Piezoelectricity and pyroelectricity of polyvinylidene fluoride corona-poled at elevated temperature

X-ray diffraction, thermally stimulated depolarization, and piezoelectric and pyroelectric current measurements have been carried out on biaxially oriented polyvinylidene fluoride film, corona-poled both negatively and positively, at elevated temperature. Larger piezoelectric and pyroelectric coefficients are obtained at lower values of the poling field, when corona charging takes place at elevated temperature rather than room temperature. Negative charging is more effective than positive. The polarization mechanism is dipole alignment, and a conversion of Form-II crystallites to Form I. The large space-charge injected by the corona, and trapped in the material, acts through creation of high internal fields, and shows little, if any, piezoelectric and pyroelectric effects of its own.     

Microscale patterning of thermoplastic polymer surfaces by selective solvent swelling

A new method for the fabrication of microscale features in thermoplastic substrates is presented. Unlike traditional thermoplastic microfabrication techniques, in which bulk polymer is displaced from the substrate by machining or embossing, a unique process termed orogenic microfabrication has been developed in which selected regions of a thermoplastic surface are raised from the substrate by an irreversible solvent swelling mechanism. The orogenic technique allows thermoplastic surfaces to be patterned using a variety of masking methods, resulting in three-dimensional features that would be difficult to achieve through traditional microfabrication methods. Using cyclic olefin copolymer as a model thermoplastic material, several variations of this process are described to realize growth heights ranging from several nanometers to tens of micrometers, with patterning techniques include direct photoresist masking, patterned UV/ozone surface passivation, elastomeric stamping, and noncontact spotting. Orogenic microfabrication is also demonstrated by direct inkjet printing as a facile photolithography-free masking method for rapid desktop thermoplastic microfabrication.     

Optical coherence tomography image analysis of polymer surface layers in sound-absorbing fibrous composite materials

The material surface layer affecting sound absorption was identified by optical coherence tomography (OCT) image analysis. To characterise this layer, a special algorithm was developed to distinguish the polymer surface layer in thermoplastic composite materials, define its structure and thickness, and specify differences in these properties. The composite materials were obtained by thermal pressing of multilayer systems comprising viscose/polylactide and polylactide nonwoven fabrics, yielding thin polymer surface layers on the order of several hundred micrometres. The results of the measured sound absorption coefficient were analysed together with the OCT results. The use of OCT for the study of materials with specific acoustic characteristics was successfully demonstrated.     

Highly conductive nanostructured C-TiO2 electrodes with enhanced electrochemical stability and double layer charge storage capacitance

The present work reports the structural and electrochemical properties of carbon-modified nanostructured TiO(2) electrodes (C-TiO(2)) prepared by anodizing titanium in a fluoride-based electrolyte followed by thermal annealing in an atmosphere of methane and hydrogen in the presence of Fe precursors. The C-TiO(2) nanostructured electrodes are highly conductive and contain more than 1 × 10(10) /cm(2) of nanowires or nanotubes to enhance their double layer charge capacitance and electrochemical stability. Electrogenerated chemiluminescence (ECL) study shows that a C-TiO(2) electrode can replace noble metal electrodes for ultrasensitive ECL detection. Dynamic potential control experiments of redox reactions show that the C-TiO(2) electrode has a broad potential window for a redox reaction. Double layer charging capacitance of the C-TiO(2) electrode is found to be 3 orders of magnitude higher than an ideal planar electrode because of its high surface area and efficient charge collection capability from the nanowire structured surface. The effect of anodization voltage, surface treatment with Fe precursors for carbon modification, the barrier layer between the Ti substrate, and anodized layer on the double layer charging capacitance is studied. Ferrocene carboxylic acid binds covalently to the anodized Ti surface forming a self-assembled monolayer, serving as an ideal precursor layer to yield C-TiO(2) electrodes with better double layer charging performance than the other precursors.     

Loss and recovery in hydrophobicity of silicone rubber exposed to corona discharge

This paper describes the loss and recovery in the hydrophobicity of unfilled high temperature vulcanized silicone rubber (HTV-SR) resulting from corona discharge. In this study, HTV-SR specimens were exposed to corona stress generated by a parallel needle-plane electrode system, and physicochemical analyses on the surface layer of SR before and after corona discharge treatment were carried out by using Fourier transform infra-red (FTIR) spectroscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It is demonstrated that hydrophilic OH groups that are by-products of ageing can be formed instead of hydrophobic CH₃ groups on the surface of aged SR and the corona discharge plays an important role on the temporary loss of hydrophobicity. After a substantial period of ‘rest’, the hydrophobic recovery of SR results from the diffusion of low-molecular weight (LMW) silicone fluid from the bulk onto the aged layer.     

