超薄聚合物表面与滴状冷凝的研究

采用等离子体聚合技术在黄铜管外表面制备了六氟丙烯、六甲基二硅氧烷的超薄聚合物薄膜,实现了水蒸气的滴状冷凝.对不同冷凝表面的传热性能进行了实验测定,并对聚合膜的表面性能进行了测试和估算.分析讨论了聚合工艺条件对滴状冷凝传热及膜与基材粘着性能的影响.     

Ni-P化学镀层表面实现滴状冷凝传热

为了探索能实现滴状冷凝传热的表面制备技术,采用化学镀技术在碳钢表面制备非晶态Ni-P化学镀层,对其冷凝传热性能进行了实验研究。结果表明,Ni-P化学镀层表面常压水蒸气下实现了完全的滴状冷凝传热,表面热通量和传热系数均比膜状冷凝Nusselt理论计算结果提高了3～5倍。同时发现,镀层的非晶态是实现滴状冷凝传热形态的主要原因,经过热处理晶化后,表面形成的是滴膜共存的冷凝传热形态,冷凝传热强化效果显著降低。     

超薄PTFE表面上滴状冷凝的传热研究

采用离子束动态混合注入技术 ( Dynamic Ion- beam Mixed Implantation)制备了铜基、不锈钢基聚四氟乙烯 ( PTFE)的超薄聚合物薄膜 ,实现了水蒸汽的滴状冷凝。对不同冷凝表面的传热特性进行了试验测定。分析讨论了试验表面制备工艺条件及表面材料导热系数对滴状冷凝传热性能的影响。     

聚合物表面性能对强化冷凝传热的影响

对离子束动态混合注入(DIMI)技术制备的黄铜、紫铜、不锈钢和碳钢管基聚四氟乙烯(PTFE)表面的冷凝传热实验发现,用不同加工条件制备的表面具有不同的化学组成、不均匀的表面状态以及不同的物理化学性质,从而导致不同的冷凝成滴面积和传热性能,而且表面加工条件对滴状冷凝传热的寿命有至关重要的作用,不同基体材料应有不同的最佳制备工艺条件.不同工艺条件下制备黄铜基PTFE表面水蒸气竖直管外冷凝传热通量比相应的膜状冷凝提高0.3-4.6倍,冷凝传热系数提高1.6-28.6倍.实验结果也表明冷凝表面基体材料对冷凝传热性能有一定的影响.     

聚四氟乙烯薄膜表面滴状冷凝传热实验研究

为了探索实现滴状冷凝传热的新表面涂层 ,采用离子束动态混合注入技术制备了紫铜基聚四氟乙烯(PTFE)薄膜 ,显著地提高了水蒸气冷凝传热性能。实验表明 ,该表面涂层能够实现常压水蒸气稳定的滴状冷凝形态 ,在表面过冷度 9.8— 1 4 .2K范围内 ,滴状冷凝传热通量和传热系数比膜状冷凝结果提高 30—47倍。同时发现 ,在大气压附近 ,热通量和冷凝传热系数都随着水蒸气蒸汽温度的增加而增加 ,但表面过冷度随蒸气温度增加呈弱增加趋势     

超疏水表面蒸汽及含不凝气蒸汽滴状冷凝传热实验分析

通过紫铜基表面上制备两种具有微纳米结构的超疏水表面以及相同化学修饰的光滑疏水表面,实验研究了各表面上空气环境下水的润湿特性以及在纯蒸汽、蒸汽-空气混合气体环境下,表面的滴状冷凝传热特性和冷凝液滴的运动和润湿特性。结果表明:纯蒸汽滴状冷凝条件下,超疏水表面的传热性能明显低于光滑疏水表面的传热性能;含低浓度不凝气蒸汽冷凝环境下,超疏水表面传热性能与光滑疏水表面相近;蒸汽冷凝环境中,超疏水表面上液滴的接触角明显低于其在空气条件下接触角,并且接触角滞后增大。分析得到,微纳米结构的存在使冷凝过程液滴的接触角滞后增大,微纳米结构中冷凝液滞留增加的壁面热阻等抑制了滴状冷凝传热性能;并提出了蒸汽及含不凝气蒸汽冷凝环境中液滴在超疏水表面上的润湿模式。     

