A Facile Method for Preparation of Superhydrophobic Surfaces with Poly(furfuryl Alcohol)/PTFE Composites

A stable superhydrophobic surface have been fabricated with poly(furfuryl alcohol) (PFA)/polytetrafluoroethylene (PTFE) composite coatings on steel substrates by using a facile method. The observation of field emission scanning electron microscopy revealed that the hierarchical microstructures formed on the surfaces are controlled by varying the curing temperature. This method can be easily operated on substrates of steel, therefore is readily developed to other engineering metal substrates such as aluminum, copper, etc.     

氟化铵快速分解－电感耦合等离子体质谱法测定地球化学样品中的稀土元素

测定地球化学样品中的微量稀土元素常用混酸分解法或碱熔融法,这些常规方法往往存在耗费试剂量多、基体效应大、操作周期长等缺点。本文采用氟化铵作熔剂,在旋盖聚四氟乙烯坩埚中220℃熔融样品,后采用2毫升硝酸和0.5毫升高氯酸、硫酸（1+1）在电热板上继续分解,建立了氟化铵分解 －电感耦合等离子体质谱法测定岩石、土壤和水系沉积物中15种微量稀土元素的分析方法。本方法能快速、有效地分解样品,经三种国家标准物质验证（岩石、土壤、水系沉积物）,方法的准确度ΔlgC在0.001～0.02之间,测定值与认定值相符。方法检出限为0.001～0.04μg／g之间,精密度RSD%在1.11％ ～4.85％之间,能够满足微量稀土元素的分析要求,方法具有简单快捷、消耗试剂少、检出限低、精密度与准确度好等特点,适合于地球化学等地质样品微量稀土元素的批量快速分析测定。     

Quantification of particle-bubble interactions using atomic force microscopy: A review

The attachment of particles to bubbles in solution is of fundamental importance to several industrial processes, most notably in the process of froth flotation. During this process hydrophobic particles attach to air bubbles in solution, which allows them to be separated as froth at the surface. The addition of chemicals can help to modulate these interactions to increase the yield of the minerals of interest. Over the past decade the atomic force microscope (AFM) has been adapted for use in studying the forces involved in the attachment of single particles to bubbles in the laboratory. This allows the measurement of actual DLVO (Derjaguin, Landau, Vervey and Overbeek) forces and adhesive contacts to be measured under different conditions. In addition contact angles may be calculated from features of force versus distance curves. It is the purpose of this article to illustrate how the colloid probe technique can be used to make single particle-bubble interactions and to summarise the current literature describing such experiments.     

Heterogeneous continuous flow synthetic system using cyclohexane-based multiphase electrolyte solutions

The discovery that supporting electrolytes can be effectively confined in typical organic solvents in a c-Hex-based multiphase electrolyte solution has led to the development of a novel heterogeneous continuous flow synthetic system. PTFE fiber functions as a separation filter that can efficiently isolate the c-Hex phase from multiphase electrolyte solutions. This system has demonstrated both electrochemical solvating and carbon-carbon bond forming reactions. Hydrophobic substrates can be introduced into the reactor as c-Hex solutions, which are then electrochemically transformed into the target hydrophobic products that pass through the PTFE fiber as c-Hex solutions.     

恒流电晕充电对聚四氟乙烯多孔薄膜驻极体驻极态的影响

利用常温下恒流和恒压电晕充电、充电后的等温表面电位衰减、热刺激放电和扫描电镜等实 验手段研究了恒流和恒压电晕充电技术对聚四氟乙烯多孔薄膜驻极体驻极态的影响.与恒压电晕充电相比较，恒流电晕充电时由于流过薄膜的电流恒定，增加了注入电荷在多孔结构厚度方向界面处的俘获概率，使沉积电荷密度上升，改善了驻极体的储电能力.然而，这些位于不同层深多孔界面处的俘获电荷在这类功能膜储存或使用过程中，经外激发从脱阱位置 以跳动（hopping）模式输运至背电极的路径相对缩短将导致脱阱电荷衰减较快. 关键词： 恒流电晕充电 聚四氟乙烯多孔膜 驻极体 电荷稳定性     

Superhydrophobicity of polytetrafluoroethylene thin film fabricated by pulsed laser deposition

Superhydrophobic polytetrafluoroethylene (PTFE) thin films were obtained by pulsed laser deposition (PLD) technique carried out with KrF excimer laser (λ = 248 nm) of about 1 J/cm² at a pressure of 1.33 Pa. The samples exhibit high water contact angle of about 170° and the sliding angle smaller than 2°. From studying the surface morphology of the prepared films, it is believed that the nano-scale surface roughness has enhanced the hydrophobic property of the PTFE. The increase of trapping air and reducing liquid-solid contact area due to the rough surface, as suggested by the Cassie-Baxter's model, should be responsible for superhydrophobicity of the PLD prepared films. This study thus provides a convenient one-step method without using wet-process to produce a superhydrophobic surface with good self-cleaning properties.     

