The superhydrophobicity of polymer surfaces: Recent developments

Superhydrophobicity is the extreme water repellence of highly textured surfaces. The field of superhydrophobicity research has reached a stage where huge numbers of candidate treatments have been proposed and jumps have been made in theoretically describing them. There now seems to be a move to more practical concerns and to considering the demands of individual applications instead of more general cases. With these developments, polymeric surfaces with their huge variety of properties have come to the fore and are fast becoming the material of choice for designing, developing, and producing superhydrophobic surfaces. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1203–1217, 2011     

Heterogeneous Electrofreezing of Super-Cooled Water on Surfaces of Pyroelectric Crystals is Triggered by Trigonal Planar Ions

Electrofreezing experiments of super-cooled water (SCW) with different ions, performed directly on the charged hemihedral faces of pyroelectric LiTaO₃ and AgI crystals, in the presence and in the absence of pyroelectric charge are reported. It is demonstrated that bicarbonate (HCO₃⁻) ions elevate the icing temperature near the positively charged faces. In contrast, the hydronium (H₃O⁺) slightly reduces the icing temperature. Molecular dynamics simulations suggest that the hydrated trigonal planar HCO₃⁻ ions self-assemble with water molecules near the surface of the AgI crystal as clusters of slightly different configuration from those of the ice-like hexagons. These clusters, however, have a tendency to serve as embryonic nuclei for ice crystallization. Consequently, we predicted and experimentally confirmed that the trigonal planar ions of NO₃⁻ and guanidinium (Gdm⁺), at appropriate concentrations, elevate the icing temperature near the positive and negative charged surfaces, respectively. On the other hand, the Cl⁻ and SO₄²⁻ ions of different configurations reduce the icing temperature.     

应用极化水分子模型研究单分子层受限水的介电性质

受限条件下水的介电性质因测量极具挑战,其在诸多电化学过程与反应输运过程中如何扮演关键角色从未被定量地澄清.本工作利用平衡态分子动力学模拟和受限体系介电性质计算方法,系统性地探索了0.65 nm限域尺寸、5×10⁸ Pa限域压强、不同温度条件下单分子受限冰和受限水的介电性质.详细比较了恒定偶极矩SPC/E水分子模型和可极化的SWM4-NDP水分子模型在描述受限冰、水结构与介电性质上的优劣势,包括统计分析SWM4-NDP模型模拟的单分子层受限水和受限冰的瞬时分子偶极矩概率密度分布,计算每个模拟体系的静态结构因子、静态偶极空间关联函数、静态介电常数、体系偶极时间关联函数和德拜弛豫时间.首次发现了极化水分子模型描述的低维度受限水和受限冰的奇异分子极性变化,并观察到两种模型描述静态结构性质的效果相当,SWM4-NDP模型对于静态介电常数描述的优势会因受限条件的增强而被大幅削减.但在受限水介电极化弛豫动力学性质描述上SWM4-NDP模型明显优于SPC/E模型.我们推断SWM4-NDP模型在探索受限水结构相变动力学以及受限体系离子输运和溶剂化动力学等过程的模拟研究中是比SPC/E模型更好的选择.本工作将在进一步开展基于受限水系统储能、传感、输运的设计工作中提供一定的理论指导意义.     

限制在疏水板中的新的六边形-四边形三层冰结构

对限制在两个光滑的疏水板间的水进行了分子动力学模拟,观察到了两种晶体结构,都满足冰规则．在1GPa的压强和1．0nm的板间距下获得的新的冰相是平坦的六边形-四边形三层冰．在此结构中,靠近板的两层（外层）中的水分子形成六边形环,中间层的水分子形成四边形环．对于外层的水分子,其四个氢键中的三个在同一层中,另一个氢键与中间层连接．对于中间层的水分子,四个氢键中的两个在同。层中,而另外两个氢键与两个不同的外层相连．虽然三层的形状不同,但其面密度却接近相等．另一种结构是在0．8nm的板问距和100MPa的侧向压下获得的平坦的六边形双层冰．模拟中的相变既有一阶相变,也有连续相变．     

基于亮度均衡化的图像阈值分割技术在黄河冰凌监测中的应用

一种基于亮度均衡化的图像阈值分割算法被提出.该算法将冰凌图像亮度数据均衡化,以类间方差最大为标准,求得最佳阈值,并将冰凌图像转化为二值图像,通过冰凌像素统计,最终确定冰凌密度.该算法被应用于黄河河道冰凌图像密度的计算中,取得较好的效果.     