实现滴状冷凝新途径的研究——(Ⅰ)基本概念及实验结果

本文从表面科学的角度出发,对目前实现滴状冷凝的各种方法进行了评述.提出了实现滴状冷凝的新途径,并通过实验研究确认其可行性.在不锈钢和紫铜两种圆管外表面上,采用了不同的表面处理技术进行处理.对每种表面都做了垂直管外的水蒸汽冷凝实验.在几种表面上,获得了稳定的滴状冷凝,并整理出各种表面的传热实验结果及滴状冷凝照片.对成滴表面的特性,进行了分析与探讨.     

实现滴状冷凝新途径的研究——(Ⅲ)滴状冷凝传热系数的测定和寿命实验

采用直接测温的方法,测定了新表面材料的滴状冷凝传热特性,并同国外滴状冷凝传热研究的结果进行比较.分析讨论了Cu-Cr表面和机械抛光表面传热性能的差异.对Cu-Cr和机械抛光两种表面进行了寿命实验,滴状冷凝现已超过8500小时.     

滴膜共存表面强化冷凝传热

<正>滴状冷凝具有很高的传热速率,其冷凝传热系数是膜状冷凝的几倍至几十倍,但是,由于长期维持滴状冷凝表面制备技术的限制,该技术距工业化应用还有一定的距离,在滴状冷凝的研究过程中,经常发现滴膜共存冷凝现象,而且传热系数较普通的膜状冷凝有较大的提高,在以往的实验研究中,往往不能肯定地排除蒸汽中有机杂质的影响,滴膜共存表面的实验研究也间接地证实了蒸汽中是不含有机杂质的,滴膜共存表面也是强化冷凝传热很实用的技术,是滴状冷凝传热过程全面工业化的过渡阶段.所以,研究滴膜共存表面强化冷凝传热的特性具有重要的理论意义和实用价值.Kumagai等报道了在竖平面上垂直分割的滴膜共存表面上冷凝传热的实验.结果表明,当滴状冷凝区和膜状冷凝区的面积比为1:1时,平均热负荷要高于在通常表面上滴状冷凝和膜状冷凝热负荷的算术平均值,而且平均热负荷与表面分割方式和分割数目有关.他们在一种特殊分割形式的表面上得到的最大热负荷高于当全部表面为滴状冷凝时的最大热负荷.     

金属基底超疏水表面制备技术发展及滴状冷凝强化传热应用展望

蒸汽冷凝过程在石油化工领域有着广泛的应用,滴状冷凝传热模式相比于传统的膜状冷凝方式其传热系数与传热效率大大提高,可作为节约能源和高效利用资源的重要手段。随着金属基底超疏水表面制备技术的发展,蒸汽滴状冷凝研究的不断深入,为滴状冷凝强化传热在工业上应用提供了理论依据和制备方法。介绍了近年来金属基底超疏水表面制备技术发展,评述各方法的特点,提出滴状冷凝强化传热工业化应用所面临的问题。     

Plasma polymerized ferrocene films

This communication describes the formation of high index of refraction polymer thin films using a novel plasma polymerization deposition process. A flowing afterglow plasma reactor was modified to enable sublimation of solid samples into the gas phase for subsequent plasma polymerization. Thin films of plasma polymerized ferrocene were deposited on substrates and subsequently characterized. The refractive index as a function of processing conditions was obtained. Relatively high values of n (∼1.73 at 589 nm) were obtained. The chemical nature of the polymer thin films was characterized using FTIR and XPS spectroscopy. This work demonstrates that plasma polymerization is an enabling technology for the fabrication of photonic thin films that utilize solid state precursors.     

