聚乙二醇的纳米二氧化硅分散系动态湿润特性

流体动态湿润在工业生产和高新技术的开发中有广泛应用,非牛顿流体动态湿润研究正处于起步阶段,并有着相对于牛顿流体更为实际的应用前景和价值。本文研究了一类具有复杂流变性的聚乙二醇的二氧化硅纳米颗粒分散体系的动态湿润特性。通过液滴铺展法得到了液滴半径随铺展时间的变化关系,以及动态接触角随接触线移动速度的变化关系的实验数据。实验结果表明,该类流体在云母表面上完全铺展,R～t关系符合Tanner定律,结合Starov的理论,分析R～t数据认为该类流体的中剪切速率阶段,即包含剪切增稠段的流变性对动态湿润有重要的影响。现有的动态接触角理论没有针对该类复杂流变流体的专用模型,研究发现分子运动理论模型不考虑黏性耗散,不仅适用于牛顿流体,对本文的θ_D～U数据同样能很好地描述,拟合参数符合物理意义。     

Electrical characteristics of Pt-ZnO Schottky nano-contact

The electrical characteristics of Pt-ZnO Schottky nano-contact have been studied. Well aligned ZnO nanorod arrays were synthesized by two-step wet-chemical method. A Pt-coated conducting probe of atomic force microscope was placed on the head face of the ZnO nanorod, thereby forming a Pt-ZnO nano-contact. The I-V characteristic curve shows that the Pt-ZnO nano-contact exhibits rectifying effect, like a Schottky diode with an ideality factor of 3.2 and a reverse-bias breakdown voltage more than -10 V. The st...     

Improvement in the blood compatibility of polyvinylidene fluoride membranes via in situ cross‐linking polymerization

In this study, we have provided a highly efficient, convenient, and universal protocol for preparing polyvinylidene fluoride (PVDF) membranes with low blood contact activation via in situ cross‐linking copolymerization of 2‐hydroxyethl methacrylate (HEMA) and acrylic acid (AA) in a solution of PVDF. The modified membranes were prepared from PVDF solution by phase inversion technology. The composition and morphology of the modified membranes were confirmed by attenuated total reflectance‐Fourier transform infrared (ATR‐FTIR) spectroscopy, thermogravimetric (TG) analysis, and scanning electron microscopy (SEM). Protein adsorption, clotting time, and contact activation on the modified PVDF membranes were systematically studied, the results indicating that after the incorporation of AA and HEMA, the modified PVDF membranes possessed anticoagulant properties in addition to low contact activation of blood components when in contact with blood. Therefore, fluorinated PVDF membranes with surfaces enriched with carboxyl and hydroxyl groups possessed the potential for use in long‐term blood‐contacting devices.     

A method to prepare gels with controllable morphology through a three‐phase system

Traditional methods for preparing hydrogels with specific morphology need molds with different shapes, which should bring about a complicated process. In order to control the size and morphology of hydrogels conveniently, a new simple synthesis method was advanced to prepare the gels. In this method, the prepolymer solution achieves diffusion in the interface between the upper oil phase and lower hydrogel matrix, which constitutes a three‐phase system, and the morphology of prepared gels was determined by the balanced diffusion status of the prepolymer solution. Hence, through controlling the composition and character of the three different phases in this system, the balanced diffusion status could be adjusted because of the changed interaction acting on the prepolymer solution diffused in the phase interface. The common rule with regards to the resulting morphology of prepared gels was investigated by surface tension analysis. The results prove that this synthetic method is feasible in preparing many kinds of hydrogels with controllable morphology as a common approach.     

二硫化钨/石墨烯异质结的界面相互作用及其肖特基调控的理论研究

采用第一性原理方法研究了二硫化钨/石墨烯异质结的界面结合作用以及电子性质,结果表明在二硫化钨/石墨烯异质结中,其界面相互作用是微弱的范德瓦耳斯力.能带计算结果显示异质结中二硫化钨和石墨烯各自的电子性质得到了保留,同时,由于石墨烯的结合作用,二硫化钨呈现出n型半导体.通过改变界面的层间距可以调控二硫化钼/石墨烯异质结的肖特基势垒类型,层间距增大,肖特基将从p型转变为n型接触.三维电荷密度差分图表明,负电荷聚集在二硫化钨附近,正电荷聚集在石墨烯附近,从而在界面处形成内建电场.肖特基势垒变化与界面电荷流动密切相关,平面平均电荷密度差分图显示,随着层间距逐渐增大,界面电荷转移越来越弱,且空间电荷聚集区位置向石墨烯层方向靠近,导致费米能级向上平移,证实了肖特基势垒随着层间距的增加由p型接触向n型转变.本文的研究结果将为二维范德瓦耳斯场效应管的设计与制作提供指导.     