Ionic liquid ion sources: suppression of electrochemical reactions using voltage alternation

The problem of electrochemical decomposition due to extraction of single polarity ions from a novel ionic liquid ion source (ILIS) is solved by periodically alternating the voltage source so that the potential difference that appears across the double layer formed between the emitter conductive material and the liquid is maintained below the electrochemical window limit, thus eliminating electronic reactions. The ionic liquid EMI-BF(4) is used to externally wet a solid tungsten emitter, establishing a physical boundary with a certain liquid-metal contact area. Theoretical and experimental evidence suggests that this area is close to the effective surface involved in the double layer charging dynamics. The extent of this surface is relatively large, thus increasing the net capacitance and consequently the double layer charging time, demonstrating that low frequency voltage alternation of the order of 1 Hz is enough to obtain clean and reliable ion emission.     

Photoinduced relaxation of surface charge in a dye-polyvinylcarbazole layer

Single-layer and dual-layer xerographic photoreceptors based on polyvinylcarbazole, a novolac resin, and the pyrocatechol violet dye were studied. The single-layer photoreceptors exhibited an order of magnitude higher photosensitivity as compared with their dual-layer counterparts. It was found that the character of conductivity decay in a photoreceptor after positive or negative corona charging of its outer surface depended on the technological conditions of substrate pretreatment.     

Electrochemical control of adsorption dynamics of surface layer proteins on gold

The kinetics and mechanism of the adsorption of the surface layer proteins of Lysinibacillus sphaericus CCM2177 on gold depend on the charging conditions of the electrochemical double layer and the addition of Ca(2+) ions. The electrical and mass charging was monitored by an in situ electrochemical quartz microbalance. Adsorption and monolayer formation of the protein molecules occur in the positive potential region where solvated anions form the electrochemical double layer. The crystalline character of the surface layer was diagnosed by an atomic force microscope. Negative of the point of zero charge, multilayer island structures were found.     

Charge assisted laser desorption/ionization mass spectrometry of droplets

We propose and evaluate a new mechanism to account for analyte ion signal enhancement in ultraviolet-laser desorption mass spectrometry of droplets in the presence of corona ions. Our new insights are based on timing control of corona ion production, laser desorption, and peptide ion extraction achieved by a novel pulsed corona apparatus. We demonstrate that droplet charging rather than gas-phase ion-neutral reactions is the major contributor to analyte ion generation from an electrically isolated droplet. Implications of the new mechanism, termed charge assisted laser desorption/ionization (CALDI), are discussed and contrasted with those of the laser desorption atmospheric pressure chemical ionization method (LD-APCI). It is also demonstrated that analyte ion generation in CALDI occurs with external electric fields about one order of magnitude lower than those needed for atmospheric pressure matrix assisted laser desorption/ionization or electrospray ionization of droplets.     

Water oxidation at hematite photoelectrodes: the role of surface states

Hematite (α-Fe(2)O(3)) constitutes one of the most promising semiconductor materials for the conversion of sunlight into chemical fuels by water splitting. Its inherent drawbacks related to the long penetration depth of light and poor charge carrier conductivity are being progressively overcome by employing nanostructuring strategies and improved catalysts. However, the physical-chemical mechanisms responsible for the photoelectrochemical performance of this material (J(V) response) are still poorly understood. In the present study we prepared thin film hematite electrodes by atomic layer deposition to study the photoelectrochemical properties of this material under water-splitting conditions. We employed impedance spectroscopy to determine the main steps involved in photocurrent production at different conditions of voltage, light intensity, and electrolyte pH. A general physical model is proposed, which includes the existence of a surface state at the semiconductor/liquid interface where holes accumulate. The strong correlation between the charging of this state with the charge transfer resistance and the photocurrent onset provides new evidence of the accumulation of holes in surface states at the semiconductor/electrolyte interface, which are responsible for water oxidation. The charging of this surface state under illumination is also related to the shift of the measured flat-band potential. These findings demonstrate the utility of impedance spectroscopy in investigations of hematite electrodes to provide key parameters of photoelectrodes with a relatively simple measurement.     

