Showing papers by "Michael G. Pollack published in 2002"

Electrowetting-based actuation of droplets for integrated microfluidics

Abstract: The serviceability of microfluidics-based instrumentation including ‘lab-on-a-chip’ systems critically depends on control of fluid motion. We are reporting here an alternative approach to microfluidics based upon the micromanipulation of discrete droplets of aqueous electrolyte by electrowetting. Using a simple open structure, consisting of two sets of opposing planar electrodes fabricated on glass substrates, positional and formational control of microdroplets ranging in size from several nanoliters to several microliters has been demonstrated at voltages between 15–100 V. Since there are no permanent channels or structures between the plates, the system is highly flexible and reconfigurable. Droplet transport is rapid and efficient with average velocities exceeding 10 cm s−1 having been observed. The dependence of the velocity on voltage is roughly independent of the droplet size within certain limits, thus the smallest droplets studied (∼3 nl) could be transported over 1000 times their length per second. Formation, mixing, and splitting of microdroplets was also demonstrated using the same microactuator structures. Thus, electrowetting provides a means to achieve high levels of functional integration and flexibility for microfluidic systems.

Apparatus for manipulating droplets by electrowetting-based techniques

Abstract: An apparatus is provided for manipulating droplets The apparatus is a single-sided electrode design in which all conductive elements are contained on one surface on which droplets are manipulated An additional surface can be provided parallel with the first surface for the purpose of containing the droplets to be manipulated Droplets are manipulated by performing electrowetting-based techniques in which electrodes contained on or embedded in the first surface are sequentially energized and de-energized in a controlled manner The apparatus enables a number of droplet manipulation processes, including merging and mixing two droplets together, splitting a droplet into two or more droplets, sampling a continuous liquid flow by forming from the flow individually controllable droplets, and iterative binary or digital mixing of droplets to obtain a desired mixing ratio

Dynamics of electro-wetting droplet transport

Abstract: A model is formulated to describe the dynamics of electro-wetting-induced transport of liquid droplets. The velocity of droplet transport as a function of actuation voltage is derived. The operating parameters include the viscosity of the droplet and the medium through which it actuates, contact-line friction, system geometry, and surface tension. Numerical coefficients are extracted from experimental data to represent the effect of operating parameters on electro-wetting dynamics. The power dissipation of droplet transport is analyzed which reveals the key limiting factors for device operation as well the effect of scaling on device power requirements. # 2002 Published by Elsevier Science B.V.

Methods for sampling a liquid flow

Abstract: In a method for sampling a continuous liquid flow, the liquid flow is supplied to a surface along an input flow path. The liquid flow is sampled by forming a sample droplet from a portion of the liquid flow. The sample droplet is moved along an analysis flow path to a processing area of the surface, where the sample droplet is processed. Discrete sample droplets are formed and moved using an electrowetting technique. A binary mixing apparatus and method are also provided. The apparatus comprises an array of electrodes, an electronic controller communicating with the electrodes, a sample droplet supply area communicating with the array, and an additive droplet supply area communicating with the array. The electronic controller alternately energizes and de-energizes selected electrodes to carry out droplet-to-droplet binary mixing operations to obtain one or more droplets having a target mixing ratio.