New insights into the mechanism of wettability alteration during low salinity water flooding in carbonate rocks

There is not a consistent view about the mechanism of wettability alteration during low salinity water flooding. This paper highlights extensive wettability studies to investigate the wettability alteration on mineralogically different carbonates. Contact angle measurements were conducted to characterize wettability changes quantitatively. The results clearly revealed that wettability of carbonate rock surfaces can be altered to a more water-wet condition by lowering water salinity. The trend of the maximum change of contact angle (MCCA) variation with dolomite/calcite content in the rock is fairly linear under the same salinity, which demonstrates that carbonate minerals can affect rock wettability in a way. Also, the higher calcite content in the rock, the greater MCCA, i.e. the stronger effect of LSWF. Besides, the sensitivity of rock wettability to minerals is different under different salinity conditions. When the salinity is in the range of 2384.6?～?4769.2?mg/L, rock wettability is most sensitive to minerals. The analysis of the effect of ion composition showed that the effect of Ca²⁺ on wettability alteration is greater than that of Mg²⁺ at room temperature, and with the increase of the content of calcite in the rock, the effect of Ca²⁺ is more pronounced than that of Mg²⁺.     

First-principles study of metal-semiconductor contact between MX2 (M = Nb,Pt; X = S,Se) monolayers

First principles calculations are performed to investigate the structural and electronic properties of MX₂ (M = Nb, Pt; X = S, Se) monolayers and their van der Waals (vdW) heterostructures. The dynamical stability of monolayers and vdW heterostructures is confirmed by binding energy and phonon spectra. An indirect band gap nature is found for PtS₂ and PtSe₂ monolayers while NbS₂, NbSe₂ and all vdW heterostructures are metals. The intrinsic electronic properties of both NbX₂ and PtX₂ are well preserved due to weak vdW contact. It is demonstrated that a p-type Schottky contact with a small barrier height is formed at NbX₂-PtX₂ interface. The zero tunnel barrier and higher potential drop across the interface in these contacts imply large transfer of charge carriers across the interface, making them potential candidates in nanoelectronic device applications.     

铜铟镓硒薄膜太阳能电池新型图形化透明前电极研究

为了优化铜铟镓硒薄膜太阳能电池的前电极,提高铜铟镓硒薄膜太阳能电池的效率,提出了一种可应用于铜铟镓硒薄膜太阳能电池的AZO/图案化Ag薄膜/AZO结构的前电极,中间层的Ag薄膜与电池顶层的金属栅线具有完全相同的图案和尺寸,并且位于金属栅线的正下方,这种新型结构可以提高电池前电极的电学性能,但对电池来说不会带来额外的光学损失。对比了新型前电极结构与几种传统前电极的电学和光学性能,并且制备了相应的电池进行了性能对比。实验结果表明,新型的前电极结构可以提高铜铟镓硒薄膜太阳能电池的短路电流,相对传统AZO电极,电池效率从13. 83%提高到14. 53%。本结构可以明显提高电池效率。     

石墨烯与金属的欧姆接触理论研究

石墨烯材料应用于多种电子器件时不可避免地要与金属电极接触,它们之间的接触电阻直接影响了器件的性能.为了揭示影响金属电极与石墨烯间接触电阻的因素,提出有效地抑制这些影响的措施,本文建立了一种求解接触电阻的物理模型,将载流子的输运分为金属与正下方石墨烯之间、正下方石墨烯与邻近石墨烯之间的两个过程,分别研究各个过程的输运概率;结合金属电极与石墨烯接触对载流子分布的影响分析接触电阻,据此分别探讨了金属电极材料、栅极电压、掺杂浓度、金属与石墨烯原子距离等对接触电阻的影响.为验证理论分析结果的正确性,制作了金与石墨烯接触的实验样品,实验测得的接触电阻与理论分析结果符合.理论分析结果表明,可通过选择与石墨烯功函数接近的金属材料,降低二氧化硅层厚度,增加载流子平均自由程,改进金属材料的表面形态使其更光滑,减小金属与石墨烯耦合长度等方法降低石墨烯与金属电极的接触电阻.     

Investigation on nonlinear multi-scale effects of unsteady flow in hydraulic fractured horizontal shale gas wells

A unified mathematical model is established to simulate the nonlinear unsteady percolation of shale gas with the consideration of the nonlinear multi-scale effects such as slippage, diffusion, and desorption. The continuous inhomogeneous models of equivalent porosity and permeability are proposed for the whole shale gas reservoir including the hydraulic fracture, the micro-fracture, and the matrix regions. The corresponding semi-analytical method is developed by transforming the nonlinear partial differential governing equation into the integral equation and the numerical discretization. The non-linear multi-scale effects of slippage and diffusion and the pressure dependent effect of desorption on the shale gas production are investigated.