Carbohydrate‐Based Nanocarriers Exhibiting Specific Cell Targeting with Minimum Influence from the Protein Corona

Whenever nanoparticles encounter biological fluids like blood, proteins adsorb on their surface and form a so‐called protein corona. Although its importance is widely accepted, information on the influence of surface functionalization of nanocarriers on the protein corona is still sparse, especially concerning how the functionalization of PEGylated nanocarriers with targeting agents will affect protein corona formation and how the protein corona may in turn influence the targeting effect. Herein, hydroxyethyl starch nanocarriers (HES‐NCs) were prepared, PEGylated, and modified on the outer PEG layer with mannose to target dendritic cells (DCs). Their interaction with human plasma was then studied. Low overall protein adsorption with a distinct protein pattern and high specific affinity for DC binding were observed, thus indicating an efficient combination of “stealth” and targeting behavior.     

Surface charging behaviors of electrocatalytic interfaces with partially charged chemisorbates

The surface charge is a key concept in electrochemistry. Mathematically, the surface charge is obtained from a spatial integration of the volume charge along a particular direction. Ambiguities thus arise in choosing the starting and ending points of the integration. As for electrocatalytic interfaces, the presence of chemisorbates further complicates the situation. In this minireview, I adopt a definition of the surface charge within a continuum picture of the electric double layer. I will introduce surface charging behaviors of firstly ordinary electrochemical interfaces and then electrocatalytic interfaces featuring partially charged chemisorbates. Particularly, the origin of nonmonotonic surface charging behaviors of electrocatalytic interfaces is explained using a primitive model. Finally, a brief account of previous studies on the nonmonotonic surface charging behavior is presented, as a subline of the spectacular history of electric double layer.     

Aqueous electrochemistry of poly(vinylanthraquinone) for anode-active materials in high-density and rechargeable polymer/air batteries

A layer of poly(2-vinylanthraquinone) on current collectors underwent reversible electrode reaction at -0.82 V vs Ag/AgCl in an aqueous electrolyte. A repeatable charging/discharging cycles with a redox capacity comparable to the formula weight-based theoretical density at the negative potential suggested that all of the anthraquinone pendants in the layer was redox-active, that electroneutralization by an electrolyte cation was accomplished throughout the polymer layer, and that the layer stayed on the current collector without exfoliation or dissolution into the electrolyte during the electrolysis. The charging/discharging behavior of the polymer layer in the aqueous electrolyte revealed the capability of undergoing electrochemistry even in the nonsolvent of the pendant group, which offered insight into the nature of the anthraquinone pendants populated on the aliphatic chain. Charging/discharging capability of air batteries was accomplished by using the polymer layer as an organic anode-active material. A test cell fabricated using the conventional MnO(2)/C cathode catalyst exhibited a discharging voltage at 0.63 V corresponding to their potential gap and a charging/discharging cycle of more than 500 cycles without loss of the capacity.     

Biodeterioration of adhesives based on thermoplastic polyurethanes under the action of soil microorganisms

Results of an investigation of the resistance of thermoplastic polyurethanes to the action of biological factors are presented. The mechanism of polyurethane destruction is described. The limiting stage of biostability is shown to be the surface biodeterioration of the material.     

电极界面浓差极化对锂金属沉积的影响

锂金属作为下一代高能量密度电池的理想负极材料受到研究人员广泛关注。然而,锂枝晶生长引起的安全隐患和循环寿命短等问题严重影响了锂金属电池的实用化进程。本文以电化学现象和理论为依据,从浓差极化角度详细分析锂金属电沉积过程中枝晶生长、死锂形成和全电池失效机制,并对目前研究较多的多孔宿主电极中的浓差极化及枝晶抑制进行分析,提出锂金属界面浓差电池现象。本文得到的结论为研究人员更深入地探究锂金属保护策略提供了理论依据。     

Probe beam deflection studies of nanostructured catalyst materials for fuel cells

Probe beam deflection (PBD) techniques, both as cyclic voltadeflectometry (CVD) and chronodeflectometry (CD), were applied for the first time to the study of the electrochemistry of nanostructured Pt materials which are commonly used as electrocatalysts in fuel cells. The electrochemical surface reactions, including faradaic processes, double layer charging and specific anion adsorption were easily detected. Quantitative analysis of the chronodeflectometric data made possible to elucidate the dynamics of double layer charging in such materials and to determine the potential of zero charge (pzc) of the metal present either as a monolithic mesoporous material or as metal nanoparticles supported on carbon. The electro-oxidation of CO, adsorbed on nanostructured Pt, was also studied by CVD and CD being able to detect the formation of CO2 and H3O+ related with the nucleation and growth process which controls the rate of CO stripping. The interplay of Pt oxide formation and COad electrooxidation, both in potential and time, was detected indicating possible application of the technique to other electrocatalysts.     

