Electrophoretic deposition of chiral polymers and composites

Electrophoretic deposition (EPD) method has been developed for the deposition of thin films of chiral polymers. EPD of poly-L-lysine (PLL) and poly-L-ornithine (PLO) films was performed for the first time on conductive substrates from aqueous and ethanol-water solutions. The deposition yield was monitored using a quartz crystal microbalance. The results demonstrated that the deposition yield can be varied by variation of the deposition time, voltage and polymer concentration in the solutions. It was shown that PLL and PLO provided stabilization and charging of hydroxyapatite (HA) nanoparticles in suspensions. Composite PLL-HA and PLO-HA films of controlled thickness were prepared by EPD. Electron microscopy investigations showed that the thickness of the PLL, PLO and composite films was varied in the range of 0-3 μm. The polymer and composite films can be used for biomedical applications.     

Electrophoretic deposition of TiO2 nanoparticles using organic dyes

Electrophoretic deposition method has been developed for the deposition of TiO(2) nanoparticles modified with organic dyes. Alizarin red, alizarin yellow and pyrocatechol violet dyes were used for the dispersion and charging of TiO(2) in ethanol and anodic electrophoretic deposition of TiO(2) films. The deposition yield was varied by the variation of dye concentration in suspensions and deposition time. Aurintricarboxylic acid dye was used for the deposition of TiO(2) from aqueous suspensions. It was found that thin films of pure aurintricarboxylic acid and composite aurintricarboxylic acid TiO(2) films can be obtained. The deposition yield was studied by quartz crystal microbalance. Dye film thickness was varied in the range of 0.1-2 μm by variation in the deposition time at a constant voltage. The composition of the films and the amount of the deposited material can be varied by the variation of TiO(2) and dye concentration in suspensions and deposition time. The films were studied by Fourier transform infrared spectroscopy, thermogravimetric analysis, differential thermal analysis and electron microscopy. The deposition mechanisms were discussed. The electrophoretic deposition method offers advantages for the fabrication of dye-sensitized TiO(2) films.     

A novel method for preparing and characterizing alcoholic EPD suspensions

Ceramic suspensions composed of alumina and mixtures of alumina and zirconia powders in ethyl alcohol were prepared. A solution of citric acid and triethylamine was used as dispersant. The citric acid, which usually is used as dispersant in water alumina suspensions, gave excellent results in ethyl alcohol also if it was used in conjunction with triethylamine. A novel method consisting of combined measurements of grain size, zeta potential, and transmittance was optimized to study the dispersion and stability properties of the ceramic suspensions; by using this method the optimal dispersant amount was determined. The suspensions based on alumina and alumina-zirconia powders were used to coat stainless steel plates by electrophoretic deposition (EPD); the optimal composition of suspensions and the used EPD parameters made it possible to obtain coatings with uniform thickness and composition.     

Additive-Free Electrophoretic Deposition of Graphene Quantum Dots Thin Films

The electrophoretic deposition (EPD) of graphene-based materials on transparent substrates is highly potential for many applications. Several factors can determine the yield of the EPD process, such as applied voltage, deposition time and particularly the presence of dispersion additives (stabilisers) in the suspension solution. This study presents an additive-free EPD of graphene quantum dot (GQD) thin films on an indium tin oxide (ITO) glass substrate and studies the deposition mechanism with the variation of the applied voltage (10–50 V) and deposition time (5–25 min). It is found that due to the small size (≈3.9 nm) and high content of deprotonated carboxylic groups, the GQDs form a stable dispersion (zeta-potential of about −35 mV) without using additives. The GQD thin films can be deposited onto ITO with optimal surface morphology at 30 V in 5 min (surface roughness of approximately (3.1±1.3) nm). In addition, as-fabricated GQD thin films also possess some interesting physico-optical properties, such as a double-peak photoluminescence at about λ=417 and 439 nm, with approximately 98 % visible transmittance. This low-cost and eco-friendly GQD thin film is a promising material for various applications, for example, transparent conductors, supercapacitors and heat conductive films in smart windows.     