Cohesive Zone Models of Polyimide/Aluminum Interphases

The fracture energy required to delaminate PMDA/ODA polyimide films from aluminum substrates was determined using the circular blister test. Films were prepared by spin coating the polyamic acid of PMDA and ODA onto polished aluminum substrates, by vapor co-deposition of PMDA and ODA monomers onto polished aluminum substrates, or by spin-coating the polyamic acid onto polished aluminum substrates that were first coated with thin layers of γ-aminopropyltriethoxysilane (γ-APS). Elastic and elastoplastic analyses were used to extract the fracture energies from the blister test results. Elastoplastic analysis provided fracture energies that ranged from 579 J/m² for spin-coated films on polished substrates to 705 J/m² for vapor-deposited films on polished substrates and to 750 J/m² for spin-coated films on silanated substrates. These values were intermediate between those provided by the two different elastic analyses. Differences in fracture energy determined by the three different analysis methods were related to plastic deformation in the films and, in the case of the two elastic analyses, to differences in the approach used to extract the fracture energy from experimental results. Failure of specimens prepared by spin-coating PMDA/ODA films onto aluminum substrates occurred cohesively within the polymer, near the interface between well imidized polymer in the bulk of the films and poorly imidized polymer in a layer near the aluminum surface. For the case of specimens prepared by vapor codeposition of PMDA and ODA monomers, failure occurred within the vapor deposited films, close to the aluminum/film interface. Failure of spin-coated films on silanated substrates occurred mostly within the γ-APS but leaving 'islands' of polyimide and silane on the aluminum.     

Cohesive Zone Models of Polyimide/Aluminum Interphases

The fracture energy required to delaminate PMDA/ODA polyimide films from aluminum substrates was determined using the circular blister test. Films were prepared by spin coating the polyamic acid of PMDA and ODA onto polished aluminum substrates, by vapor co-deposition of PMDA and ODA monomers onto polished aluminum substrates, or by spin-coating the polyamic acid onto polished aluminum substrates that were first coated with thin layers of γ-aminopropyltriethoxysilane (γ-APS). Elastic and elastoplastic analyses were used to extract the fracture energies from the blister test results. Elastoplastic analysis provided fracture energies that ranged from 579 J/m² for spin-coated films on polished substrates to 705 J/m² for vapor-deposited films on polished substrates and to 750 J/m² for spin-coated films on silanated substrates. These values were intermediate between those provided by the two different elastic analyses. Differences in fracture energy determined by the three different analysis methods were related to plastic deformation in the films and, in the case of the two elastic analyses, to differences in the approach used to extract the fracture energy from experimental results. Failure of specimens prepared by spin-coating PMDA/ODA films onto aluminum substrates occurred cohesively within the polymer, near the interface between well imidized polymer in the bulk of the films and poorly imidized polymer in a layer near the aluminum surface. For the case of specimens prepared by vapor codeposition of PMDA and ODA monomers, failure occurred within the vapor deposited films, close to the aluminum/film interface. Failure of spin-coated films on silanated substrates occurred mostly within the γ-APS but leaving ‘islands’ of polyimide and silane on the aluminum.     

Continuous infrared‐assisted double‐sided roll‐to‐roll embossing of flexible polymer substrates

This article reports a novel infrared (IR)‐assisted roll‐to‐roll embossing method, which enables the replication of microfeatures onto the surfaces of flexible polymer substrates. An IR‐assisted roll‐to‐roll embossing facility was designed and built in our laboratory especially for this study. Metallic rollers bearing micropatterns of two different feature sizes, namely 150 and 20 μm in depth, were employed. The former one was prepared by microelectric discharge machining the roller, whereas the latter was fabricated by electroplating a thin layer of nickel on the surface of the roller, followed by a diamond turning process to create the microstructures. The embossing facility was used to replicate the microstructure onto polyethylene terephthalate and polycarbonate films in the experiments. During roller embossing, the IR radiation shed on the rollers, and the energy was converted into heat to melt the polymer substrates and to replicate the microstructures. The influence of various processing parameters on the replicability of microfeatures was investigated. Under the proper processing conditions, double‐sided flexible polymer substrates with microstructures could be successfully fabricated. The proposed method shows great potential for fabrication of micro‐optical components due to its simplicity and versatility. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Adhesion between polymer substrates and plasma films from tetramethylsilane and tetramethyltin by glow discharge polymerization

