Adhesives for Low-Energy Surfaces

Summary: The wetting and adhesive properties of model pressure-sensitive adhesives synthesised by miniemulsion polymerization were investigated. Wetting experiments of aqueous solutions of three different emulsifiers showed that Silwet L-77 (nonionic ethoxylated trisiloxane) was the best wetting agent. Probing adhesive properties, two different structure modifications of the polymer were investigated: a change in the polymer microstructure by the addition of a chain transfer agent and the introduction of a hydrophobic monomer into the polymer backbone. An addition of chain transfer agent was sufficient to obtain a polymer with a significantly different microstructure and, consequently, enhanced adhesion energy but reduced shear resistance. On the other hand, stearyl acrylate (SA) was employed as the hydrophobic monomer and the synthesis was carried out in miniemulsion polymerization which enables the incorporation of hydrophobic compounds without any diffusion limitations. There were almost no differences in the polymer microstructure, whereas, some differences were observed in adhesion properties.     

Nodal Surface Approximations to the Zero Equipotential Surfaces for Cubic Lattices

Models of electrostatic surfaces in atomic crystals rely on equations involving the Jacobi theta functions. Numerical integration of these is prohibitively time consuming, making it difficult to examine the properties of the fields which give rise to the surfaces. We give simple expressions for the key electrostatic surfaces using Fourier expansions in basis sets of nodal surfaces. Any surface may be computed in seconds in a form ammenable to further analysis. The distribution of the mean and Gaussian curvatures over each surface has been visualised by assigning colours so that the range from minimum to maximum value spans blue to red. We similarly explore the mean and Gaussian scalar fields over a range of triply periodic surfaces of the same morphology.     

Organic Reactions at Alumina Surfaces

Recent examples are given to emphasize that alumina can cause many different and often unexpected chemical reactions of adsorbed organic molecules. Recent developments are summarized to publicize that reagent-doped alumina can be used deliberately to achieve some very mild and highly selective organic transformations. The scope and limitations of organic reactions at alumina surfaces are discussed, and the advantages of these heterogeneous reactions over the corresponding homogeneous ones are pointed out. The role of the alumina and future problems are discussed briefly.     

聚合物表面的纳米力学研究

综述了近些年才开展的采用原子力显微技术,在聚合物表面进行纳米力学测量的实验方法和基本理论的进展,内容包括分子链的纳米强度测量,纳米力学各向异性的表征,表面分子间的纳米相互作用,表面形貌的纳米测量以及表面微区的纳米粘弹性研究。     

仿生超疏水性表面的最新应用研究

近年来,除了荷叶表面,更多具有特殊润湿性的动植物表面同样受到关注。通过研究这些表面微观结构,人们成功地仿生制备出各种功能化超疏水表面,从而更好地满足工业中实际应用的需要。该综述简单地介绍了表面润湿的基本模型和最新的几种特殊表面结构,重点介绍近几年仿生超疏水表面应用的最新研究进展,主要包括超疏水表面在超疏油、表面润湿转换、外界刺激下的润湿行为调控、微流体、抗结冰等方面的应用。最后,对超疏水表面研究的未来发展进行了展望。     

Atomic Force Microscopy Analysis of Statistical Roughness of GaAs Surfaces Originated by Thermal Oxidation

We have determined the important statistical quantities of the rough boundary between a GaAs single crystal and its oxide film formed by thermal oxidation. Thermal oxidation of the GaAs surfaces was performed at the temperature of 500°C. Using mathematical procedures developed for treating AFM data consisting of a family of the values of the heights of the irregularities of this roughness the values of the important statistical quantities of roughness were determined for 11 samples of the GaAs surfaces created by dissolution of the thermal oxide films originated during thermal oxidation of the smooth GaAs samples (the times of oxidation of these 11 samples were within interval of 20min–8 hours). From the AFM analysis of the roughness of GaAs surfaces it was found that the roughnening of these surfaces was the most pronounced for shorter oxidation times, i.e. for times smaller than about 2 hours.     