阳极氧化TiN薄膜制备N掺杂纳米TiO2薄膜及其可见光活性

室温下通过电泳沉积(EPD)的方法在Ti片表面制备TiN薄膜, 然后对TiN薄膜进行阳极氧化得到N掺杂多孔纳米结构的TiO2薄膜. 利用X射线衍射(XRD), X射线光电子能谱(XPS), 扫描电子显微镜(SEM)及光电化学方法对得到的薄膜进行表征. XRD测试结果表明, 经过阳极氧化并在350 ℃空气气氛中退火1 h的薄膜中存在锐钛矿晶型的TiO2. XPS的结果表明, 样品中的N元素取代部分O, 且N的摩尔分数为0.95%. SEM显示, 经阳极氧化后薄膜表面出现多孔纳米结构. 光电化学测试结果显示, 阳极氧化提高了N掺杂TiO2薄膜在可见光下的光电响应. 经阳极氧化并热处理的薄膜在0 V电位及可见光照射下光电流密度为2.325 μA·cm-2, 而单纯热处理的薄膜在相同条件下光电流密度仅为0.475 μA·cm-2. 阳极氧化得到纳米多孔结构提高了N掺杂纳米TiO2薄膜的表面积, 从而对可见光的响应增大.     

Directed assembly of BaFe12O19 particles and the formation of magnetically oriented films

We have studied the preparation of oriented BaFe(12)O(19) films produced using electrophoretic deposition (EPD). Highly anisotropic, platelike BaFe(12)O(19) particles were synthesized under hydrothermal conditions, and from these particles, stable suspensions were prepared in 1-butanol by the addition of dodecylbenzene sulfonic acid as a surfactant. The interplay of the interaction forces between the suspended particles and the forces acting on the particles during the EPD directed the particles' assembly in the plane of the substrate. The most significant effect on the orientation of the films was the diameter-to-thickness ratio of the particles, which was experimentally confirmed with X-ray analyses, electron microscopy, and magnetic measurements. The abnormal grain growth that accompanied the sintering at 1150 °C further improved the overall orientation of the films, which showed highly anisotropic magnetic behavior with a remanent-to-saturation magnetization ratio exceeding 0.8.     

Electrophoretic deposition of polyacrylic acid and composite films containing nanotubes and oxide particles

Electrophoretic deposition (EPD) method has been developed for the deposition of thin films of polyacrylic acid (PAA). This method allowed the formation of uniform films of controlled thickness on conductive substrates. It was shown that PAA can be used as a common dispersing agent suitable for charging and EPD of various materials, such as multiwalled carbon nanotubes, halloysite nanotubes, MnO(2), NiO, TiO(2) and SiO(2). The feasibility of EPD of composite films containing the nanotubes and oxide particles in a PAA matrix has been demonstrated. The kinetics of deposition and deposition mechanisms were investigated and discussed. The films were studied by thermogravimetric analysis, differential thermal analysis, X-ray diffraction and scanning electron microscopy. The results indicated that film thickness and composition can be varied. Obtained results pave the way for the fabrication of PAA and composite films for biomedical, electrochemical and other applications.     

Films of lutetium bisphthalocyanine nanowires as electrochemical sensors

Lutetium bisphthalocyanine (LuPc(2)) nanowires have been successfully obtained by electrophoretic deposition (EPD). The influence of the deposition conditions and annealing in the structure of the films has been studied by AFM, SEM, X-ray diffraction (XRD), UV-vis absorption, and near-infrared (NIR). The electrochemical properties of the EDP films immersed in different electrolytic solutions (KCl, MgCl(2), KClO(4), HCl, and NaOH) indicate that anions diffuse inside the film to maintain the electroneutrality and the kinetics follows the Randles-Sevcik equation. The stability of the response increases strongly upon annealing due to the improvement of the adhesion of the sensitive material to the substrate. The EPD films have been successfully used to detect caffeic acid (an antioxidant of interest in the food industry). The anodic peak associated with the oxidation of caffeic acid appears at 0.54 V and is linearly dependent on the caffeic acid concentration in the 6 × 10(-5) M to 5 × 10(-4) M range with a detection limit of 3.12 × 10(-5) M. The electrochemical behavior of the annealed LuPc(2) EPD films is similar to that observed using Langmuir-Blodgett (LB) nanostructured films. However, the different molecular organization of the molecules inside the film causes differences in the shape and position of the peaks. Although LuPc(2) sensors prepared with both EPD and LB techniques provide stable and reproducible responses, the use of EPD is preferred for real sensing applications because of its lower cost, shorter preparation time, and longer lifetime.     

pH dependent stability of aqueous suspensions of graphene with adsorbed weakly ionisable cationic polyelectrolyte

