Diffusion of a chemically active colloidal particle in composite channels

Diffusion of colloidal particles in microchannels has been extensively investigated, where the channel wall is either a no-slip or a slip-passive boundary. However, in the context of active fluids, driving boundary walls are ubiquitous and are expected to have a substantial effect on the particle dynamics. By mesoscale simulations, we study the diffusion of a chemically active colloidal particle in composite channels, which are constructed by alternately arranging the no-slip and diffusio-osmotic boundary walls. In this case, the chemical reaction catalyzed by the active colloidal particle creates a local chemical gradient along the channel wall, which drives a diffusio-osmotic flow parallel to the wall. We show that the diffusio-osmotic flow can significantly change the spatial distribution and diffusion dynamics of the colloidal particle in the composite channels. By modulating the surface properties of the channel wall, we can achieve different patterns of colloidal position distribution. The findings thus propose a novel possibility to manipulate colloidal diffusion in microfluidics, and highlight the importance of driving boundary walls in dynamics of colloidal particles in microchannels.     

层流圆管潜射流生成蘑菇形涡结构特性数值研究

基于不可压Navier-Stokes方程, 采用计算流体力学方法, 数值模拟与分析了层流圆管潜射流在密度均匀黏性流体中的演化机理及其表现特征, 定量研究了蘑菇形涡结构无量纲射流长度L^*、螺旋型涡环半径R^*及其包络外形长度d^*等几 何特征参数随无量纲时间t^*的变化规律. 数值结果表明, 蘑菇形涡结构的形成与演化过程可分为三个不同的阶段: 启动阶段、发展阶段和衰退阶段. 在启动阶段, L^*和d^*随t^* 线性变化, 而R^*则近似为一个常数; 在发展阶段, 蘑菇形涡结构的演化具有自相似性, L^*, R^*和d^*与t^*1/2均为同一正比关系, 而且雷诺数和无量纲射流时间不影响该正比关系; 在衰退阶段, L^* 和R^* 正比于t^*1/5, 而d^*则近似为一个常数. 此外, 还对蘑菇形涡结构二次回流点、 动量源作用中心及其几何中心的速度变化规律、垂向涡量分布特征和 涡量-流函数关系进行了分析. 关键词： 圆管潜射流 蘑菇形涡结构 演化机理     

Multi-relaxation time lattice Boltzmann simulation of inertial secondary flow in a curved microchannel

The inertial secondary flow is particularly important for hydrodynamic focusing and particle manipulation in biomedical research.In this paper,the development of the inertial secondary flow structure in a curved microchannel was investigated by the multi relaxation time lattice Boltzmann equation model with a force term.The numerical results indicate that the viscous and inertial competition dominates the development of secondary flow structure development.The Reynolds number,Dean number,and the cross section aspect ratio influence significantly on the development of the secondary vortexes.Both the intensity of secondary flow and the distance between the normalized vortex centers are functions of Dean numbers but independent of channel curvature radius.In addition,the competition mechanism between the viscous and inertial effects were discussed by performing the particle focusing experiments.The present investigation provides an improved understanding of the development of inertial secondary flows in curved microchannels.     

土槿皮新二萜成分的研究 Ⅲ.土槿甲酸苷和土槿乙酸苷的分离及结构测定

前报报道了土槿皮(Pseudolarix kaempferi,Gord.)中抗真菌有效成分新二萜酸——土槿甲、乙、丙和丙_2酸的结构研究。现自土槿皮中继续分离得苷1和苷2,经化学和物理方法证明1为土槿甲酸-β-D-葡萄糖苷,2为土槿乙酸-β-D-葡萄糖苷。 1为白色粉末状固体,难溶于乙醚等低极性溶剂中,亦难溶于水和碳酸氢钠水溶液中,易溶于乙酸乙酯和醇中。IR示有羟基、酯基及双键,但无羧基吸收峰。~1H NMR与土槿甲酸的相似,但明显出现了糖的质子信号。糖端基质子信号δ5.66(d,J=7.5Hz),其位移值比糖接在醇羟基上的低。结合IR测知无羧基及在碳酸氢钠水溶液中不溶解,推测糖接在羧基上。质     

自扩散泳微观转动马达的介观模拟

转动的微尺度马达是一类重要的微流器件.近年来,因为其重要的应用及理论价值引起了学术界的广泛关注.本文提出了一种新型的自扩散泳驱动的微观转动马达模型.通过介观动力学模拟,验证了该模型的有效性.模拟结果表明,该自扩散泳微观转动马达可以单向地自驱动转动,并且转动速度和马达表面发生的催化化学反应速率(即自产生的浓度梯度场强弱)、以及液体分子与马达之间的相互作用有关.此外,研究了两个转动马达共存时的运动行为,重点考察了马达之间的流体力学相互作用和浓度梯度场效应对马达转动的影响.该自扩散泳微观转动马达为设计实用的微流器件提供了新的思路和参考,也为研究活性胶体系统的集体行为提供了理想模型.     