Adhesion between various polymer substrates and plasma films, which had been prepared from either tetramethylsilane or tetramethyltin by glow discharge polymerization and deposited on the surface of the polymer, was evaluated by the Scotch tape test and by lap-shear strength. It was found that the plasma films exhibited fairly good adhesion to the polymer substrates (with the exception of polypropylene). The position where failure occurred was determined by X-ray fluorescence analysis, scanning electron microscopy and energy diffractive X-ray analysis. This position was at an inner layer of the plasma film (cohesive failure of plasma film), within the polymer substrate (material failure of polymer) or at the interface between polymer substrate and plasma film (adhesive failure) depending upon the polymer substrate. These results indicate an important aspect of durability of surface modification by glow discharge polymerization.     

Substrate thickness: An effective control parameter for polymer thin film buckling on PDMS substrates

Buckling patterns of polymer thin films on plasma‐treated poly(dimethylsiloxane) (PDMS) substrates were sensitively affected by the thickness of the substrate in addition to the substrate modulus. On highly crosslinked PDMS substrates, the buckling wavelength of polymer thin films sharply increased as the thickness of the substrates were raised and approached a plateau value when the substrate was 2.5 mm‐thick. On weakly crosslinked PDMS substrates, the wavelength still increased even when the substrate was thicker than 20 mm. The high dependence of the buckling on the substrate thickness has not been reported before and is unexpected from the current predictions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preliminary experiment of surface hardening of polymers by glow discharge polymerization

Polymers including polyethylene, polycarbonate, and polytetrafluoroethylene were modified by glow discharge polymerization to enhance surface hardness. The surface hardness of the polymer substrates could be improved by glow discharge polymerizations of silicon-containing compounds. The mixture of tetramethylsilane (TMS) and oxygen was more effective than tetramethoxysilane to improve the surface hardness. The surface hardness improved by the glow discharge polymerization strongly depended on the nature of the polymer substrates to be modified. The adhesion between polymer films prepared from the TMS/O₂ mixture by glow discharge polymerization and the polymer substrates was good.     

基片对超导厚膜性能的影响

采用普通丝网印刷技术在YSZ基片上制得零电阻温度力90K、转变宽度为2K、与基片能良好附着、具有良好工艺性的Y-Ba-Cu-O系超导厚膜。运用四探针法测量电阻,X-射线衍射仪,电子显微镜分析晶相组成和显微结构,用扫描电镜和电子能谱分析技术研究了膜与基片间的反应,发现不同基片(Al_2O_3和YSZ)、膜与基片之间的反应不同,对膜相结构、致密情况的影响不同,因而厚膜的超导电性能也就不同。     

PEDOT:PSS coating on specialty papers: Process optimization and effects of surface properties on electrical performances

In this study, the effects of different paper substrates on the electrical resistance of conducting polymer films are reported. A novel method of bar coating is used for the fabrication of organic conductive films on various substrates. Solutions to improve the continuity of conductive thin film in order to enhance the electrical properties are demonstrated. In order to compare the capability of these different substrates for a potential use in the organic electronic field, sheet resistance measurements were made. It is emphasized that substrate roughness and surface energy are two fundamental parameters, due to their significant impact on sheet resistance. Two methods to overcome bad paper surface properties are proposed. The first consists in the superimposition of conductive polymer layers and the second in the use of a protective layer.     

Electro-optical properties of the normally transparent type anisotropic polymer dispersed liquid crystal films

We fabricate normally transparent type of polymer dispersed liquid crystal (PDLC) films, which are composed of nematic liquid crystals in anisotropic polymer network. The glass substrates of the films are treated with rubbing such that the polymer and liquid crystal molecules are plane parallel aligned in the sample cell. The liquid crystals used are 5CB and 7CB. The polymer is cured at a variety of UV wavelengths and intensities. The electro-optical properties of these PDLC films are reported. This type of transparent PDLC shows an improvement in the transparency of the clear state and a decrease in the driving voltage.