Stable graphene suspensions were prepared through ultrasonic exfoliation followed by surface modification with the cationic polyelectrolyte poly(ethyleneimine) (PEI). The stability of the suspensions was found to be dependent upon the pH of the solution and the molecular weight of the PEI adsorbed. For the graphene sheets with adsorbed PEI with a molecular weigh of 600 Da, the particles were stabilised through an increased electrostatic repulsion at low pH inferred from in an increase in the measured zeta potential of the particles. However, the graphene with higher molecular weight PEI (70 kDa) was stable over a comparatively larger pH range through a combination of electrostatic repulsion at low pH and steric repulsion at elevated pH. Thus, solution conditions allowing the control of the colloidal sized graphene particles can be easily tuned through judicious management of solution conditions as well as polymer layer properties.     

Electrophoretic deposition of unstable colloidal suspensions for superhydrophobic surfaces

A novel method to fabricate superhydrophobic surfaces using electrophoretic deposition (EPD) is presented. EPD presents a readily scalable, customizable, and potentially low cost surface manufacturing process. Low surface energy materials with high surface roughness are achieved using EPD of unstable hydrophobic SiO(2) particle suspensions. The effect of suspension stability on surface roughness is quantitatively explored with optical absorbance measurements (to determine suspension stability) and atomic force microscopy (to measure surface roughness). Varying suspension pH modulates suspension stability. Contrary to most applications of EPD, we show that superhydrophobic surfaces favor mildly unstable suspensions since they result in high surface roughness. Particle agglomerates formed in unstable suspensions lead to highly irregular films after EPD. After only 1 min of EPD, we obtain surfaces with low contact angle hysteresis and static contact angles exceeding 160°. We also present a technique to enhance the mechanical durability of the superhydrophobic surfaces by adding a polymeric binder to the suspension prior to EPD.     

Electrophoretic deposition of Al2O3/ZrO2 layer with controllable thickness in ethanol medium

ZrO₂ toughened Al₂O₃ (Al₂O₃/ZrO₂) ceramic layers with required thickness were prepared by electrophoretic deposition (EPD) method using ethanol suspensions with stabilizing agent of polyethyleneimine (PEI) under constant-voltage mode in this paper. The deposition of Al₂O₃/ZrO₂ ceramic powders occurred on the titanium alloy cathode. A stable suspension with 1wt% PEI in ethanol at pH 5 was prepared in terms of the zeta potential and sedimentation of the suspension. The effects of the suspension concentration, applied voltage, deposition time and processing method of titanium alloy cathode on the coating thickness and morphology were investigated. The deposition layers on titanium alloys with smooth surfaces and thickness of 0.35?C1.2 mm could be obtained by adjusting the aforementioned parameters. In addition, after being sintered at 1500°C for 3 h in air atmosphere, ZrO₂ toughened Al₂O₃ ceramic layers became smooth and dense.     

Optimization of LiFePO4 nanoparticle suspensions with polyethyleneimine for aqueous processing

Addition of dispersants to aqueous based lithium-ion battery electrode formulations containing LiFePO(4) is critical to obtaining a stable suspension. The resulting colloidal suspensions enable dramatically improved coating deposition when processing electrodes. This research examines the colloidal chemistry modifications based on polyethyleneimine (PEI) addition and dispersion characterization required to produce high quality electrode formulations and coatings for LiFePO(4) active cathode material. The isoelectric point, a key parameter in characterizing colloidal dispersion stability, of LiFePO(4) and super P C45 were determined to be pH = 4.3 and 3.4, respectively. PEI, a cationic surfactant, was found to be an effective dispersant. It is demonstrated that 1.0 wt % and 0.5 wt % PEI were required to stabilize the LiFePO(4) and super P C45 suspension, respectively. LiFePO(4) cathode suspensions with 1.5 wt % PEI demonstrated the best dispersibility of all components, as evidenced by viscosity and agglomerate size of the suspensions and elemental distribution within dry cathodes. The addition of PEI significantly improved the LiFePO(4) performance.     

