Film instability induced evolution of hierarchical structures in annealed ultrathin films of an asymmetric block copolymer on polar substrates

With an atomic-force microscope and a grazing-incidence small-angle X-ray scattering we studied ex situ the evolution of hierarchical structures in isothermally annealed ultrathin films of asymmetric polystyrene-block-poly(methyl methacrylate) P(S-b-MMA) that dewetted on polar substrates via a mechanism involving nucleation and growth. Film instability causes the surface to acquire an undulating thickness through incommensurability, producing not only the relief structures on a micrometer scale but also mesophase-separated domains on a nanometer scale. The dewetted morphologies strongly influence the ordering behavior of the nanoscale domains. The noncylindrical nanostructures become stable at the curved edges of the relief microstructures in the destabilized P(S-b-MMA) films, for which a preferential wetting of the PS block with the free surface is prohibited. Additionally, the shape of relief structures as result of film instability correlates with the formation of mesophase-separated nanodomains. At early stages of film instability, the formation of parallel-oriented PMMA cylindrical nanodomains increases the deformation energy and it further persists to force the shape of relief structures between irregular holes to have a facet-wedge shape. However, those relief structures are expected to be not at equilibrium. At high temperatures, the relief structures between irregular holes progressively developed to form hemispherical-cap drops accompanied by a transformation of cylindrical into noncylindrical nanodomains at curved surfaces.     

How to manipulate the electrospinning jet with controlled properties to obtain uniform fibers with the smallest diameter?—a brief discussion of solution electrospinning process

Solutions of five different polymers, namely, polystyrene (PS), polyacrylonitrile (PAN), polyhydroxybutrate (PHB), poly(D-L-lactic acid) (PLA), and Nylon6, were used to investigate their rheological properties on the electrospinnability. In order to effectively reduce the diameter of electrospun fibers, polymers with higher molecular weights (MW) were needed to develop entangled solutions at much lower concentrations and with viscosities as low as that of a pure solvent. A minimum polymer concentration 1.0–2.0 times larger than the entanglement concentration was required to prepare the bead-free fibers. Using this strategy, uniform PS fibers with the lowest ever diameter of ∼15 nm were successfully obtained using an MW of 3 × 10⁷ g/mol at a concentration of 0.1 vol.%. For a given electrospinning solution, processing variables of low flow-rate (Q) and high voltage (V) were desirable in obtaining fibers with small diameters. However, Q and V were correlated by a power law relation: V∼Q ^a, wherein the exponent a had a value of 0.1–0.4, which was relevant with the solution types. Based on the finite element analysis (FEA), a significant measure of electric field (E) occurred around the needle tip used in the experiment, and its magnitude decayed with increasing distance from the needle end (z): E∼z ⁻ⁿ. The exponent n was 1.0–2.0, depending on the needle–plate geometry, i.e., needle length, needle diameter (D _o ), plate diameter, and tip-to-plate distance (H). According to FEA results, H exhibited negligible effects on the electric field in the region of interest, i.e., z/D _o ∼1 to 10. Due to the presence of high measures of E at the needle end, approaches to render a shorter and thinner straight jet issuing from the Taylor cone to yield thinner fibers were sought because a more significant jet stretching in the “jet whipping region” can take place. A feasible route to predict the as-spun fiber diameter produced by the manipulation of the electrified jet is provided by experimentally measuring the jet diameter and numerically calculating the electric field for the jet whipping process.     

Highly transparent and organosoluble polyimides derived from 2,2′‐disubstituted‐4,4′‐oxydianilines

Polypyrrole (PPy) and Polypyrrole‐ZnO (PPy‐ZnO) nanocomposites were electrodeposited on mild steel and its corrosion protection ability was studied by Tafel and Impedance techniques in 3.5% NaCl solution. Pure Polypyrrole film was not found to protect the mild steel perfectly but the coating with nano‐sized ZnO (PPy‐ZnO) has dramatically increased the corrosion resistance of mild steel. Electrochemical Impedance Spectroscopy (EIS) measurements indicated that the coating resistance (R_coat) and corrosion resistance (R_corr) values for the PPy‐ZnO nanocomposite coating was much higher than that of pure PPy coated electrode. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

石佳矿山高边坡崩塌特征与失稳模式分析

高位崩塌灾害是矿山典型且频发的地质灾害,常常导致巨大的经济损失甚至人员伤亡.本文以河津市石佳矿山为研究对象,基于已有地质资料和现场调查情况,分析崩塌发育特征以及失稳模式类型,并通过Rocfall模拟危岩体失稳过程.研究结果表明:研究区受采矿扰动形成高陡裸露岩质边坡,陡倾裂隙发育,在差异风化作用下危岩体将达到极限状态,最...     