Superhydrophobic PTFE Surfaces by Extension

Summary: A rather simple but yet effective way to achieve a superhydrophobic film by extending a Teflon film is proposed. The water‐contact angle can be increased from 118 to 165° by extending to ca. 190%. The fibrous crystals and the increasing distance between the fibrous crystals are believed responsible for the high water‐contact angle. It indicates that the density of the aligned microstructures is very important for the superhydrophobicity.

Water‐contact angle and the corresponding shapes of water droplets as a function of extension ratio of Teflon tape.     

How Nature Adapts Chemical Structures to Curved Surfaces

Guided by the symmetry in a natural way, periodic potential surfaces partition the space in solid crystalline compounds. The arrangement of atoms, clusters and molecules obviously follows the (in general) curved shape of these ‘space partitioners’. In structures, the atoms therefore choose only a very limited subset of the infinite set of possible positions. In collective structures the periodic surfaces separate areas of different interactions between atoms, clusters, and molecules. In a certain sense, they can be considered as inner surfaces, a knowledge of which reveals insights into the organization of crystalline matter. There are many good indications that the weakly bonded electrons in the highest occupied orbitals are preferably localized in the region of the space partitioners. Dynamic processes as well can be correlated to the shape of the periodic surfaces. Moreover, the surfaces are didactically very helpful in making accessible the complicated three-dimensional relations in collective structures because the main features are projected onto (although curved) two-dimensional creations. The application of periodic potential surfaces to such a variety of compounds as quartz, brass and alpha-amylose underscores their general significance. Simple qualitative considerations already reveal the manifold relations to animate and inanimate nature through to mathematics, art and architecture. It appears that, in a very universal sense, the adaption of structures to a collective order finds a natural solution through curvature.     

从自然到仿生到实际应用的超亲水表面

极端润湿表面一直是表面工程领域的重要研究主题。由于与水具有强烈的吸引力,超亲水表面具有自清洁、防雾等特点,在很多领域都表现出很强的应用潜力。与超疏水表面相比,超亲水表面的研究相对较少,在学术和应用上还存在一些问题。本文介绍了关于超亲水定义的学术争论,分析了超亲水现象的机理,还介绍了超亲水表面的制备方法和实际应用,并指出了超亲水表面存在的问题和研究新动向。本文为超亲水表面的研究提供了一个较为全面/系统的综述。     

非渗透性客体上金属印痕的显现

利用2-(5-溴-2吡啶偶氮)-5-二乙氨基酚显色剂,研究非渗透性客体上金属印痕的显现.考察接触和间隔时间、客体种类和转移次数对显现效果的影响.结果表明,皮肤接触金属工具90 s后,与非渗透性客体接触超过1 s,间隔时间在1～30 d内,转移5次以内时,客体表面遗留印痕均可有效显现.该方法可用以建立起犯罪嫌疑人与金属工...     

On Triply Periodic Minimal Balance Surfaces

Structural Chemistry - A strategy for finding all triply periodic minimal balance surfaces (TPMBS) will be sketched mainly on the basis of fundamental domains of space group pairs of index 2. Some...     

Catalysis Involving Multi-Centered Species on Nonuniform Surfaces, 2. Kinetics

Multi-centered nature of adsorption as well as adsorbate-adsorbate interactions is addressed. A discussed reaction mechanism includes adsorption of a bulky molecule A, which requires several sites for adsorption, and two successive reaction steps of Eley type. Numerical treatment is performed for a special case of this mechanism.     

