Synthesis and characterization of novel polyimides containing stilbene unit in the side chain and their controllability of nematic liquid crystal alignment on the rubbed surfaces

Four polyimides containing hexylene spacer and a fluorostilbene unit in the side chains were prepared in thin‐film form by two‐step condensation of 3,3′‐bis[(4′‐fluoro‐4‐stilbenyl)oxyhexyloxy]‐4,4′‐biphenyldiamine (FS6B) with pyromellitic dianhydride (PMDA), benzophenone‐3,3′,4,4′‐tetracarboxylic dianydride (BTDA), 4,4′‐oxydi(phthalic anhydride) (ODPA), and 4,4′‐hexafluoroisopropylidenedi(phthalic anhydride) (6FDA), respectively, and their controllability of liquid crystal (LC) alignment on rubbed surfaces was investigated. Pretilt angles of LCs were achieved in the 2–9° range, depending on the rubbing density and backbone structures. The effect of the mesogenic stilbene group on the pretilting of LCs was distinctive in FS6B‐PMDA. Contact‐angle measurements on thin films annealed at 120 °C revealed that FS6B‐PMDA potentially had the better alignment stability than FS6B‐6FDA. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3622–3632, 2001     

一种荷叶效应涂层的制备

Composite coatings with lotus effect were fabricated via imbedding micro-silica and then nano-silica. The micro-silica and nano-silica was subsquently fixed on the surface to form hierarchical micro- and nano-structures, and at the same time, the epoxy resin modified by low surface free energy material was coated on the coatings. The staic contact angle of the coatings is as high as 165° and the tilt angle for 6.5 μL water droplet is as low as 2.5°. The coatings show the similar hydrophobic capability and structure to lotus leaves.     

Physical significance of contact angles

Summary The physical significance of contact angles has been interpreted on the basis of a model derived from known surface energy relationships. The degrees of non-spreading and spreading have been expressed in terms of the magnitude of contact angles. On the basis of the physical picture, hysteresis of contact angle has been calculated from the experimental values of equilibrium contact angle and surface tension of the liquid. It has been suggested that it is not necessary to assume that hysteresis of contact angles is due to surface roughness of solids. The picture also explains why apparent contact angle on a non-flat solid surface is more than that on a flat solid.With 2 figures and 1 table     

超疏水性生物表面的研究进展

介绍了几种天然超疏水生物表面的研究进展,包括蛾翅膀、蝉翼、蝴蝶翅膀、白蚁翅膀、甲虫,蚊子的腿、翅及其复眼,水黾的腿部和荷叶的表面。 对现有的仿生超疏水材料的制备方法及常用作表面修饰的低表面能材料做了简单的归纳与总结。 对超疏水材料研究面临的挑战及以后的发展趋势做了展望。     

Low‐rate dynamic contact angles on poly(methyl methacrylate/ethyl methacrylate, 30/70) and the determination of solid surface tensions

Low‐rate dynamic contact angles of 12 liquids on a poly(methyl methacrylate/ethyl methacrylate, 30/70) P(MMA/EMA, 30/70) copolymer were measured by an automated axisymmetric drop shape analysis‐profile (ADSA‐P). It was found that five liquids yield nonconstant contact angles, and/or dissolve the polymer on contact. From the experimental contact angles of the remaining seven liquids, it is found that the liquid–vapor surface tension times cosine of the contact angle changes smoothly with the liquid–vapor surface tension (i.e., γ_l|Kv cos θ depends only on γ_l|Kv for a given solid surface or solid surface tension). This contact angle pattern is in harmony with those from other methacrylate polymer surfaces previously studied.^45,50 The solid–vapor surface tension calculated from the equation‐of‐state approach for solid–liquid interfacial tensions¹⁴ is found to be 35.1 mJ/m², with a 95% confidence limit of ± 0.3 mJ/m², from the experimental contact angles of the seven liquids. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2039–2051, 1999     

Covalently Attached Liquids: Instant Omniphobic Surfaces with Unprecedented Repellency

Recent strategies to prepare “omniphobic” surfaces have demonstrated that minimizing contact angle hysteresis (CAH) is the key criterion for effectiveness. CAH is affected by chemistry and topography defects at the molecular and higher levels, thus most surfaces exhibit significant CAH. Preparative methods for stable coatings on smooth substrates with negligible CAH (<2°) for a broad range of liquids have not been reported. In this work, we describe a simple and rapid procedure to prepare omniphobic surfaces that are stable under pressure and durable at elevated temperatures. Consistent with theory, they exhibit sliding angles that decrease with liquid surface tension. Slippery omniphobic covalently attached liquid (SOCAL) surfaces are obtained through acid‐catalyzed graft polycondensation of dimethyldimethoxysilane. The smooth, stable, and temperature‐resistant coatings show extremely low CAH (≤1°) and low sliding angles for liquids that span surface tensions from 78.2 to 18.4 mN m^?1.     

超疏水表面的研究进展

表面的浸润性是决定材料应用的一个重要性质,许多物理化学过程,如吸附、润滑、黏合、分散和摩擦等均与表面的浸润性密切相关.近年来,由于超疏水表面在自清洁表面、微流体系统和生物相容性等方面的潜在应用,有关超疏水表面的研究引起了极大的关注.本文综述了超疏水表面研究的新进展:简单介绍了表面浸润性的表征手段和影响因素,归纳了超疏水表面的制备方法和相关的理论分析,对超疏水表面研究的发展进行了展望.     