多面体截面和小覆盖的闭子流形

设π:M~n→P~n是P~n上的小覆盖,S是P~n的任意一个n-1维截面.给出了π~(-1)(S)是n-1维闭子流形(或者两个相互同胚n-1维闭子流形的不交并),以及π~(-1)(S)是n-1维伪流形的充要条件.     

Alliance free and alliance cover sets

A defensive (offensive) k-alliance in Γ = (V,E) is a set S ⊆ V such that every υ in S (in the boundary of S) has at least k more neighbors in S than it has in V / S. A set X ⊆ V is defensive (offensive) k-alliance free, if for all defensive (offensive) k-alliance S, S/X ≠ ∅, i.e., X does not contain any defensive (offensive) k-alliance as a subset. A set Y ⊆ V is a defensive (offensive) k-alliance cover, if for all defensive (offensive) k-alliance S, S ∩ Y ≠ ∅, i.e., Y contains at least one vertex from each defensive (offensive) k-alliance of Γ. In this paper we show several mathematical properties of defensive (offensive) k-alliance free sets and defensive (offensive) k-alliance cover sets, including tight bounds on their cardinality.     

人造柱状冰特性的研究

由于地形的变化,冰特性的研究对研究冰川、河、湖、海冰的动力过程以及破冰均有重要意义.本文对人造柱状冰的特性进行研究和分析,给出了人造柱状冰的制备过程和利用压力试验机对人造冰特性进行的测定,主要包括冰冻模具的制作、冰试样的制备和加工以及对于纯水冰柱和含沙冰柱的特性研究.在冰柱的冰冻温度为-10℃、-20℃、-30℃和-4...     

青藏高原雪冰样品中低含量水溶金属离子分析方法对比研究

从采自青藏高原阿汝和古里雅冰川的两支冰芯中选取31个样品,分别用三种仪器对比分析K^+、Na^+、Ca^2+、Mg^2+四种水溶金属离子,寻求最佳分析方案。分析结果对比发现,电感耦合等离子体发射光谱(ICP-OES)法在K+测量中存在困难,而离子色谱(IC)法和电感耦合等离子体质谱(ICP-MS)法均能够满足要求,且分析结果具有高度的一致性,四种离子的相关系数(R2)均在0.97以上,且并未出现ICP-MS法比IC法测量值明显偏高的现象。因此,除IC法外,ICP-MS法也是检测青藏高原雪冰样品中水溶金属离子的有效手段,其测定速度更快,且可以同时进行微、痕量元素检测,适用于大批量冰芯样品的快速分析。     

基于介质温度数值分布规律的冰盖厚度检测分析方法

针对水文预报领域冰层厚度检测过程中对空气与冰层、冰层与冰下水层的分界点难以判断的难题,提出了一种基于介质温度数值分布规律的冰层厚度检测分析方法.新方法在对空气与冰层、冰层与冰下水层的分界点进行分析判断时采用了聚类分析思想,通过采用改进属性归类规则的K-means算法,对采集到的空气、冰与水不同介质的温度数值分布数据进行分类,并对各自属性的温度梯度分布数据集合进行线性拟合,从各拟合曲线交点可以获得空气与冰层、冰层与冰下水层的分界点,进而计算出冰层厚度数值.采用这一方法对2014.12-2015.3内蒙包头黄河河道冰情采集数据进行分析,证明了新方法的可行性.