic high capacity 3 e- cathodic storage of 485 mAh g(-1). Whereas 3 nm Fe(III/VI) films exhibited a high degree of reversibility (throughout 100 charge/discharge cycles), thicker films had been increasingly passive toward the Fe(VI) charge transfer. Films were alternatively deposited on either smooth or on extended conductive matrixes composed of high-surface-area Pt, Ti, and Au and probed galvanostatically and via cyclic voltammetry. A 100 nm Fe(VI) cathode, on the extended conductive matrixes, sustained 100-200 reversible three-electrode charge/discharge cycles, and a 19 nm thin film cathode sustained 500 such cycles. With a metal hydride anode, full cell storage was probed, and a 250 nm super-iron film cathode film sustained 40 charge/discharge cycles, and a 25 nm film was reversible throughout 300 cycles. Fe(VI) salts exhibit higher cathodic capacity and environmental advantages, and the films are of relevance toward the next generation charge storage chemistry for reversible cathodes.     

Fabrication and luminescent properties of rare earths-doped Gd2(WO4)3 thin film phosphors by Pechini sol-gel process

Rare earth ions (Eu³⁺ and Dy³⁺)-doped Gd₂(WO₄)₃ phosphor films were prepared by a Pechini sol-gel process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM) and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting powders and films. The results of XRD indicate that the films begin to crystallize at 600°C and the crystallinity increases with the elevation of annealing temperatures. The film is uniform and crack-free, mainly consists of closely packed fine particles with an average grain size of 80 nm. Owing to an energy transfer from WO₄²⁻ groups, the rare earth ions show their characteristic emissions in crystalline Gd₂(WO₄)₃ phosphor films, i.e., (J=0, 1, 2, 3; J′=0, 1, 2, 3, 4, not in all cases) transitions for Eu³⁺ and (J=13/2, 15/2) transitions for Dy³⁺, with the hypersensitive transitions (Eu³⁺) and (Dy³⁺) being the most prominent groups, respectively. Both the lifetimes and PL intensity of the Eu³⁺ () and Dy³⁺ () increase with increasing the annealing temperature from 500°C to 800°C, and the optimum doping concentrations for Eu³⁺ and Dy³⁺ are determined to be 30 and 6 at% of Gd³⁺ in Gd₂(WO₄)₃ film host lattices, respectively.     

Ultrathin-film growth of para-sexiphenyl (II): formation of large-size domain and continuous thin film

The large-size domain and continuous para-sexiphenyl (p-6P) ultrathin film was fabricated successfully on silicon dioxide (SiO2) substrate and investigated by atomic force microscopy and selected area electron diffraction. At the optimal substrate temperature of 180 degrees C, the first-layer film exhibits the mode of layer growth, and the domain size approaches 100 microm(2). Its saturated island density (0.018 microm(-2)) is much smaller than that of the second-layer film (0.088 microm(-2)), which begins to show the Volmer-Weber growth mode. The characteristic of liquid-like crystal of p-6P monolayer film and the adequate diffusion of p-6P molecules dominate the formation of large-size domain. The coalescence of large-size domains offers the possibility to grow high-quality p-6P monolayer film which provides excellent substrate for weak epitaxy growth of phthalocyanine compounds.     

Sheathless capillary electrophoresis electrospray ionization‐mass spectrometry interface based on poly(dimethylsiloxane) membrane emitter and thin conducting liquid film

This study develops a sheathless CE‐MS interface using a robust PDMS membrane emitter and liquid‐film electric conduction. A 3D mold was constructed for casting the device by using a one‐step casting procedure. The interface consisted of a 125 μm‐thick triangular emitter with a 50 μm‐diameter microchannel, a conducting reservoir, and a 375 μm‐diameter channel for assembling the separation capillary. The separation capillary was inserted into the 375 μm channel and connected to the emitter through the conducting reservoir. The electric contact for the CE outlet was established through a conductive liquid film in the space between the capillary terminus and the 375 μm channel. The one‐step casting procedure and using a membrane emitter instead of a tapered emitter produced an easily fabricated and robust interface. A stable electrospray was obtained from 30 to 350 nL/min. Analyzing a five‐peptide mixture in low‐EOF (60 nL/min) and high‐EOF (210 nL/min) conditions demonstrated the utility of the interface.     

Facile fabrication of a novel high performance CO2 separation membrane: Immobilization of poly(amidoamine) dendrimers in poly(ethylene glycol) networks

Poly(amidoamine) (PAMAM) dendrimers showed high CO₂ separation properties and were successfully immobilized in a poly(ethylene glycol) (PEG) network upon photopolymerization of PEG dimethacrylate. The PAMAM dendrimer incorporation ratio was readily controlled, and a stable self-standing membrane containing up to 75 wt.% PAMAM dendrimer was obtained. The CO₂ separation properties over smaller H₂ were investigated by changing the PAMAM dendrimer content or generation and CO₂ partial pressure (ΔPCO₂$\mathrm{\Delta }{P}_{\text{C}{\text{O}}_2}$) under atmospheric conditions. Especially, a polymeric membrane containing 50 wt.% PAMAM dendrimer (0th generation) exhibited an excellent CO₂/H₂ selectivity of 500 with CO₂ permeability of 2.74 × 10⁻¹⁴ m³(STP)m/(m² s Pa) or 3.65 × 10³ barrer (1 barrer = 7.5 × 10⁻¹⁸ m³(STP)m/(m² s Pa)) when a mixture gas (CO₂/H₂: 5/95 by vol.) was fed at 25 °C and 100 kPa with 80% relative humidity. This polymeric materials are promising for a novel CO₂ separation membrane.     

CdTe@Cu(OH)2 nanocomposite: Aqueous synthesis and characterization

CdTe@Cu(OH)₂ nanocomposites were synthesized in aqueous solution by a seed-mediated growth approach. The effect of refluxing time and the concentration of Cu²⁺ on the preparation of these samples were measured using UV-visible absorption and photoluminescence analysis. The emission peak of the synthesized nanocomposites (CdTe@Cu(OH)₂) was shifted from 605 (CdTe seed) to 621 nm. The size of CdTe nanoparticles were averaged about 3.22 nm, and the CdTe@Cu(OH)₂ nanocomposites were averaged as 5.19 nm. The synthesized CdTe@Cu(OH)₂ nanocomposite were characterized with XRD, EDAX, TEM, FT-IR, EPR, and thermal analysis (TG/DTG curves). The results indicate that as-prepared nanoparticles with core/shell structure exhibit interesting optical properties.