Orientation development in retensilized,biaxially oriented polypropylene films

A basic study of orientation development in retensilized, biaxially oriented polypropylene films was performed. Wide-angle X-ray scattering (WAXS) and birefringence measurement techniques were used to examine films prepared under specific processing conditions. Biaxial orientation factors were determined for these films and were correlated with end-use properties of the materials. In particular, the dispensability of oriented polypropylene films was found to correlate with crystalline-phase and amorphous-phase orientation factors. Dispensability is a relatively important property of pressure-sensitive tapes; it is defined as the force necessary to cut a film backing over a serrated blade of the type used in commercially available adhesive-tape dispensers.     

Thiol–ene networks and reactive surfaces via photoinduced polymerization of allyl ether functional hyperbranched polymers

A series of allyl ether functionalized hyperbranched (HB) polyester of three generations was synthesized from commercially available Boltorn^®. These modified HB polymers were homopolymerized to form films with a large number of residual allyl ether groups available for post film formation reactions. Additionally, the polyester multifunctional molecules were cured with a di and tetrathiol monomer in a one to one molar ratio to determine the effect of conversion on the resulting network thermal and physical properties. The same UV-cure chemistries were carried out with a similar second generation polyester dendrimer for comparison. This was in an effort to determine if there is any significant difference in the film chemical conversion and properties with dendrimers in comparison to HB molecules. The highly crosslinked films were obtained and characterized with respect to physical (DMTA) and thermal (DSC and TGA) properties.     

Preparation of high-modulus and high-strength poly(ethylene terephthalate) film by zone-annealing method

The zone-annealing method was attempted to prepare high-modulus and high-strength poly(ethylene terephthalate) (PET) film. The film having Young′s modulus of 14.5 × 10¹⁰ dyn/cm² and a tensile strength of 86.9 kg/mm² in the drawing direction was obtained. These values correspond to four times those of a biaxial-stretched PET film available commercially. The dyanmic viscoelastic properties also were measured. The dynamic storage modulus was 15.4 × 10¹⁰ dyn/cm² at room temperature, and a high value of 3.6 × 10¹⁰ dyn/cm² even at 200°C. The latter value is slightly higher than the room temperature modulus of the commercially available film. From the intensity and temperature position of α-dispersion E″ peak, it was suggested that the amorphous chains in the zone-annealed film was densely packed in a highly oriented state. Furthermore, the crystallinity, orientation, especially double orientation, and molecular chain conformation of the films in the zone-annealing process are discussed in the present paper.     

Interface Contributions to Localized Heating of Dielectric Thin Films

Measurements of the thermal conductivity of thin dielectric films in the last ten years have established that thin film thermal conductivity may be much lower than that of the corresponding bulk solid, by as much as two orders of magnitude, and that significant interfacial thermal resistance may be present along the film/substrate interface. We review such measurements of thin film thermal conductivity and interfacial thermal resistance, and use the heat conduction equation to determine their implications for the localized heating of thermally anisotropic thin films bonded to substrates. It is found that for surface heating an equivalent isotropic film can be established and that the presence of large interfacial thermal resistance leads to a strong dependence of film thermal conductivity on film thickness, especially for thin films. A microscopic model of the film/substrate interface is used to establish the dependence of the interfacial thermal resistance on porosity along the interface.     

The liquid-liquid interface as a medium to generate nanocrystalline films of inorganic materials