Experimental and numerical study on energy dissipation in freely cooling granular gases under microgravity

Energy dissipation is one of the most important properties of granular gas, which makes its behavior different from that of molecular gas. In this work we report our investigations on the freely-cooling evolution of granular gas under microgravity in a drop tower experiment, and also conduct the molecular dynamics(MD) simulation for comparison.While our experimental and simulation results support Haff's law that the kinetic energy dissipates with time t as E(t) ～(1 + t/τ)~(-2), we modify τ by taking into account the friction dissipation during collisions, and study the effects of number density and particle size on the collision frequency. From the standard deviation of the measured velocity distributions we also verify the energy dissipation law, which is in agreement with Haff's kinetic energy dissipation.     

格子玻尔兹曼方法模拟弯流道中粒子的惯性迁移行为

本文发展了一个能够模拟微流场环境下粒子惯性迁移行为的三维耦合模型.该模型采用基于动理论的格子玻尔兹曼方法(LBM)描述流体流动,采用牛顿动力学模型描述粒子的平动和转动,采用基于LBM反弹格式的运动边界法实现流体与粒子模型的耦合.模拟了重力作用下粒子的沉降过程和Couette流条件下粒子的转动过程,通过将模拟结果与文献中的基准解进行对比定量验证了模型的可靠性.模拟了不同大小的球形粒子在环形流道中的迁移,成功复现了经典的流道截面二次流形成过程,分析了粒径大小对粒子在流道中平衡位置的影响机理.结果表明,粒子在弯流道中的平衡位置与粒径大小密切相关,小半径粒子的平衡位置靠近流道外侧而大半径粒子则靠近流道内侧.通过实验对模拟结果进行了定性验证.本模型为深入研究微流场环境下粒子的运动特性以及开发微流控粒子分选器件提供了参考依据.     

胶体在非晶研究中的应用

胶体玻璃作为一种软物质材料由于其独特的物理化学特性在非晶态物理的研究中有重要的应用.本文简要介绍了胶体玻璃与玻璃材料的联系,并通过具体的研究实例介绍了胶体玻璃在研究非晶结构、动力学以及热力学方面的应用,对胶体玻璃未来的研究进行了展望.     

高中新课标数学必修①与必修④教学体会

从2004年9月开始,部分省区率先进行普通高中课程标准的实验教学,而湖北省也从2009年9月开始使用人教A版《普通高中课程标准实验教科书》．作为湖北省参与普通高中课程标准第一批实验的老师,我想结合人教A版《普通高中课程标准实验教科书·数学1（必修）》（以下简称《必修1》）及《必修4》两册教材的教学情况,谈谈高一年级第一学期数学新课标教学中的一些体会．     

钙钛矿薄膜气相制备的晶粒尺寸优化及高效光伏转换

钙钛矿薄膜的气相制备是一种极具潜力的工业化生产工艺,但薄膜的质量控制目前远落后于溶液制备法.本文通过建立PbI_2薄膜向钙钛矿薄膜完全转化过程中反应时间、晶粒尺寸与温度的关系,实现了薄膜的质量优化及大面积钙钛矿薄膜的制备,将薄膜的平均晶粒粒径从0.42μm优化到0.81μm.基于空间电荷限制电流模型对缺陷密度的研究显示,钙钛矿薄膜的缺陷密度由5.90×10~(16)cm~(–3)降低到2.66×10~(16)cm~(–3).光伏器件(FTO/TiO_2/C_(60)/MAPbI_3/spiro-OMeTAD/Au结构)测试显示,面积为0.045cm~2器件的平均光电转换效率从14.00%提升到17.42%,最佳光电转换效率达到17.80%,迟滞因子减小至4.04%.同时,基于180℃制备的1cm~2器件的光电转换效率达到13.17%.