Mechano-nanofluidics: water transport through CNTs by mechanical actuation

Mechano-nanofluidics, defined as the study of mechanical actuation effects on the properties of nanofluidics, have received broad interest recently in the field of nanofluidics. The coupling between phonons in carbon nanostructures and fluids under confinement is verified to enhance the diffusion of fluids. Especially, carbon nanotubes (CNTs) are applied as perfect nanochannels with fast water mass transport, making them to be one of the next generation of membranes. Here, we investigated water permeation through CNT membranes with the mechanical vibrations using non-equilibrium molecular dynamics simulations. The simulation results reveal that the water flux is highly promoted by a travelling surface waves at 1 THz. The water flux is enhanced by as large as 20 times for the single-file structured water at 20 MPa. The vibration effect is verified to be equivalent to a pressure drop with \({{{\Delta}}}P\) up to 295 MPa. We show that the role of vibration diminishes for water in a larger CNTs. The water structure and hydrogen bond network are analyzed to understand the phenomena. The results of the present work are applied to provide guidance for the development of high-performance membranes.     

Dynamics of droplet transport induced by electrowetting actuation

This study reports on the dynamics of droplets in the capillary regime induced by electrowetting-on-dielectric actuation. The configuration investigated allows for comparing the experimental results with respect to the predictions of Brochard’s theoretical model (Brochard in Langmuir 5:432–438, 1989). Firstly, side-view observations using stroboscopic recording techniques were used to measure and analyse droplet deformations as well as the front and rear apparent contact angles during motion. Secondly, the influence of viscosity on the droplet velocity as a function of the applied voltage was studied. This has revealed that low Reynolds number droplet motion can be described by the simple laminar viscous model of Brochard. Finally, the influence of the dielectric thickness on the droplet dynamics was studied. It is shown that droplet velocity is limited by a saturation effect of the driving electrostatic force and that this phenomenon is very similar to that occurring in static experiments.     

Microfluidic liquid actuation through ground-directed electric discharge

In this article, we present a new technique to actuate liquids in microchannels using ground-directed electric discharge generated by a portable corona device. When an electric discharge is applied, the air in the microchannel is ionized causing a change in the surface energy. The resulting change in the contact angle induces rapid liquid transport through the channel by capillary action. In contrast to established plasma treatment this method employs a ground electrode that guides the electric field. This approach enables rapid treatment of select microchannels and thus provides a means of real-time fluid actuation as opposed to simply a pretreatment process. Instantaneous fluid velocities show power-law dependence with time and fit theoretical models at a contact angle of 65°. Average fluid velocities are on the order of 5 cm/s, and thus channels on the order of 1-cm long are filled in ~0.2 s. To demonstrate the potential of this technique for integrated lab-on-a-chip applications, the method was employed in serpentine channel, for on-demand fluid routing, to initiate a mixing process, and through an on-chip integrated microelectrode.     

Manipulation of ZnO nanostructures using dielectrophoretic effect

In this paper, the dielectrophoretic manipulation of the nanostructured zinc oxide (ZnO) with microfabricated electrodes and electrode arrays had been studied. The nanorod-like ZnO prepared by the chemical solution growth, with the length of 10 μm, was used as the manipulation target. The electrodes and electrode arrays were prepared by standard IC process. The SEM pictures have been used to examine and evaluate the manipulation results. The influences of the pattern of electrodes, the applied frequency, the concentration and the applied voltage on the dielectrophoretic manipulation effect have been investigated to research the manipulation of particles by dielectrophoresis. We succeeded in manipulating ZnO particles along the electric field and depositing them across the gaps between two electrodes by modulating different factors. It is concluded that the nanostructured ZnO can be manipulated by dielectrophoresis and both the positive dielectrophoretic effect and the negative dielectrophoretic effect can be observed. This manipulation technique is potential for lots of application such as the construction of micro/nano sensors and the nanoelectronic devices.     

Droplet creation using liquid dielectrophoresis

Dielectrophoresis (DEP) is defined as polarizable particles moving into regions of higher electric field intensity. In liquid DEP (LDEP), a dielectric liquid tends to flow toward regions of high electric field intensity under a non-uniform electric field. This work presents a theoretical model of LDEP based on parallel electrodes. The LDEP force is derived using the lump parameter electromechanical method. The relationship between the minimum actuation voltage and the electrode width is investigated experimentally and theoretically. We also propose a method for creating a 20 nl droplet of deionized water using LDEP. The creation of a water droplet containing 15 μm polystyrene beads is placed at the desired location from a continuous flow driven by LDEP using the developed method.     