Unlike the air-water interface, the organic-aqueous (liquid-liquid) interface has not been exploited sufficiently for materials synthesis. In this Account, we demonstrate how ultrathin nanocrystalline films of metals such as gold and silver as well as of inorganic materials such as semiconducting metal chalcogenides (e.g., CdS, CuS, CdSe) and oxides are readily generated at the liquid-liquid interface. What is particularly noteworthy is that single-crystalline films of certain metal chalcogenides are also obtained by this method. The as-prepared gold films at the toluene-water interface comprise fairly monodisperse nanocrystals that are closely packed, the nature and properties of the films being influenced by various reaction parameters such as reaction temperature, time, reactant concentrations, mechanical vibrations, and the viscosity of the medium. The surface plasmon band of gold is markedly red-shifted in the films due to electronic coupling between the particles. The shift of the surface plasmon band of the Au film toward higher wavelengths with an accompanying increase in intensity as a function of reaction time marks the growth of the film. Depending on the reaction temperature, the Au films show interesting electrical transport properties. Films of metals such as gold are disintegrated by the addition of alkanethiols, the effectiveness depending on the alkane chain length, clearly evidenced by shifts of the surface plasmon bands. A time evolution study of the polycrystalline Au and CdS films as well as the single-crystalline CuS films is carried out by employing atomic force microscopy. X-ray reflectivity studies reveal the formation of a monolayer of capped clusters having 13 gold atoms each, arranged in a hexagonal manner at the toluene-water interface. The measurements also reveal an extremely small value of the interfacial tension. Besides describing features of such nanocrystalline films and their mode of formation, their rheological properties have been examined. Interfacial rheological studies show that the nanocrystalline film of Ag nanoparticles, the single-crystalline CuS film, and the multilayered CdS film exhibit a viscoelastic behavior strongly reminiscent of soft-glassy systems. Though both CuS and CdS films exhibit a finite yield stress under steady shear, the CdS films are found to rupture at high shear rates. An important advantage of the study of materials formed at the liquid-liquid interface is that it provides a means to investigate the interface itself. In addition, it enables one to obtain substrate-free single-crystalline films of materials.     

Influence of natural and accelerated weathering on performances of photoselective greenhouse films

The research aims to investigate the effects of natural and accelerated weathering on polyethylene‐based films. At this regard, monolayer films of low density/linear low density polyethylene blends, containing commercially available organic pigments and an UV absorber of the benzophenone type, have been considered. The samples were weathered on field (natural weathering) or using two different artificial procedures: UV lamp and QUV chamber. Conditioned film samples were, then, analyzed by performing several physical tests taking as‐received films as a reference. Rheological measurements showed an increase in viscosity of weathered sample melts as a consequence of photodegradation phenomena, inducing the formation of double bonds and crosslinks. This latter result was also confirmed by gel content measurements. UV–visible spectroscopic tests indicated that in both cases of natural and artificial weathering an increase of the transmittance of films occurred. Tensile tests indicated the increase of films stiffness, especially in case of samples conditioned using the UV lamp, and a large decrease of the strain at break, both in machine and in transverse directions, especially for film weathered using the QUV chamber. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Titanium Oxide Thin Films on Organic Interfaces through Biomimetic Processing

Titanium oxide (TiO₂) thin films have been deposited on silicon, glass, and plastic substrates by destabilization of an aqueous titanium lactate solution at low temperatures (<100°C). The process uses a commercially available, low-cost precursor and is simple to perform; it involves only control of pH in aqueous, chelated titanium solutions. With this solution technique, high deposition rates (>50 nm/min), film thickness (>100 nm), and excellent film uniformity have been obtained. Uniform coatings can be applied on complex-shaped polymeric substrates and porous membranes. Films can be formed on both sulfonated and untreated polymeric surfaces. As-deposited films on plastic substrates consist of amorphous, hydrated TiO₂. On sulfonated self-assembled monolayers on silicon substrates, nanocrystalline TiO₂ films have been formed. The deposited films exhibit strong ultraviolet (UV) absorption with excellent transmission in the visible wavelength range, which indicates that the coatings may be useful as protective UV blockers for polymeric materials.     

Evaluation of mechanical properties and hydrophobicity of room-temperature,moisture-curable polysilazane coatings

Polysilazane coatings have a broad need in real-life applications, which require low processing or working temperature. In this work, five commercially available polysilazanes have been spin-coated on polycarbonate substrates and cured in ambient environment and temperature to obtain transparent, crack-free, and dense films. The degree of crosslinking is found to have a significant impact on the hardness and Young's modulus of the polysilazane films but has a minor influence on the film thickness and hydrophobicity. Among all five polysilazane coatings, the inorganic perhydropolysilazane-based coating exhibits the largest hardness (2.05 ± 0.01 GPa) and Young's modulus (10.76 ± 0.03 GPa) after 7 days of curing, while the polyorganosilazane-derived films exhibit higher hydrophobicity. The molecular structure of polysilazanes plays a key role in mechanical properties and hydrophobicity of the associated films, as well as the adhesion of coatings to substrates, providing an intuitive and reliable way for selecting a suitable polysilazane coating material for a specific application.     