Preparation of Polylactide Microspheres Having Positively or Negatively Charged Surfaces

The syntheses of polylactides (PLAs) with branched peptide end groups containing reactive (ionic) moieties such as amino or carboxyl groups are described and were used to prepare PLA‐based microspheres (MSs) with positively or negatively charged surfaces. Branched peptides with hydroxyl end groups and four protected amino or carboxyl groups, Boc₄‐K₃‐OH or Bn₄‐E₃‐OH, were synthesized, and the hydroxyl group converted to an alkoxide and was used as the initiation site for the ring‐opening polymerization of L ‐lactide. Subsequent deprotection gave PLAs end‐capped with branched peptides having four amino or carboxyl groups, respectively (K₃‐PLA and E₃‐PLA). K₃‐PLA and E₃‐PLA were converted to K₃⁴⁺‐PLA and E₃^4?‐PLA by acid or base treatment, respectively. MSs with charged surfaces were then prepared using K₃⁴⁺‐PLA or E₃^4?‐PLA as a surfactant [MS(K₃⁴⁺‐PLA) or MS(E₃^4?‐PLA)]. The ionic surface state of the MSs was confirmed by colloidal titration and zeta potential analysis.

SEM image of MSs: MS(K₃⁴⁺‐PLA).     

Three-Dimensional Diabatic Potential Energy Surfaces of Thiophenol with Neural Networks

Three-dimensional (3D) diabatic potential energy surfaces (PESs) of thiophenol involving the S\begin{document}$_0$\end{document}, and coupled \begin{document}$^1$\end{document}\begin{document}$\pi\pi^*$\end{document} and \begin{document}$^1$\end{document}\begin{document}$\pi\sigma^*$\end{document} states were constructed by a neural network approach. Specifically, the diabatization of the PESs for the \begin{document}$^1$\end{document}\begin{document}$\pi\pi^*$\end{document} and \begin{document}$^1\pi\sigma^*$\end{document} states was achieved by the fitting approach with neural networks, which was merely based on adiabatic energies but with the correct symmetry constraint on the off-diagonal term in the diabatic potential energy matrix. The root mean square errors (RMSEs) of the neural network fitting for all three states were found to be quite small (\begin{document}$<$\end{document}4 meV), which suggests the high accuracy of the neural network method. The computed low-lying energy levels of the S\begin{document}$_0$\end{document} state and lifetime of the 0\begin{document}$^0$\end{document} state of S\begin{document}$_1$\end{document} on the neural network PESs are found to be in good agreement with those from the earlier diabatic PESs, which validates the accuracy and reliability of the PESs fitted by the neural network approach.     

聚硼硅氮烷的合成及其流变性能研究

以二氯甲基硅烷、三氯化硼、六甲基二硅氮烷为起始原料,采用缩聚法合成了一种新型SiBNC陶瓷先驱体-聚硼硅氮烷(PBSZ)。通过调节原料二氯甲基硅烷的用量可获得不同软化点的先驱体。通过改进的毛细管流变仪,首次对熔融纺丝状态时聚硼硅氮烷(PBSZ)的流变特性展开了研究。结果表明：PBSZ熔融纺丝时,剪切速率在10～110s-1时,为切力变稀流体。非牛顿指数为0.83～0.90,粘流活化能约为142KJ/mol,表观粘度440～2460Pa·s,PBSZ对温度变化的敏感性较聚碳硅烷小,可纺温区较宽。PBSZ纺丝性能良好,纤维连续无断头长度﹥1600m,纤维直径﹤20μm。     

Wettability of Polyhedral Oligomeric Silsesquioxane Nanostructured Polymer Surfaces

Summary: Some model structures of waterborne polyurethane anionomers containing various amounts (ca. 3–20%) of a diol functionalized polyhedral oligomeric silsesquioxane (POSS) nanofiller were prepared. X‐ray diffraction showed the formation of a nanocrystalline structure in all copolymers considered. Static contact angle measurements indicated a significant enhancement of surface hydrophobicity as well as reduction in surface tension components even at the least POSS level (3%). Dynamic contact angle cycles allowed the evaluation of the hysteresis, which was found to be large and kinetically increasing in POSS‐modified samples. Film topography was analyzed by AFM, showing a more pronounced roughness in the nanostructured surface.

The AFM image showing a moderate roughness increase.