Shear‐rate‐dependent rheology effects on mass transport and surface reactions in biomicrofluidic devices

Consideration is given to shear‐rate‐dependent rheology effects on mass transport in a heterogeneous microreactor of rectangular cross section, utilizing both numerical and analytical approaches. The carrier liquid obeys the power‐law viscosity model and is actuated primarily by an electrokinetic pumping mechanism. It is discovered that, considering the shear‐thinning biofluids to be Newtonian fluids gives rise to an overestimation of the saturation time. The degree of overestimation is higher in the presence of large Damkohler numbers and electric double layer thicknesses. It is also increased by the application of a favorable pressure gradient, whereas the opposite is true when an opposed pressure gradient is applied. In addition, a channel of square cross section corresponds to the maximum fluid rheology effects. Finally, the numerical results indicate the existence of a concentration wave when using long channels. This is confirmed by analytical solutions, providing a closed form solution for wave propagation speed. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1912–1924, 2015     

Analytical solutions for species transport in a T‐sensor at low peclet numbers

A 3D analytical solution is presented for the problem of mass transport in a T‐sensor by taking the axial diffusion effects into account. The solution methodology is based on an eigenfunction expansion of the solute concentration and enjoys the variational calculus for the solution of the associated eigenvalue problem. The method is capable of handling a mixed electroosmotic and pressure‐driven velocity profile and is executed assuming a rectangular channel cross‐section although it can be easily extended to more complex geometries. Two simplified models, one based on a uniform velocity profile, valid for the channel half height to Debye length ratios of above 100, and the other based on a depthwise averaging of the species concentration to be used for cases in which the channel width to height ratio is above 5 are also presented. As a part of the latter, expressions are derived for the Taylor dispersion coefficient of the mixed flow in a slit microconduit. The most interesting finding of this study is that, when the diffusion mechanism significantly contributes to the axial movement of the species, the well‐known heterogeneous mass transport evolves into a nearly uniform pattern in the depthwise direction and the mixing length noticeably increases. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4119–4130, 2016     

纳米技术与纳米碳管

叙述了纳米技术的特点，探讨了纳米碳管的研究和应用前景。     

A New Theoretical Approach To Electroosmotic Dewatering (Eod) Based On Non-Equilibrium Thermodynamics☆

ABSTRACT

A novel theoretical approach to electroosmotic dewatering (EOD), with or without a pressure gradient, of clays, sludges and other colloidal suspensions is proposed. The treatment is based on nan-equilibrium thermodynamics as developed in the work of Overbeek, De Groot and others. The interpretation of electrokinetic phenomena in terms of the cancepts of irreversible thermodynamics when combined with Onsager's relations, it has been shown by Overbeek, provides a complete framework for understanding all electrokinetic phenomena.

We have applied this approach here to the electroosmotic dewatering. both in the presence and absence of applied hydrostatic pressure.

The approach provides much clarification on the nature and significance of currents and fluxes observed during EOD: these are composed of three components, during combined pressure electroosmotic dewatering: (i) electrochemicavelectrical current; (ii) hydrodynamic flux: (iii) electroosmotic current.

We have also shown the manner in which the proposed new approach to EOD based on irreversible thermodynamics can be connected to the conventional approach based on the Helmholzu-Smoluchowski equation.     

Preparation of Magnetic Carbon Nanotubes (Mag-CNTs) for Biomedical and Biotechnological Applications

Carbon nanotubes (CNTs) have been widely studied for their potential applications in many fields from nanotechnology to biomedicine. The preparation of magnetic CNTs (Mag-CNTs) opens new avenues in nanobiotechnology and biomedical applications as a consequence of their multiple properties embedded within the same moiety. Several preparation techniques have been developed during the last few years to obtain magnetic CNTs: grafting or filling nanotubes with magnetic ferrofluids or attachment of magnetic nanoparticles to CNTs or their polymeric coating. These strategies allow the generation of novel versatile systems that can be employed in many biotechnological or biomedical fields. Here, we review and discuss the most recent papers dealing with the preparation of magnetic CNTs and their application in biomedical and biotechnological fields.     

多通道流动电泳的计算流体力学模拟与实验研究(Ⅰ)离子分布模型

多通道流动电泳（MFE）是一种制备型流动电泳技术,采用计算流体力学方法描述MFE设备中的流体流动特性,以指导分离过程和分离设备设计.基于MFE分离过程中离子迁移方程、电解质解离方程和电中性方程建立描述各腔室pH值及离子分布的模型,并通过实验进行了验证.为后续计算流体力学模拟各腔室流场分布提供了基础.     

Depletion of cross‐stream diffusion in the presence of viscoelasticity

An effort to analyze the viscoelasticity effects on transverse transport of neutral solutes between two miscible streams in an electrokinetic T‐sensor is presented. The analysis is based on an approximate analytical solution for the depthwise averaged concentration, assuming a channel of large width to depth ratio for which a one‐dimensional profile is sufficient for describing the velocity field. We show that the solution derived is surprisingly accurate even for very small channel aspect ratios and the maximum error reduces to only about 1% when the aspect ratio is 5. The developed model reveals that the mixing length for a viscoelastic fluid may be by far larger than that for a Newtonian fluid. Moreover, the Taylor dispersion coefficient for electroosmotic flow of viscoelastic fluids, which its determination is a main part of the analysis, is found to be an increasing function of both the elasticity level and the EDL thickness. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4533–4541, 2015     

Ion Transport in Sub-10 nm Nanofluidic Channels: Synthesis,Measurement, and Modeling

Recent advances in nanofabrication, measurement, and analysis techniques of nanofluidic systems have allowed ion transport to be systematically explored in narrow, confined channels with dimensions of less than about 10 nm. In such small dimensions, anomalous ion transport can be observed. This review describes several unique ion-transport phenomena recently reported in sub-10 nm fluidic channels and provides an introduction to recently developed nanofabrication techniques to create sub-10 nm nanochannels by both top-down and bottom-up approaches.     

柱内径对堆积边界法富集重现性的影响

Breadmore提出了一种新型毛细管电泳富集方法（电渗流控制下的逆流等速电泳堆积边界法富集）,可对阴离子实现十万倍在线富集效果。本文以NO3-为模型分子考察了不同内径毛细管柱对该富集重现性的影响。实验发现,使用内径为75μm的毛细管柱时富集重现性极不稳定,富集阶段电流对富集时间的积分面积和NO3-电泳峰面积的RSD（n=10）分别高达6.98%和105.43%,而使用内径为25μm的毛细管柱时富集重现性稳定,富集阶段电流对富集时间的积分面积和NO3-电泳峰面积的RSD（n=7）分别为0.96%和4.43%。实验结果表明这种富集方法的稳定性依赖于富集阶段电流对富集时间的积分面积的重现性,进而依赖于实验中采用的毛细管柱内径的大小尺寸。