Thickness-direction thermal expansion of polyimide films

The coefficient of thermal expansion (CTE) for thin polymer films is a property of considerable practical importance. In contrast to the abundance of CTE data in the in-plane or film direction, data in the thickness or z-direction is rarely available, in part due to the high sensitivity required for measurement of the small thickness changes involved. In this paper, we will describe both a capacitance change and a Fabry-Perot laser interferometric method for measuring z-direction CTE's. Results are presented for a variety of commercially available polyimide films of thickness 50 to 130 μm. Upilex and Kapton were found to have z-direction CTE's of about 55 and 81 ppm/°C, respectively. These CTE's for the thickness direction are many times higher than the corresponding values in the in-plane direction. This anisotropy is attributed to the preferential in-plane molecular orientation of the polymer chains.     

Interfacial film properties of asphaltenes and resins

Interfacial film properties of asphaltenes and resins have been studied by interfacial shear viscosity measurements. The results show that the structure of the asphaltene film at the interface between oil and water is changed from two-dimensional to three-dimensional network as the concentration of the asphaltene at the interface increased. The film can be divided into three types namely expanded liquid film, condensed liquid film and solid-like three-dimensional network film. Furthermore, the structures of the interfacial films formed by asphaltene molecules and asphaltene particles are different and the strengths of these films are also different. The adsorption and migration processes of asphaltene molecules and migration process of asphaltene particles at the interface are different.     

Stretchable photochromic hydrous TiO2-embedded glycerol-poly(dimethylsiloxane) film for rewritable information storage

Photoreversible, color-changing films have great potential in various optical applications. In this study, we developed a photochromic film by embedding droplets of metatitanic acid (hydrous TiO₂) and glycerol in commercially available poly(dimethylsiloxane) (PDMS) silicone elastomers. Benefiting from the electron–hole pair scavenging abilities of glycerol, the resulting film exhibited rapid photoresponse, high photoreversible stability, excellent antiaging capability, and remarkable stretchability. The degree of color changes upon ultraviolet (UV) irradiation was effectively controlled by adjusting both the concentration of hydrous TiO₂ (1–20 wt%) and UV irradiation time (5–30 min), thereby increasing total color-changing ability (ΔE). High-resolution patterns could be repetitively printed, erased, and rewritten (≥20 times) with no significant loss of clarity. After a 30-day exposure to ambient air, there were no significant aging effects in the photochromic ability of the films, thus demonstrating promising potential as rewritable films for information storage.     

Compostability of cellulose acetate films

Composting is an accelerated biological decay process viewed by many to be a potential solution to the solid-waste management crisis existing in many parts of the world. As part of a program to develop environmentally nonpersistent polymers that are compatible with a composting environment, we have developed a bench-scale compost methodology that emulates a high efficiency municipal windrow composting operation. A series of cellulose acetate films, differing in degree of substitution, were evaluated in this bench-scale system. In addition, commercially available biodegradable polymers such as poly(hydroxybutyrate-co-valerate) (PHBV) and polycaprolactone (PCL) were included as points of reference. Based on film disintegration and on film weight loss, cellulose acetates, having degrees of substitution less than approximately 2.20, compost at rates comparable to that of PHBV. NMR and GPC analyses of composted films indicate that low molecular weight fractions are removed preferentially from the more highly substituted and slower degrading cellulose acetates. © 1994 John Wiley & Sons, Inc.     

