Tham khảo tài liệu 'the mems handbook mems applications (2nd ed) - m. gad el hak episode 2 part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Nonlinear Electrokinetic Devices 9-3 usually have turns to cover more areas. Taylor dispersion can result at the turns because of the difference in transit time or streamline velocity over the same length at the two sides of the turn. Taylor dispersion due to this transverse difference in velocity around turns can reduce the separation efficiency dramatically Dutta and Leighton 2001 . With low dispersion electrokinetic flow suffers from mixing deficiencies that reduce reaction yield and promote colloid protein aggregation precipitation Chang 2001 Thamida and Chang 2002 Takhistov et al. 2003 . Such undesirable colloidal segregation and aggregation phenomena in microdevices can be minimized if microvortices can be generated within the flow channels to mix the suspension. However generation of microvortices is difficult in electrokinetic flow due to its irro-tational features. One strategy is to introduce surfaces with nonuniform zeta potential Ajdari 1995 Herr et al. 2000 Stroock et al. 2002 . However such nonuniformities are difficult to impose at junctions and membrane surfaces where vortex mixing is most needed. Several micropumps based on linear electrokinetics have been reported in recent years Laser and Santiago 2004 Zeng et al. 2001 . Because of the large current of such linear electrokinetic pump bubble and ion generation by electrochemical reaction at the electrodes are major issues. A pH gradient often develops as a result of the ion production and will often produce nonuniform zeta potential due to its sensitivity to pH. Pressure-driven backflow and long circulations can then result due to such pH gradients Minerick et al. 2002 . Buffer solutions are usually used to neutralize the pH gradient but depending on the load and sample utilizing such buffer solutions is not always possible. A high voltage exceeding several hundred volts is usually required for linear electrokinetic pumps rendering them impractical or unsafe for portable devices. Dense packing .