A new family of low wear,low coefficient of friction polymer blend based on polytetrafluoroethylene and an aromatic thermosetting polyester

To improve the wear resistance of polytetrafluoroethylene (PTFE), a crosslinked aromatic thermosetting polyester (ATSP) has been blended directly with PTFE. Cured ATSP powder which was directly synthesized as a cured powder form was used for this application. Because of the similar processing temperature range of cured ATSP and PTFE, composites within the entire composition range were successfully prepared by blending these two powders using a hot press. Tribological pin‐on‐disk tests (composite pins sliding against gray cast iron disks) showed improvement on friction coefficient of all composites and much less wear than pure PTFE. The composites survived at contact pressures of 7 MPa, which is higher than either pure PTFE or pure ATSP could sustain. With an increase in the amount of ATSP in the composites, storage modulus, and glass transition temperature were higher, and the wear resistance was enhanced. SEM images helped provide explanations for the unusually low mean wear rates that were observed for these composite samples. Copyright © 2008 John Wiley & Sons, Ltd.     

Temperature-dependent ratcheting of PTFE gaskets under cyclic compressive loads with small stress amplitude

Uniaxial stress-controlled ratcheting experiments on PTFE gaskets under cyclic compressive loads with small stress amplitude were performed. The effect of temperature on the deformation behavior was considered. Results showed that the compressive modulus decreases rapidly when the temperature increases from 100 °C to 200 °C. Compressive ratcheting deformation with cycles increase significantly with the increases of temperature. The ratcheting deformations at 100 °C, 150 °C and 200 °C are nearly two, three and five times that at room temperature, respectively. Most of ratcheting deformation mainly occurs during the first 20 cycles because the subsequent ratcheting rate and strain range are small and much less than those in the previous cycles. The accumulated deformation under cyclic loads with small stress amplitude is relatively approach to the static compressive creep with the same peak stress. Therefore, the accumulated deformation with time of PTFE gaskets obtained by cyclic compression with small stress amplitude can be estimated by the corresponding static creep deformation with good accuracy under the approximate stress rate and the same temperature, especially at room temperature.     

The influence of water on the memory effect of the amylose tris(3,5-dimethylphenyl carbamate) stationary phase

Acid/base modifiers are sometimes used as additives in normal phase elution on columns packed with CHIRALPAK^® AD^®. These modifiers affect enantioseparations in ways that are not yet fully understood for the lack of systematic studies. Shifts of the selectivity of certain pairs of enantiomers upon exposure of the column to these modifiers is amply documented. Furthermore, once the modifier has been removed from the mobile phase, the modified selectivity remains, which has been named the Memory Effect. After a column has been exposed to an eluent stream containing acidic/basic modifiers, this particular column no longer separates certain enantiomeric pairs with the same selectivity as a modifier naive column. This makes the transfer of developed methods from one to other CHIRALPAK AD columns difficult to predict, if the selectivity needs to be similar between the two columns. We selected four enantiomeric pairs for a systematic study of this Memory Effect. The selectivity of 4-chlorophenylalanine ethyl ester improves after a solution of ethanesulfonic acid (ESA) is percolated through the column. The selectivity of Propranolol and Tröger's base increases after a solution of Diiospropylamine is percolated through the column. The selectivity of Propranolol and Tröger's base enantiomers is inversely affected by percolation of the acid solution. The 4-chlorophenylalanine ethyl ester enantiomers is inversely affected by percolation of the base solution. In contrast, the selectivity of trans-stilbene oxide (TSO) is not affected by either modifier. Analytical studies of the stationary phase suggest that slow protonation/deprotonation of water molecules attached to the carbamate moiety may be responsible for the acid/base Memory Effect. To further the understanding of the effect of water on the Memory Effect, mobile phases – spiked with water (0.01–0.43%) – were used to measure changes in the Memory Effect. Finally, we showed that the influence of water on the Memory Effect can be minimized by percolating through the column a sufficiently concentrated solution of the appropriate base while using dried mobile phases.     

Surface‐initiated atom transfer radical polymerization from porous poly(tetrafluoroethylene) membranes using the C?F groups as initiators

This work reports the surface‐initiated atom transfer radical polymerization (ATRP) from hydrogen plasma‐treated porous poly(tetrafluoroethylene) (PTFE) membranes using the C? F groups as initiators. Hydrogen plasma treatment on PTFE membrane surfaces changes their chemical environment through defluorination and hydrogenation reactions. With the hydrogen plasma treatment, the C? F groups of the modified PTFE membrane surface become effective initiators of ATRP. Surface‐initiated ATRP of poly(ethylene glycol) methacrylate (PEGMA) is carried out to graft PPEGMA chains to PTFE membrane surfaces. The chain lengths of poly(PEGMA) (PPEGMA) grafted on PTFE surfaces increase with increasing the reaction time of ATRP. Furthermore, the chain ends of PPEGMA grown on PTFE membrane surfaces then serve as macroinitiators for the ATRP of N‐isopropylacrylamide (NIPAAm) to build up the PPEGMA‐b‐PNIPAAm block copolymer chains on the PTFE membrane surfaces. The chemical structures of the modified PTFE membranes are characterized using X‐ray photoelectron spectroscopy. The modification increases the surface hydrophilicity of the PTFE membranes with reductions in their water‐contact angles from 120° to 60°. The modified PTFE membranes also show temperature‐responsive properties and protein repulsion features owing to the presence of PNIPAAM and PPEGMA chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2076–2083, 2010