Optimal control-based inverse determination of electrode distribution for electroosmotic micromixer

This paper presents an optimal control-based inverse method used to determine the distribution of the electrodes for the electroosmotic micromixers with external driven flow from the inlet. Based on the optimal control method, one Dirichlet boundary control problem is constructed to inversely find the optimal distribution of the electrodes on the sidewalls of electroosmotic micromixers and achieve the acceptable mixing performance. After solving the boundary control problem, the step-shaped distribution of the external electric potential imposed on the sidewalls can be obtained and the distribution of electrodes can be inversely determined according to the obtained external electric potential. Numerical results are also provided to demonstrate the effectivity of the proposed method

Numerical characterization of silicon DC electro-osmotic pumps: the role of the micro channel geometry

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.A numerical analysis of silicon DC open channel EOPs is presented to show which parameters should be taken into account in the design of these devices. Particular attention is paid to the influence of the channel cross-section geometry on pump behavior, especially in relation to the electrical properties of the fluid. Rectangular and trapezoidal, micro and nano channels chemically etched on silicon wafers are considered and a broad range of operative conditions are analyzed. In order to make all the results available, two user-friendly correlations that predict the characteristic curves of the pumps are given as functions of the relevant parameters. The EOP model used to obtain the results is explained extensively, as well as the method used to solve it. A brief discussion on the domain in which it applies is also presented

The development of a method to determine felinine in body fluids by capillary electrophoresis : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy in Chemistry at Massey University

Ion-exchange, paper-chromatography and high performance liquid chromatography were used in earlier studies for the determination of felinine in biological fluids. These methods were either inadequate and/or need laborious sample pre-treatments. A new method for the determination of felinine by capillary zone electrophoresis has been developed. Preliminary investigations were carried out to address the conditions required for the separation of felinine. The separation of felinine can be performed on a fused-silica capillary with a 20 mM phosphate buffer (pH 2.0) and detection wavelength 200 nm. The separation principle was based on the different migration times due to the different molecular weights, molecular sizes and charges under an applied potential field. The quantitative determination of felinine levels in cat urine has been achieved. The cat urine analysis was performed directly on the capillary electrophoresis without making any felinine derivative(s). The levels of felinine in different cat genders are reported. The results were compared with the results of an HPLC felinine derivatization method. Felinine levels in entire male cat urine were much higher than those in female and castrated male cat urine. A synthetic felinine was employed as standard felinine. Linear relationships between peak area and concentration of synthetic felinine calibrations are reported. Mean felinine recovery in cat urine was 95.9%. Taurine, urea, creatine and creatinine, which exist in large amounts in cat urine, showed no interference with the analysis of felinine by this method. The new capillary zone electrophoresis method was then applied to the study of felinine stability. Conditions reported to influence the stability of felinine were investigated. These conditions included oxidation, storage temperatures and times, heating, acidic and alkaline solutions. Both synthetic felinine and felinine in cat urine were investigated. Storage temperature (-20°C to 20°C) had no significant influence on the stability of felinine while higher temperatures increased the decomposition of felinine. Felinine degraded at strong acid and base conditions but was relatively stable under mild acid and base conditions. A similar stability of felinine in human urine is also reported. The capillary zone electrophoresis method was also employed to study felinine in plasma and serum. Plasma and serum as well as urine can be analysed directly on the capillary electrophoresis after sufficient dilution. Conditions (eg. protein clean up, changing of injection time, 37°C heating) that might influence of felinine behaviour in plasma and serum are discussed. This study indicated that no traces felinine be found in cat plasma, within the detection limits of this new capillary electrophoresis method

Numerical Simulation of Electroosmotic Flow with Step Change in Zeta Potential

Electroosmotic flow is a convenient mechanism for transporting polar fluid in a microfluidic device. The flow is generated through the application of an external electric field that acts on the free charges that exists in a thin Debye layer at the channel walls. The charge on the wall is due to the chemistry of the solid-fluid interface, and it can vary along the channel, e.g. due to modification of the wall. This investigation focuses on the simulation of the electroosmotic flow (EOF) profile in a cylindrical microchannel with step change in zeta potential. The modified Navier-Stoke equation governing the velocity field and a non-linear two-dimensional Poisson-Boltzmann equation governing the electrical double-layer (EDL) field distribution are solved numerically using finite control-volume method. Continuities of flow rate and electric current are enforced resulting in a non-uniform electrical field and pressure gradient distribution along the channel. The resulting parabolic velocity distribution at the junction of the step change in zeta potential, which is more typical of a pressure-driven velocity flow profile, is obtained.Singapore-MIT Alliance (SMA

Enhancement of charged macromolecule capture by nanopores in a salt gradient

Nanopores spanning synthetic membranes have been used as key components in proof-of-principle nanofluidic applications, particularly those involving manipulation of biomolecules or sequencing of DNA. The only practical way of manipulating charged macromolecules near nanopores is through a voltage difference applied across the nanopore-spanning membrane. However, recent experiments have shown that salt concentration gradients applied across nanopores can also dramatically enhance charged particle capture from a low concentration reservoir of charged molecules at one end of the nanopore. This puzzling effect has hitherto eluded a physically consistent theoretical explanation. Here, we propose an electrokinetic mechanism of this enhanced capture that relies on the electrostatic potential near the pore mouth. For long pores with diameter much greater than the local screening length, we obtain accurate analytic expressions showing how salt gradients control the local conductivity which can lead to increased local electrostatic potentials and charged analyte capture rates. We also find that the attractive electrostatic potential may be balanced by an outward, repulsive electroosmotic flow (EOF) that can in certain cases conspire with the salt gradient to further enhance the analyte capture rate.Comment: 10 pages, 6 Figure