Electrophoretic deposition of titanate nanotube films with extremely large wetting contrast

A facile electrophoretic deposition (EPD) process has been developed to prepare thin films consisting of titanate nanotubes (TNTs) that were synthesized by a hydrothermal approach. Such an EPD process offers easy control in the film thickness and the adhesion to the substrate was found to be strong. The chemical composition and structure of the products have been characterized by XRD, HRTEM, and FESEM. It was found that the functionalization of TNTs plays a key role on the electrolyte stability and the formation of a uniform TNT film with good adhesion. The as-prepared TNT films show exceptional superhydrophilic behavior with ultra-fast spreading, while it converts to superhydrophobicity yet with strong adhesion after 1H,1H,2H,2H-perfluorooctyl-triethoxysilane modification. This study provides an interesting method to prepare films with extremely high wettability contrast that are useful for producing different types of functional materials.     

Controlled electrophoretic deposition of uniquely nanostructured star polymer films

The controlled electrophoretic deposition of polystyrene/divinylbenzene (PS/DVB) star polymer films from a colloidal suspension is reported. Liquid suspensions, containing the PS/DVB star polymer, were prepared by injecting a dichloromethane (DCM) solution of the star polymer into a stratified liquid combination of hexane and DCM. A variety of hexane/DCM volume ratios were examined to identify the optimal solution conditions for electrophoretic deposition; thin films were produced from both unmixed and well-mixed hexane/DCM suspensions. Unmixed suspensions yielded spatially separated thin films, deposited in a controlled fashion, that were dependent on the polarity of the corresponding electrode. Films on the positive electrode differed in thickness, microstructure, and appearance from those formed on the negative electrode. In contrast, films produced from well-mixed hexane/DCM suspensions deposited uniformly across only the negative electrode. Atomic force microscopy studies revealed nanostructured surface morphologies that were unique to each of these films. Additionally, these microscopy studies shed light on the possible conformations of star polymers adsorbed on a surface. By controlling the composition and the mixing state of the solution and by controlling the bias of electrodes, we achieved controlled deposition of star polymer films with a specific nanostructure. These nanostructured films may have broad use in optical and biological device applications.     

Composite films of polycations and TiO2 nanoparticles with photoinduced superhydrophilicity

We apply herein the reactive layer-by-layer (LBL) spray deposition of a polycation (polyethyleneimine, PEI) and a water soluble initiator of titanium dioxide [Ti(IV) bis(ammoniumlactato)dihydroxide, TiBisLac] to produce thin hybrid films containing PEI and nearly monodisperse TiO(2) anatase nanoparticles. The thickness of these coatings can be finely adjusted by either changing the number of deposition steps or the TiBisLac concentration. These films display intense absorption in the UV range and nearly full transparency above 365 nm and they also display photoinduced superhydrophilicity. These coatings can be produced either by reactive LBL spray deposition or reactive LBL dipping and may offer a wide range of applications from biology, as antibacterial coatings, to photoactive materials.     

液相沉积法制备光催化活性TiO2薄膜和纳米粉体

采用液相沉积法，在35℃通过向六氟钛酸铵水溶液中添加硼酸和结晶诱导剂锐 铁矿型TiO2纳米晶，沉积出具有光催化活性的Ti02薄膜和纳米粉体．用XRD，AFM， 阶梯仪,UV-vis，BET法对Ti02薄膜和粉体的沉积条件、结构、厚度和性能进行了测 定和表征，并用亚甲兰的降解，评价了TiO2薄膜和纳米粉体的光催化活性．结果表 明，当反应物六氟钛酸铵与硼酸的摩尔比为1：2—1：4时，沉积的粉体和薄膜含有 锐钛矿相Ti02；经300℃热处理的Ti02薄膜和纳米粉体具有最高的光催化活性，它 的光催化活性是未经热处理前的5倍．本文还解释了经300℃热处理的薄膜和纳米粉 体具有最高光催化活性的原因．     

Superhydrophobic surfaces formed using layer-by-layer self-assembly with aminated multiwall carbon nanotubes