Microfocusing using the thermal actuation of microbubbles

This paper describes the microfocusing in a microchannel using the thermal actuation of a pair of microbubbles. A microbubble was produced from de-ionized (DI) water with an integrated microheater, and the volume was controlled by applying voltage. The microfocusing was demonstrated with a polydimethylsiloxane (PDMS) device consisting of two layers. The top layer included a microchannel that was 300 μm wide and 50 μm high. It was flanked by a pair of reservoirs. The bottom layer provided a microheater underneath the reservoir. Upon heating, DI water boiled immediately over the microheater and formed a microbubble that came out of the reservoir in a perpendicular direction toward the fluid. The fluid was focused from 300 to 22 μm, as the distance between the apexes of the arch-shaped microbubbles was shortened due to expansion, which was maintained at a flow velocity up to approximately 17.8 mm s⁻¹. The temperature of the water in the reservoir was estimated to reach the boiling point within 62 or 160 ms, depending on the substrate.     

A PMMA valveless micropump using electromagnetic actuation

We have fabricated and characterized a polymethylmethacrylate (PMMA) valveless micropump. The pump consists of two diffuser elements and a polydimethylsiloxane (PDMS) membrane with an integrated composite magnet made of NdFeB magnetic powder. A large-stroke membrane deflection (~200 m) is obtained using external actuation by an electromagnet. We present a detailed analysis of the magnetic actuation force and the flow rate of the micropump. Water is pumped at flow rates of up to 400 µl/min and backpressures of up to 12 mbar. We study the frequency-dependent flow rate and determine a resonance frequency of 12 and 200 Hz for pumping of water and air, respectively. Our experiments show that the models for valveless micropumps of A. Olsson et al. (J Micromech Microeng 9:34, 1999) and L.S. Pan et al. (J Micromech Microeng 13:390, 2003) correctly predict the resonance frequency, although additional modeling of losses is necessary.     

Testing of MEMS capacitive accelerometer structure through electro-static actuation

The present paper discusses a method for testing a MEMS capacitive accelerometer structure through electrical actuation. The response of a standard MEMS capacitive accelerometer structure for different electrical actuation voltages has been analyzed. The accelerometer structure along with a capacitance sensing integrated circuit (IC) MS3110 is modeled and simulated. A set of proto-type accelerometer structures is fabricated and packaged in PGA packages. The packaged MEMS structures and MS3110 IC are integrated on a printed circuit board. The MEMS structure is actuated by applying the electrical signal through the actuation fingers and the change in capacitance is measured by the MS3110 IC. The simulated and measured results show some interesting phenomenon like dipping and frequency doubling which are useful for initial testing and characterization of a MEMS accelerometer structure.     

Transport of drug particles in micropumps through novel actuation

Micropumps with various types of actuations have been used in lab-on-a-chip devices. In order to control the delivery of drug particles both in space and time and avoid clogging, other types of actuation mechanisms may be needed. In this study, a valveless micropump with novel actuation is proposed to transport particles for biomedical and environmental applications. The transport of drug particles through the designed valveless micropump is carried out through computational fluid dynamics combined with discrete particle transport methods. After convergence studies, the effects of actuation frequency, particle size and the resident times on the particle transport are investigated. Interestingly, both the actuation frequency and particle size have a strong effect in terms of resident times and the spatial distribution of the transported particles through the designed micropump. Based on the results obtained, the relationship between actuation frequency, fluid flow, and particle transport through the designed micropump is presented. The computational analysis presented demonstrates that it is possible to optimize the proposed valveless micropump design for specific delivery of drug particles for separation and sorting applications.     

Droplet transport by electrowetting: lets get rough!

Since the pioneering works of Wenzel and Cassie Baxter in the 1930s, and now with the trivialization of the micro- and nanotechnology facilities, superhydrophobic surfaces have been announced as potentially amazing components for applications such as fluidic, optical, electronic, or thermal devices. In this paper, we show that using superhydrophobic surfaces in digital microfluidic devices could solve some usual limitations or enhance their performances. Thus, we investigate a specific monophasic (air environment) microfluidic device based on electrowetting integrating either a hydrophobic or a superhydrophobic surface as a counter-electrode. The droplet transport using a superhydrophobic surface compared with a classical hydrophobic system led to some original results. Characterization of the dynamic contact angle and the droplet shape allows us to get new insight of the fluid dynamics. Among the remarkable properties reported, a 30 % lower applied voltage, a 30 % higher average speed with a maximum instantaneous speed of 460 mm/s have been measured. Furthermore, we have noticed a huge droplet deformation leading to an increase by a factor 5 of the Weber number (from 1.4 to 7.0) on SH compared to hydrophobic surfaces. Finally, we discuss some of the repercussions of this behaviour especially for microfluidic device.     