Resistivity, Hall coefficient, magnetoresistance, and microtexture of cellulose carbon films

Dense carbon films of about 20 μm in thickness were prepared from a commercially available cellulose film of 40 μm thick by heat treatment up to 900°C. Carbon films thus obtained were heat treated at temperatures between 1800 and 3000°C for 30–60 min. The heat-treated carbon films were investigated by the measurements of resistivity, Hall coefficient and magnetoresistance at liquid nitrogen temperature. Reflected and transmitted X-ray diffraction experiments and observations by a high-resolution scanning electron microscope (SEM) were also carried out. The results of the resistivity and Hall coefficient for high-temperature-treated specimens indicated that the carbonized film was more graphitizable than bulk glass-like carbons. The magnetoresistance and X-ray diffraction profiles for the high-temperature-treated specimens suggested that each of these specimens substantially consisted of the matrix of granular microtexture and the graphite layer skin. The skin was clearly observed by SEM for the specimens heat-treated at 2800 and 3000°C and their thickness was 100–300 nm.     

熔体微分电纺PLA/ATBC纳米纤维膜吸油性能

静电纺丝制备的纳米纤维孔隙率高、吸附能力强,可用于高效地处理化工行业油污染问题。聚乳酸（PLA）作为生物可降解材料,来源广泛且不会造成二次污染,具有广阔的应用前景。本文利用自制的熔体微分电纺装置,制备了PLA/乙酰基柠檬酸三丁酯（ATBC）纤维膜,探究了物料性质和增塑剂ATBC含量对PLA纤维形貌及吸油性能的影响,并获得了最佳的纺丝温度和ATBC含量。研究表明,在纺丝温度为240℃、ATBC质量分数为10%时制备的纤维直径为320nm。该纤维膜水接触角为145°,表现出良好的疏水性能,吸油倍率为138.4g/g,是市售PP无纺布吸油性能的4～5倍,保油倍率为85.8g/g。重复吸/放油5次循环后,纤维膜仍具有良好的强度而未发生断裂且可继续进行吸油,重复使用性能较好,可被应用于化工行业油污染处理。     

Novel Self-Crosslinking Epoxy Oligomers for Cationic-Cure Coatings Applications

ABSTRACT

Novel epoxy functional oligomers containing phosphate-esters, carboxylate-ester, and urethane linkages with varying molecular weight and functionality have been synthesized from commercially available epoxy compounds. These oligomers are characterized for the parameters relevant to the study by physical, spectroscopic, and chemical methods. Two series of cationic thermal-cure coating compositions have been formulated using these oligomers as principal film-forming components. The cured films of these self-crosslinked oligomers have been studied and compared. A correlation between structure of these oligomers and their film properties has been established.     

Dye-sensitized solar cell based on optically transparent TiO2 nanocrystalline electrode prepared by atomized spray pyrolysis technique

Preparation of crack-free thin films of interconnected and non-agglomerated TiO₂ nanoparticles on electronically conducting fluorine doped tin oxide surfaces is instrumental in designing and developing transparent dye-sensitized solar cells (DSCs). A novel technique called “Atomized Spray Pyrolysis” (ASP) has been designed and developed to achieve such perfectly transparent thin films. Optical transmittance of TiO₂ films produced on FTO surface by this ASP method has been compared with those obtained by doctor-blading and by hand spray methods and found that the atomized spray pyrolysis technique give films with high transparency. Dye adsorption per gram of TiO₂ is 2.16 times higher in the sample produced by the ASP method when compared to the film produced by the hand spray method and is 1.60 times higher than that produced by the doctor-blading method using a commercially available TiO₂ nanocrystalline paste. SEM studies show the presence of interconnected discrete particles in the film produced by the ASP method. The fill factor (ff) remains almost constant for the cells with thickness from 6 μm to 13 μm but the highest photovoltage and photocurrent were found in ∼10 μm film based DSC which gave 8.2% conversion efficiency at AM 1.5 irradiation for cells of 0.25 cm² active area.     

Microstructure of Strontium Titanate Thin Film Grown by the Hydrothermal-Electrochemical Method

Microstructures of SrTiO₃ thin films grown on Ti substrates by the hydrothermal-electrochemical method have been studied by transmission electron microscopy. The grown films consisted of a thin surface layer having an isotropic polycrystalline structure and a thick inner layer having a columnar structure. Pores of the order of several tens of nanometers were found at boundaries of columnar grains constituting the inner layer. A 20- or 30-nm-thick polycrystalline layer of Ti oxides contaminated with a small amount of Sr was also found at the SrTiO₃ film/Ti substrate interface. During the film growth at this interface, the observed pores are considered to act as short-circuit paths for mass transport from the film surface to the interface.     