Heat exchange in granulating thermoplastics

Cooling of polymer granules and strands in air and water was examined. The greatest effect of a turbulence of air flow on the cooling rate of granules was revealed in the starting period. An analysis of the cooling of granules in water demonstrated that the rate of heat transfer from a volume of thermoplastic material to its surface was a rate-limiting step and, thus, an effect of turbulization of a water flow on the cooling was negligible. We showed that it would be appropriate to install partitions destroying a heated boundary layer of water for intensifying process in a cooling bath since an actual cooling of the strands in the water bath longer corresponds to the case when water moves together with strand.     

Termination and water adsorption at the alpha-Al2O3 (012)-aqueous solution interface

Understanding the interaction of water with metal oxide surfaces is important to a diverse array of fields and is essential to the interpretation of surface charging and ion adsorption behavior. High-resolution specular X-ray reflectivity was used to determine the termination of and water adsorption on the alpha-Al2O3 (012)-aqueous solution interface. Interference features in the reflectivity data were used to identify the likely termination, consisting of a full Al2O3 layer plus an additional oxygen layer that completes the coordination shell of the upper aluminum site. This was further investigated through a model-independent inversion of the data using an error correction algorithm, which also revealed that there are two sites of adsorbed water above the surface. Characteristics of these two water sites were quantified through a model-dependent structural refinement, which also revealed additional layering in the interfacial water that gradually decays toward disordered bulk water away from the surface. Although the termination observed in this study differs from that assumed in past studies of surface charging, the density of key surface functional groups is unchanged, and thus, predictions of surface charging behavior are unchanged. As the pH(pzc) of this surface has yet to be modeled accurately, a full 3-dimensional surface structural analysis based on the termination observed in this study is needed so that the effects of surface functional group bond length changes on the pK(a) values can be incorporated. Consideration of the termination and sites of water adsorption suggest that singly coordinated oxygen groups will be the primary sites of ion adsorption on this surface.     

热塑性聚氨酯微孔发泡材料的表观密度与其力学性能的关系

用高压CO2流体通过升温发泡法制备了一系列不同表观密度的热塑性聚氨酯(TPU)微孔发泡材料,探究了TPU发泡材料的表观密度与其力学性能的关系.微孔发泡材料的泡孔结构和表皮结构由扫描电子显微镜表征;不同表观密度材料的力学性能利用万能材料试验机和旋转流变仪表征.研究发现:TPU微孔发泡材料的表观密度主要是由材料皮层厚度占比和泡孔层密度决定的,皮层厚度占比越小和泡孔面积占有率越高,泡沫的表观密度越小;微孔发泡材料在线性应变区的压缩模量E与材料表观密度ρ的关系为:E∝ρ1.7,符合泡沫材料压缩模量与表观密度呈指数关系的基本结论;循环压缩实验中,随微孔发泡材料表观密度减小,损耗百分比增大,残余应变减小;流变实验中,微孔发泡材料的模量随表观密度变化没有明显的变化,阻尼因子tanδ随泡沫表观密度变化不呈单一的规律性.同时,阐明了微孔发泡材料的压缩模量E和损耗百分比随表观密度变化的机理.     

Development of a shear char strength sensing technique to study thermoplastic polyurethane elastomer nanocomposites

Ablative materials, such as thermoplastic elastomer nanocomposites (TPUNs) are used as internal insulation materials for solid rocket motors. These TPUNs are thermoplastic elastomer reinforced by montmorillonite nanoclays, carbon nanofibers, and multi‐walled carbon nanotubes. When these TPUN materials are exposed to an extreme heat flux, a char layer forms along the surface as it ablates. This research aims to use the newly developed shear strength sensor to evaluate the shear strength of this char layer, a characteristic that is important to evaluate ablative materials. This device consists of a method to apply a transverse loading on a test specimen, while measuring the reaction force and the induced strain. This device was used on several types of TPUN test specimens to demonstrate its effectiveness. As a means to determine which ablative exhibited the best performance, the energy of destruction or the energy of dissipation was developed. The maximum force was also accounted for as a secondary quantity for determining the char shear strength. This new shear char strength sensor is fully automated to ensure that each test is repeatable. This guaranteed reliability when collecting the data and eliminated the potential for human error. Copyright © 2017 John Wiley & Sons, Ltd.