A microgripper using piezoelectric actuation for micro-object manipulation

Design, fabrication and tests of a monolithic compliant-flexure-based microgripper were performed. The geometry design and the material stresses were considered through the finite element analysis. The simulation model was used to study in detail profiles of von Mises stresses and deformation. The maximum stress in the microgripper is much smaller than the critical stress values for fatigue. The microgripper prototype was manufactured using micro-wire electrode discharge machining. A displacement amplification of 3.0 and a maximum stroke of 170 μm were achieved. The use of piezoelectric actuation allowed fine positioning. Micromanipulation tests were conducted to confirm potential applications of the microgripper with piezoelectric actuation in handling micro-objects. The simulation and experimental results have proven the good performance of the microgripper.     

Droplet dynamics passing through obstructions in confined microchannel flow

Motivated by the previous studies (Lee et al., Lab Chip 10:1160–1166, 2010; Link et al., Phys Rev Lett 92:054503-1–054503-4, 2004), the droplet dynamics passing through obstructions in confined microchannel was explored both numerically and experimentally. The effects of obstruction shape (cylinder and square), droplet size, and capillary number (Ca) on droplet dynamics were investigated. For the size control, due to an obstruction-induced droplet breakup, the cylinder obstruction was found to be advantageous over square type for practical purposes. The thread breakup was attributed to both normal and shear components of velocity gradients near the obstruction, in particular, near the corners of the square. As a result, the square obstruction was considered to generate more non-trivial satellite droplets. The droplet size showed little influence on the droplet dynamics. Considering the wetting process on the cylinder surface, we explored the droplet dynamics passing through two successive cylinder obstructions, where more complicated dynamics was observed depending on Ca (capillary number ~ viscous force / interface tension), cylinder interval, and droplet size. Here, we propose two requirements for independent wetting on each cylinder: (i) low Ca droplet should be manipulated, and (ii) cylinder interval should be larger than channel width. That is, low Ca droplet could intrude the region between two cylinders if the cylinder interval was far enough, while the droplet could not intrude due to geometric hindrance for close obstructions. In the numerical viewpoint, the proposed requirements were also valid for multi-cylinder obstructions up to 6. In addition, we propose a novel design of array structure of cylinders for a selective wetting, which might be useful to fabricate Janus particles. We hereby prove by both simulation and experiments that the wetting on the obstruction is controllable by changing Ca and cylinder design in the multilayer deposition process.     

Thermocapillary actuation of liquid plugs using a heater array

With the aim toward realizing polymerase chain reaction (PCR) of deoxyribonucleic acid (DNA) in plug-based capillary platforms, this paper reports the theoretical and experimental results of thermocapillary actuation for temperature cycling with an arbitrary ramping function. Two concepts were investigated: (a) actuation and spatial temperature cycling with three heaters and (b) actuation and temporal cycling with two heaters. The paper first describes the analytical models of both concepts. The model considers the spatio-temporal heat transfer effects, which is coupled with the surface tension driven movement of the plug. In the experiments, both temperature field and plug motion were measured and evaluated. The temperature field was captured by an infrared thermal tracer camera. The position of the plugs was automatically captured and evaluated with a CCD camera. Finally, analytical and experimental results are compared and discussed.     

Numerical and experimental characterization of 3-phase rectification of nanobead dielectrophoretic transport exploiting Brownian motion

We report on a transport system for nanobeads that exploits Brownian motion as the main actuation source, saving energy compared to a purely electrostatic transport system of the same geometry. The transport system employs a microfluidic channel to restrict Brownian motion of the nanobeads to only one dimension and a 3-phase dielectrophoretic flashing ratchet to bias the spatial probability distribution into the rectification direction for one-dimensional transport. A numerical model of the system is developed and applied to investigate its performance. A micromachined transport system is fabricated and employed to experimentally validate the model with the confirmation of the optimal operation point. Numerical model and experiments have shown good agreement.     