A convenient and simple route to functionalized multiwall carbon nanotubes (MWNTs) using the reaction of the amine (NH) groups of polyethyleneimine (PEI) with MWNTs in N,N-dimethylformamide (DMF) at 50 degrees C is described. The product functionalized MWNTs (MWNT-NH-PEI) contain 6-8% by weight PEI based on elemental analysis, thermal gravimetric analysis, and titration. The products form stable emulsions in water below pH 9 and can be derivatized to form alkylated MWNTs that are dispersible in organic media. Such MWNT-NH-PEI nanoparticles can also be used in covalent or ionic layer-by-layer assembly to form nanocomposite thin films on functionalized polyethylene (PE) films and powders. Such nanocomposite films were analyzed by contact angle analysis, atomic force microscopy (AFM), and confocal Raman microscopy. These analyses show that these superhydrophilic surfaces have micro/nanoroughness with a roughly uniform distribution of MWNT nanoparticles. Superhydrophobic PE films can be formed either from ionic layer-by-layer self-assembly of MWNT-NH-PEIs and poly(acrylic acid) or from covalent layer-by-layer self-assembly of MWNT-NH-PEIs and Gantrez if the final graft is acrylated with a mixed anhydride prepared from ethyl chloroformate and octadecanoic acid. The resulting octadecylated surface produced by five covalent layer-by-layer deposition steps has a water contact angle of 165 degrees and a sliding angle of less than 5 degrees. The corresponding surface produced by five ionic layer-by-layer deposition steps has a water contact angle of 155 degrees but exhibits water pinning. The ionically assembled nanocomposite graft is labile under acidic conditions. The covalently assembled graft is more chemically robust.     

Formation of thin YSZ electrolyte films by electrophoretic deposition on porous cathodes

The structure, dispersity, stability, and electrophoretic deposition (EPD) of suspensions of spherical ZrO₂ stabilized Y₂O₃ (YSZ) nanoparticles with a mean size of 10.9 nm onto the porous surface of La_0.6Sr_0.4MnO₃ (LSM) with a pore size of 3–20 μm were studied by electron microscopy, photon correlation spectroscopy, and electroacoustical analysis. The optimum conditions of deposition were attained by using a mixed isopropanol-acetylacetone dispersion medium, which provided the aggregative stability of the suspension with 95% individual particles. The maximum pore size on the covered surface should be up to 0.5 μm if nanoparticles with a mean diameter of 10–20 nm are used. When the pores are larger, the EPD of YSZ will be effective if an additional intermediate LSM layer is formed by EPD to provide the required pore size.     

Hot filament chemical vapor deposition of poly(glycidyl methacrylate) thin films using tert-butyl peroxide as an initiator

We have demonstrated the successful deposition of poly(glycidyl methacrylate) (PGMA) thin films using hot filament chemical vapor deposition (HFCVD) with tert-butyl peroxide as the initiator. The introduction of the initiator allows for film deposition at low filament temperatures (<200 degrees C) and greatly improves the film deposition rates. The retention of the pendant epoxide chemical functionality and the linear polymeric structure in the deposited films were confirmed by infrared spectroscopy and X-ray photoelectron spectroscopy. The number-average molecular weight of the PGMA films can be systematically varied from 16,000 to 33,000 by adjusting the filament temperature and flow ratio of the initiator to the precursor. The apparent activation energies observed from PGMA deposition kinetics (100.9+/-9.6 kJ/mol) and from molecular weight measurements (-54.8+/-2.0 kJ/mol) are close to the calculated overall activation energies for the polymerization rate (104.4 kJ/mol) and number-average molecular weight (-59.2 kJ/mol), which supports the hypothesis of the free radical polymerization mechanism in the HFCVD PGMA deposition.     

In situ infrared molecular detection using palladium-containing zeolite films

In situ IR detection of carbon monoxide in the presence of hydrocarbons (methanol and pentane) using Pd-containing zeolite thin films is reported. The thin films are prepared by spin coating deposition of nanosized LTL and BEA type zeolites suspensions; the palladium clusters are introduced in the nanosized zeolites by ion exchange followed by γ radiolysis of the coating suspensions. The Pd-containing zeolite films with a thickness of 200 nm are exposed to a single gas (either CO or hydrocarbons) or gas mixtures in the presence of water (100 ppm), and the IR spectra are collected continuously at 25, 75, and 100 °C. The fast recognition of very low concentrations of CO (2-100 ppm) in the presence of highly concentrated vapors of methanol or pentane (400-4000 ppm) with the Pd-containing zeolite films is demonstrated. The detection of CO and hydrocarbons is instant, which is a function of the low thickness of the films, small size of the individual zeolite crystals, and regular size and high stability of the Pd clusters in the zeolite films. The heat of adsorption for all experiments is similar (15 kJ.mol(-1)), which is explained with weak interactions between the carbon monoxide and palladium clusters in the zeolite films at temperatures below 100 °C. The nanosized zeolites with homogeneously distributed Pd clusters deposited in thin films demonstrate high molecular recognition capacity toward low concentrations of carbon monoxide under real environmental conditions, i.e., in the presence of water and hydrocarbons.