仿荷叶表面研究进展

近年来,荷叶表面的自清洁功能引起人们极大的研究兴趣,这种自清洁功能源自于表面形貌与低表面能物质的共同作用.目前,已用不少方法来制备仿荷叶表面.本文回顾近年来仿荷叶表面研究成果,探讨仿荷叶表面研究与发展趋势.     

柱状结构阵列碳纳米管膜的超疏水性研究

浸润性是固体表面的重要性质之一 .决定固体表面的浸润性的两个主要因素中 ,化学性质是内因 ,而几何结构形貌也是不可缺少的重要因素 .通过改变固体表面的粗糙度可以改变其浸润性 [1～ 5] .通常 ,人们用水接触角的大小来衡量固体表面水的浸润性 ,水与固体表面的接触角大于 1 5     

具有微纳米结构超疏水表面润湿性的研究

本文综述了近年来具有微纳米结构超疏水表面的研究进展。介绍了具有微纳米结构超疏水表面的制备方法,表面结构对超疏水性能的影响,周期性结构表面超疏水的条件,超疏水表面接触角滞后以及功能化超疏水表面等方面的研究,探讨了这一领域存在的问题及可能的发展方向。     

二氧化硅／环氧树脂复合涂层的制备及其疏水性能

采用喷涂技术,在马口铁表面喷涂环氧树脂和二氧化硅复合涂层,研究了二氧化硅的含量对表面疏水性的影响,复合涂层的疏水性随二氧化硅含量的增加而增加．当二氧化硅质量分数增大到40％时,所制备的复合涂层与水的接触角约为141°且具有较小的滚动角．     

用对称透射二维WAXS强度研究PET取向非晶态结构

用对称透射法，测试聚酯（ＰＥＴ）取向非晶试样的二维广角Ｘ射线散射相干强度Ｉ（Ｋ，α），将不同方位角α上的Ｉ（Ｋ，α）非晶重叠峰曲线进行计算分解，获得分子链间原子散射引起的二个峰为Ａ（Ｋ＝０．１２６），Ｂ（Ｋ＝０．１６９），分子链内原子散射引起五个峰分别为Ｃ（Ｋ＝０．３０４），Ｄ（Ｋ＝０．５５３），Ｅ（Ｋ＝０．３７４），Ｆ（Ｋ＝０．４６５），Ｇ（Ｋ＝０．６０６），Ｋ单位为ｎｍ＾－１，分析了它们的结构     

Dynamic behavior of polymer surface and the time dependence of contact angle

The increased attention has been focused on the re-searches of soft materials proposed by Pierre-Gilles de Gennes, a Nobel Prize Laureate in Physics. A special issue of “Science” on soft surfaces was published in 2002 to review specific surface properti…     

BPDA/PPD/OTOL聚酰亚胺纤维的力学性能、形貌和结构

在3,3’,4,4’-联苯四酸二酐(BPDA)和对苯二胺(PPD)体系中引入3,3’-二甲基联苯胺(OTOL),显著改善了纤维的力学性能。当n(PPD)∶n(OTOL)=70∶30时,纤维的拉伸强度可达到改性前的2倍,其拉伸强度和拉伸模量分别为1.50和80 GPa。SEM照片显示了纤维的断面为圆形且没有孔穴,也没有明显的"皮芯"结构和原纤结构。WAXD和SAXS分析表明,纤维的轴向堆积和分子链取向在热牵伸过程中得到改善。     

Polarized SERS Controlled by Anisotropic Growth on Ordered Curvature Substrate

Colloidal lithography is an efficient and low-cost method to prepare an ordered nanostructure array with new shapes and properties. In this study, square-shaped and cone-shaped Au nanostructures were obtained by 70° angle deposition onto polystyrene bead array with the diameter of 500 nm when a space of 120 nm is created between the neighbor beads by plasma etching. The gaps between the units decrease when the Au deposition time increases, which leads to the polarized enhanced local field, in agreement with the surface-enhanced Raman scattering spectra (SERS) observations and finite-difference time-domain (FDTD) simulations. When the Au deposition time increased to 5 min, 5 nm gaps form between the neighbor units, which gave an enhancement factor of 5 × 10⁹. The SERS chip was decorated for the detection of the liver cancer cell marker Alpha-fetoprotein (AFP) with the detection limit down to 5 pg/mL.     

Optimal flip angle for robust practical quantitative NMR measurement using a fixed pulse length

NMR quantification has been traditionally performed by using internal standards. Although methods using external reference in NMR quantification have been developed, the major obstacles in using external referencing method are the measurement deviations associated with changing sample conditions and the requirement of pulse width calibration for every sample in order to compensate these errors. The calibration process is time consuming and in some cases impossible. We developed a quantitative NMR method fixed pulse length (FIXPUL) for all measurements without sample-by-sample calibration. The method is based on the use of an optimal flip angle calibrated for an external standard so that the quantitative errors associated with the pulse width variations are minimized. FIXPUL can be implemented on most basic NMR spectrometers and is robust and easily automated. The method is applicable to a wide range of solution NMR samples in chemistry, biology, and drug research and discovery.     

Small angle scattering of partially oriented polymers

Summary A general method for the calculation of the small angle scattering pattern of partially oriented polymers with rotational symmetry about the fiber axis is explained. The method can be used with widely varying models for the basic scattering unit.

---

Zusammenfassung Es wird eine allgemeine Methode zur Berechnung des Kleinwinkelstreudiagramms von partiell orientierten Polymeren mit Rotationssymmetrie bezüglich der Faserachse angegeben. Als Modell für die streuende Grundeinheit können die verschiedensten Strukturen verwendet werden.