Quantifying Water at the Organic Film/Hydroxylated Substrate Interface

A method, based on Fourier transform infrared-multiple internal reflection (FTIR-MIR) spectroscopy, for determining the amount and thickness of water at an organic film/hydroxylated substrate interface has been developed. The analysis uses a two-layered model, which takes into account: 1) water at the organic film/hydroxylated substrate interface, 2) water taken up by the organic film within the penetration depth of the evanescent wave and 3) change of the penetration depth as water displaces the organic film from the substrate. Experimentally, the method requires the application of an organic film, transparent or opaque, of sufficient thickness on a hydroxylated internal reflection element, which is used as the substrate. A water chamber is attached to the organic-coated specimen. After adding water to the chamber, FTIR-MIR spectra are taken automatically at specified time intervals without disturbing the specimen or the instrument. Water uptake in the organic films and FTIR-MIR spectra of water on the substrates are also obtained and used for the analysis. Results of examples of three organic films: a clear epoxy, an unmodified asphalt, and a pigmented ester, on a hydroxylated SiO₂-Si substrate were presented to demonstrate the method. The water layer at the interface for the ester and asphalt specimens was found to be much thicker than that for the epoxy, and this was attributed to the presence of a water-sensitive layer accumulated at the interface for the formers. The method should be equally applicable to studies of organic and inorganic compounds at the organic film/hydroxylated substrate interface and their transport rates through films adhered to a substrate.     

Making powder aerosol deposition accessible for small amounts: A novel and modular approach to produce dense ceramic films

Powder aerosol deposition is a promising technique to deposit dense ceramic films directly at room temperature. While previous developments pointed towards larger and more complex deposition devices, this work follows a different approach and proposes a simplified and miniaturized coating device (denoted as Micro-PAD, µPAD). The aim is twofold: creating a smaller and flexible device consisting of an aerosol generation unit and a deposition chamber with a combined low areal footprint of 30 cm by 20 cm (that, e.g., easily fits in a glove box) as well as lowering the hurdle for other researchers to use the powder aerosol deposition. Therefore, we introduce a device mainly based on commercially available components/connectors as well as manual operated valves/flow meters. A key point is the elimination of moving components by just using a spot deposition that was enabled by using a circular de-Laval-type nozzle. The operational capability of µPAD is proven for the deposition of alumina films and compared to conventional PAD in terms of mechanical, crystalline, and optical film properties. Thick films with a bell-shape-like profile are deposited by µPAD, featuring a plateau in the center of the film with a diameter of 5 mm and a FWHM (full width at half maximum) diameter of about 10 mm. Alumina films produced by µPAD do not only match the properties of corresponding PAD films, but oftentimes outperform them. Here, µPAD films exhibit increased hardness and optical transmittance values, surpassing reference values of the conventional sprayed counterparts by at least 10%. Also, film integrity and adhesion to the substrate are slightly higher in case of µPAD. Reasons for the improved film properties are found by X-ray diffraction, with a significantly higher fracturing of impacting particles during µPAD combined with improved film consolidation as observed by SEM. Furthermore, µPAD featured doubled to tripled the deposition rates and, markedly almost doubled the deposition efficiency.     

Tuning the electronic properties of graphene by hydrogenation in a plasma enhanced chemical vapor deposition reactor

Graphene films grown by chemical vapor deposition on copper foils were hydrogenated using commercially viable methods. Parameters such as plasma power, plasma frequency, and sample temperature were varied to determine the maximum possible hydrogenation without etching the film. The kinetic energy of the ions inside the plasma is critical, in that higher kinetic energy ions tend to etch the film while lower kinetic energy ions participate in the hydrogenation process. The film sheet resistance was shown to increase, while the hole mobility was shown to decrease with increasing hydrogenation. Variable temperature measurements demonstrate a transition from semi-metallic behavior for graphene to semiconducting behavior for hydrogenated graphene. Sheet resistance measurements as a function of temperature also suggest the emergence of a bandgap in the hydrogenated graphene films.