Continuous size-based focusing and bifurcating microparticle streams using a negative dielectrophoretic system

Dielectrophoresis (DEP) is an electrokinetic phenomenon which is used for manipulating micro- and nanoparticles in micron-sized devices with high sensitivity. In recent years, electrode-based DEP by patterning narrow oblique electrodes in microchannels has been used for particle manipulation. In this theoretic study, a microchannel with triangular electrodes is presented and a detailed comparison with oblique electrodes is made. For each shape, the behavior of particles is compared for three different configurations of applied voltages. Electric field, resultant DEP force, and particle trajectories for configurations are computed by means of Rayan native code. The separation efficiency of the two systems is assessed and compared afterward. The results demonstrate higher lateral DEP force, responsible for particle separation, distributed wider across the channel width for triangular shape electrodes in comparison with the oblique ones. The proposed electrode shape also shows the ability of particle separation by attracting negative DEP particles to or propelling them from the flow centerline, according to the configuration of applied voltages. A major deficiency of the oblique electrodes, which is the streamwise variation of the lateral DEP force direction near the electrodes, is also eliminated in the proposed electrode shape. In addition, with a proper voltages configuration, the triangular electrodes require lower voltages for particle focusing in comparison with the oblique ones.     

Design and numerical analysis of interdigitated radiating-strips electrode for uniform 3D dielectrophoretic patterning of liver cells

Microsystem Technologies - This paper presents the design and numerical analysis of a new three-dimensional (3D) electrode having a non-uniform electric field gradient for dielectrophoretic...     

Active carbody roll control in railway vehicles using hydraulic actuation

Carbody tilting is used in railway vehicles to reduce the exposure of passengers to lateral acceleration in curves, allowing these to be negotiated at higher speeds with the same level of comfort. This, however, requires a rather complex actuation system that increases vehicle weight and reduces space for passengers.This paper introduces a new concept that provides a limited amount of carbody tilt using hydraulic actuation. The device consists of interconnected hydraulic actuators attached to the carbody and bogies, replacing the passive anti-roll bar used in railway vehicles and in addition permitting active tilt control.Three control strategies for the active hydraulic suspension are proposed, and the regulator gains are defined using Genetic Algorithm optimisation, based on numerical simulation of the running behaviour of the actuated railway vehicle in a high-speed curve. Finally, the performance of the actuated vehicle is assessed on the basis of numerical simulations, showing it is possible to increase significantly the vehicle׳s running speed in fast curves compared with a vehicle equipped with passive suspension.     

RF-MEMS switch actuation pulse optimization using Taguchi��s method

Reliability and longevity comprise two of the most important concerns when designing micro-electro-mechanical-systems (MEMS) switches. Forcing the switch to perform close to its operating limits underlies a trade-off between response bandwidth and fatigue life due to the impact force of the cantilever touching its corresponding contact point. This paper presents for first time an actuation pulse optimization technique based on Taguchi’s optimization method to optimize the shape of the actuation pulse of an ohmic RF-MEMS switch in order to achieve better control and switching conditions. Simulation results show significant reduction in impact velocity (which results in less than 5 times impact force than nominal step pulse conditions) and settling time maintaining good switching speed for the pull down phase and almost elimination of the high bouncing phenomena during the release phase of the switch.     

Spatial-mode analysis of micromachined optical cavities using electrothermal mirror actuation

The performance of optical microcavities is limited by spectral degradation resulting from thermal deformation and fabrication imperfections. In this paper, we study the spatial-mode properties of micromirror optical cavities with respect to commonly seen aberrations. Electrothermal actuation is used to slightly adjust the shape and position of micromirrors and study the effects this has on the spatial-mode structure of the cavity spectrum. The shapes of the micromirrors are changed using Joule heating with thermal expansion deformation. Significant differences in mirror tilt, curvature, and astigmatism are measured, but the tilt has by far the biggest impact on cavity finesse and resolution. We demonstrate that unwanted higher order spatial modes can be suppressed electrically and an amplitude reduction for the higher order modes of over 60% has been obtained with a tuning current of 5.5 mA. A fundamental mode finesse of approximately 60 is maintained throughout tuning. These tunable cavities have great potential in applications using cavity arrays or requiring dynamic mode control.     

Droplet mixing using electrically tunable superhydrophobic nanostructured surfaces

We demonstrate effective mixing of microliter droplets using electrically tunable superhydrophobic nanostructured surfaces. By applying electrical voltage and current, droplets can be reversibly switched from a wetting to a non-wetting state, which induces fluid motion within the droplet. This mixing concept was verified using a DNA hybridization assay, in which a single droplet reversibility accelerated the hybridization reaction by an order of magnitude as compared to mixing by passive diffusion. This work offers a new method to effectively mix droplets for a variety of microfluidics applications.