Electrical Textile Valves for Paper Microfluidics

This paper describes electrically-activated fluidic valves that operate based on electrowetting through textiles. The valves are fabricated from electrically conductive, insulated, hydrophobic textiles, but the concept can be extended to other porous materials. When the valve is closed, the liquid cannot pass through the hydrophobic textile. Upon application of a potential (in the range of 100–1000 V) between the textile and the liquid, the valve opens and the liquid penetrates the textile. These valves actuate in less than 1 s, require low energy (≈27 µJ per actuation), and work with a variety of aqueous solutions, including those with low surface tension and those containing bioanalytes. They are bistable in function, and are, in a sense, the electrofluidic analog of thyristors. They can be integrated into paper microfluidic devices to make circuits that are capable of controlling liquid, including autonomous fluidic timers and fluidic logic.Chemistry and Chemical Biolog

Microfluidics: Fluid physics at the nanoliter scale

Microfabricated integrated circuits revolutionized computation by vastly reducing the space, labor, and time required for calculations. Microfluidic systems hold similar promise for the large-scale automation of chemistry and biology, suggesting the possibility of numerous experiments performed rapidly and in parallel, while consuming little reagent. While it is too early to tell whether such a vision will be realized, significant progress has been achieved, and various applications of significant scientific and practical interest have been developed. Here a review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena. Specifically, this review explores the Reynolds number Re, addressing inertial effects; the Péclet number Pe, which concerns convective and diffusive transport; the capillary number Ca expressing the importance of interfacial tension; the Deborah, Weissenberg, and elasticity numbers De, Wi, and El, describing elastic effects due to deformable microstructural elements like polymers; the Grashof and Rayleigh numbers Gr and Ra, describing density-driven flows; and the Knudsen number, describing the importance of noncontinuum molecular effects. Furthermore, the long-range nature of viscous flows and the small device dimensions inherent in microfluidics mean that the influence of boundaries is typically significant. A variety of strategies have been developed to manipulate fluids by exploiting boundary effects; among these are electrokinetic effects, acoustic streaming, and fluid-structure interactions. The goal is to describe the physics behind the rich variety of fluid phenomena occurring on the nanoliter scale using simple scaling arguments, with the hopes of developing an intuitive sense for this occasionally counterintuitive world

New driving schemes of cholesteric liquid crystal display for high speed and uniform gray-scale performance

Cholesteric LCD (Ch-LCD) is a special kind of electronic paper display. For quite a long time, lacking of fast and effective driving schemes is a primary limitation for the enhancement of its performance. In this thesis an improved dynamic driving scheme (DDS) with the ability of driving the Ch-LCD not only into the on-off state but also into several distinct gray scales has been proposed through newly designed waveform patterns. Besides, new driving scheme called as multi-selection method (MSM) is proposed for the first time to enlarge the gray scale number. In order to further enhance the gray scale’s uniformity, a fast static driving scheme with about 2ms/line is also proposed. Multiline driving scheme for Ch-LCD has been achieved and incorporated in the enhanced DDS. All of the driving schemes have been validated by using a newly designed discrete driver system including a Vertex 5 FPGA for pattern generation. Results are quite good and consistent with the expectations.Für eine lange Zeit war das Fehlen eines effektiven Treiberschemas ein Haupthindernis für die Anwendung der Cholesterischen LCDs. Als Verbesserung führen wir ein verbessertes dynamisches Treiberschemata (genannt Enhanced Dynamic Driving Scheme) ein, das ermöglicht, das Ch-LCD nicht nur in den Ein- oder Aus-Zustand, sondern auch in mehrere verschiedene Graustufen anzusteuern. Um die Anzahl der Graustufen durch das Enhanced DDS zu erhöhen, haben wir eine neue Multi-Selection-Method (MSM), vorgeschlagen. Um die Gleichmäßigkeit der Graustufen in einer hohen Ansteuergeschwindigkeit zu verbessern, schlagen wir ein Fast Static Driving Scheme, vor, das auf dem Übergang von einem stabilen Zustand in einen anderen stabilen Zustand, aber nicht über einen meta-stabilen Zustand, basiert ist. Ein weiteres Verfahren ist das Multiline Addressing Verfahren, für das Enhanced DDS entworfen, um die vier Kombinationen der angesteuerten Zuständen zu erzielen. Um die Treiberschemata in dieser Arbeit zu validieren, wurden vier diskrete Treiber-Platinen entworfen und hergestellt