Development of a gel spinning process for high‐strength poly(ethylene oxide) fibers

This article describes a new gel‐spinning process for making high‐strength poly(ethylene oxide) (PEO) fibers. The PEO gel‐spinning process was enabled through an oligomer/polymer blend in place of conventional organic solvents, and the gelation and solvent‐like properties were investigated. A 92/8 wt% poly(ethylene glycol)/PEO gel exhibited a melting temperature around 45°C and was highly stretchable at room temperature. Some salient features of a gel‐spun PEO fiber with a draw ratio of 60 are tensile strength at break = 0.66 ± 0.04 GPa, Young's modulus = 4.3 ± 0.1 GPa, and a toughness corresponding to 117 MJ/m³. These numbers are significantly higher than those previously reported. Wide‐angle x‐ray diffraction of the high‐strength fibers showed good molecular orientation along the fiber direction. The results also demonstrate the potential of further improvement of mechanical properties. POLYM. ENG. SCI., 54:2839–2847, 2014. © 2014 Society of Plastics Engineers     

Estimation of illuminant chromaticity based on highlight detection for face images with varying illumination

Illuminant chromaticity estimation is required in the fields of the tracking and recognition of human faces, compensation and detection of skin color, image reproduction, and color constancy. This article proposes a simple and effective method to estimate the illuminant chromaticity using highlights from the face region. We first select the candidate points through the detection of highlights around the leftmost pixel of the rg chromaticity space from the facial images under various illuminant conditions and then estimate the illuminant chromaticity by averaging the chromaticities of the candidate points. To enhance the illuminant chromaticity estimation accuracy, we propose a more elaborate estimation method, which effectively readjusts the candidate points of the highlight regions according to the conditions derived from two ethnic and three illuminant groups. The experiment results show that our proposed method reliably estimates the illuminant chromaticity under various color temperatures and illuminant directions. © 2012 Wiley Periodicals, Inc. Col Res Appl, 39, 188–199, 2014     

Intensify the application of ZnO-based nanodevices in humid environment: O2/H2 plasma suppressed the spontaneous reaction of amorphous ZnO nanowires

In this work, we have demonstrated that amorphous ZnO nanobranches (a-ZnO NBs) could spontaneously react from the crystalline ZnO NWs (c-ZnO NWs) at specific humid environment. The spontaneous reaction mechanism and result can be analyzed by humidity controlling and optical microscope (OM)/scanning electron microscope (SEM)/Kelvin probe force microscopy (KPFM)/transmission electron microscopy (TEM) system. We can make the c-ZnO NWs spontaneous reaction happen at different humid environments and suppress the a-ZnO NBs spontaneous reaction by oxygen/hydrogen plasma surface passivation. The hydrogen plasma surface treatment also can improve the UV sensing sensitivity more than twofold. This work provides the mechanism and methods of the a-ZnO NBs spontaneous growth and offers the passivation treatment for strengthening and enhancing ZnO-based nanodevice application in humid environment and UV light detection, respectively.     

Microstructure and characterization of electrospun poly(vinyl alcohol) nanofiber scaffolds filled with graphene nanosheets

Graphene nanosheets (GNSs) have attracted significant scientific attention because of their remarkable features, including exceptional electron transport, excellent mechanical properties, high surface area, and antibacterial functions. Poly(vinyl alcohol) (PVA) solutions filled with GNSs were prepared for electrospinning, and their spinnability was correlated with their solution properties. The effects of GNS addition on solution rheology and conductivity were investigated. The as‐spun fibers were characterized via scanning electron microscopy (SEM), transmission electron microscopy (TEM), wide‐angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC). The results revealed the effects of GNS on the microstructure, morphology, and crystallization properties of PVA/GNS composite nanofibers. The addition of GNSs in PVA solution increased the viscosity and conductivity of the solution. The electrospun fiber diameter of the PVA/GNS composite nanofiber was smaller than that of neat PVA nanofiber. GNSs were not only embedded at the fibers but also formed protrusions on the fibers. In addition, the crystallinity of PVA/GNS fiber decreased with higher GNS content. The possible application of PVA/GNS fibers in tissue engineering was also evaluated. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41891.     

木质素在超临界甲醇和乙醇溶剂中液化过程分析

通过研究木质素分别在超临界甲醇和乙醇溶剂中的液化过程，分析反应温度（260～340℃）及反应时间（0～120min）对木质素在两种溶剂中的转化率、生物油收率及其组分差异的影响。实验表明，木质素在超临界乙醇中的转化率及产物收率均高于甲醇。当反应温度340℃，反应时间60min，木质素在超临界乙醇中的转化率和生物油收率比在甲醇中分别提高了16.23%和11.54%，残渣收率降低了16.23%。通过GC-MS和FTIR对生物油和残渣分析，发现生物油组分中芳香族化合物相对含量较高，在甲醇和乙醇溶剂中分别达到66.13%和58.84%；随着反应时间的延长，甲醇溶剂中残渣的醚键官能团逐渐增强，而在乙醇溶剂中则先增强后减弱。分析认为在木质素降解过程中，超临界乙醇和甲醇均可产生氢自由基作为供氢体，攻击木质素及其大分子片段中的官能团，同时使液化产物中的活性片段减活，减弱重聚合反应，从而更利于芳烃产物的生成。而甲醇在液化过程中容易与木质素断键产生的苯酚中间体发生脱氢缩合反应，通过醚键聚合产生长链芳香族化合物，形成残渣，降低生物油收率。     

Formation of Highly Aligned,Single‐Layered,Hollow Fibrous Assemblies and the Fabrication of Large Pieces of PLLA Membranes

Large pieces of paper‐thin PLLA membranes are prepared and characterized as single‐layered hollow fibrous assemblies with an extremely high degree of fiber alignment. The diameter of the electrospun hollow fibers is in the range of some tens of micrometers with a wall thickness of a few micrometers. They are best described as 2D arrays of highly aligned microtubes. The mechanical properties of the membranes are studied. A processing map is constructed using the applied electric field strength and the concentration (viscosity) of the electrospinning dope. The influence of factors such as the field strength and weight and viscosity of the jetted solutions is discussed. The results will help in the future fabrication of highly anisotropic scaffolds for tissue engineering applications.