Voltage induced spreading and liquid optical devices

An experimental investigation has been carried out into Liquid dielectrophoresis (LDEP), in which dielectric forces are used to actuate bulk liquid spreading and to imprint a deformation pattern at a liquid air surface. Our basic conguration uses a set of co-planar stripe interdigital electrodes to create a non-uniform A.C. electric field that exponentially decays in amplitude and penetrates above the structure into a dielectric liquid droplet. Dielectric forces drive a voltage-induced spreading of the droplet into a low contact angle droplet/film, an effect which will be referred to here as "dielectrowetting". Further application of the A.C. voltage to the electrodes results in a static sinusoidal wrinkle forming at the oil-air interface on the spread film. Three main areas of investigations are reported, the first of which is a study of the statics and dynamics of the voltage induced spreading of a stripe of the material 1,2 propylene glycol. In the limit of thick droplets, a theoretical prediction has been derived that the cosine of the static equilibrium contact angle is proportional to the square of the amplitude of the voltage applied to the inter-digital electrodes. This relationship is analogous to that found for electrowetting-on-dielectric (EWOD). Experimental observations confirm this predicted dielectrowetting behavior for the advancing static contact angle of the voltage induced spreading of a stripe of the material 1,2 propylene glycol

Investigation of flexoelectricity and ionic contamination in nematic liquid crystals

The work presented is a study of nematic liquid crystal physical properties. One of the phenomenon investigated is the bistability or in other words, the ability of the director of the material to rest in different orientations as function of the geometry of the sidewall. The main core of this research is the study of exoelectric effect and ionic contamination within the nematic layer. This can be split into three approaches. In the first part, the exoelectric coefficients are determined from the distortion of a nematic liquid crystal in response to non uniform electric fields created using an interdigitated electrode architecture. The distortion was deduced from the fringes movement in a Mach-Zhender interferometer built especially for this investigation. In the second part, the transient capacitance technique is used to measure the permittivity response of two homogeneous nematic materials subjected to different electric signal waveforms. The results remain to be fitted in order to give an alternative method to deduce the exoelectric coefficients values and a better understanding of the effect of ionic contamination. The last part of the work relates to the determination of the exoelectricity coefficients and ionic contamination and their effects on the Fréedericksz transition in homogeneous nematic liquid crystal using magnetic fields. The Mach-Zhender interferometer was also used to investigate two other phenomena, the first one is electrophoresis and the second is the resonance mode of insects

From Cleanroom to Desktop: Emerging Micro-Nanofabrication Technology for Biomedical Applications

This review is motivated by the growing demand for low-cost, easy-to-use, compact-size yet powerful micro-nanofabrication technology to address emerging challenges of fundamental biology and translational medicine in regular laboratory settings. Recent advancements in the field benefit considerably from rapidly expanding material selections, ranging from inorganics to organics and from nanoparticles to self-assembled molecules. Meanwhile a great number of novel methodologies, employing off-the-shelf consumer electronics, intriguing interfacial phenomena, bottom-up self-assembly principles, etc., have been implemented to transit micro-nanofabrication from a cleanroom environment to a desktop setup. Furthermore, the latest application of micro-nanofabrication to emerging biomedical research will be presented in detail, which includes point-of-care diagnostics, on-chip cell culture as well as bio-manipulation. While significant progresses have been made in the rapidly growing field, both apparent and unrevealed roadblocks will need to be addressed in the future. We conclude this review by offering our perspectives on the current technical challenges and future research opportunities

Modular integration and on-chip sensing approaches for tunable fluid control polymer microdevices

228 p.Doktore tesi honetan mikroemariak kontrolatzeko elementuak diseinatu eta garatuko dira, mikrobalbula eta mikrosentsore bat zehazki. Ondoren, gailu horiek batera integratuko dira likido emari kontrolatzaile bat sortzeko asmotan. Helburu nagusia gailuen fabrikazio arkitektura modular bat frogatzea da, non Lab-on-a-Chip prototipoak garatzeko beharrezko fase guztiak harmonizatuz, Cyclic-Olefin-Polymer termoplastikozko mikrogailu merkeak pausu gutxi batzuetan garatuko diren, hauen kalitate industriala bermatuz. Ildo horretan, mikrogailuak prototipotik produkturako trantsizio azkar, erraz, errentagarri eta arriskurik gabeen bidez lortu daitezkeenetz frogatuko da