Shaun Berry, MIT Lincoln Laboratory
Sung Cho, University of Pittsburgh
Richard Fair, Duke University
Yves Fouillet, DTBS/SBSC/LCIV; CEA Léti Minatec
Robin Garrell, UCLA
Jason Heikenfeld, University of Cincinnati, ECE
Thomas Jones, University of Rochester
Kwan Hyoung Kang, POSTECH (Pohang University of Science and Technology)
ChangJin (CJ) Kim, UCLA
Fabian Klingbeil, University of Erlangen-Nuremberg
Tom Krupenkin, Univ. of Wisconsin
Stein Kuiper, Philips
Mathieu Maillard, Varioptic
Romaric Massard, Liquavista
Glen McHale, Nottingham Trent University
Kamran Mohseni, University of Colorado at Boulder
Frieder Mugele, University of Twente
Ali Nadim, Keck Graduate Institute
Athanasios Papathanasiou, National Technical University of Athens
Michael Pollack, Advanced Liquid Logic
Benjamin Shapiro, University Maryland
Aaron Wheeler, University of Toronto
Shaun Berry
Advanced Silicon Group
MIT Lincoln Laboratory
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Electrowetting Actuation for Microfluidic Devices
This talk will report on the fabrication and performance testing of micro-sized fluidic
devices that use electrowetting for the mechanism to control and transport liquid within
micro-channel structures. Using standard microfabrication techniques new and unique
pumping systems were developed that differ from the digital microfluidic systems that are
often associated with electrowetting. Continuous flow micropumps were developed for
aqueous liquids as well as non-aqueous liquids. In addition, drop generators and pumps to
drive individual drops in micro-channel structures were developed. |
Sung Kwon Cho
Mechanical Engineering and Materials Science
University of Pittsburgh
|
Manipulation of objects using EWOD-actuated bubbles
Bubbles are ubiquitous in everyday life. In particular, in the past decades since the
emergence of microfluidic technology, micro bubbles have been attracting much more
attention, not only bringing a great deal of interesting scientific/engineering issues but also
providing high potentials in many microfluidic applications. In this talk, a variety of micro
bubble operations will be presented along with underlying scientific issues. The first part
of the talk will deal with fundamental bubble operations such as transporting, splitting,
merging, and on-chip creating/eliminating of microbubbles utilizing the electrowetting and
electrolysis principles. Then, the talk will switch gears to more advanced bubble operations
in which EWOD-actuated bubbles are oscillating in harmony with acoustic excitations.
EWOD-actuated oscillating bubbles can provide novel microfluidic functionalities such as
particle carrier, mobile vortex generator and mixing enhancer. |
Richard Fair
Electrical and Computer Engineering
Duke University
|
Scaling of Digital Microfluidic Devices for Picoliter Applications
We report on the design and testing of picoliter digital microfluidic devices made in
electrowetting-on-dielectric technology. Commercial devices now becoming available
have been fabricated at microliter and nanoliter scales. Such devices are appropriate for
many applications, including diagnostic assays. However, scaling will be required for at
least two reasons: 1) reduced microfluidic device size for integration on silicon, and 2)
parallel biochemical processing for high throughput chemistry, such as DNA sequencingby-
synthesis. The parameters that must be considered in scaling device dimensions
include: 1) threshold voltage for droplet actuation, 2) droplet splitting voltage, 3) droplet
dispensing voltage from on-chip reservoirs, 4) voltage dependence of droplet velocity, and
5) mixing times.
Our approach has been to develop dimensional scaling rules based on a hydrodynamic
model of droplet actuation. We start with analyzing the force balance on a moving droplet
in an actuator. Included are the effects of contact angle hysteresis of the advancing and
receding portions of a droplet. These forces are balanced by the electrowetting force.
Scaling rules are developed for droplet splitting using both a static model and a dynamic
model. Conditions for uniform splitting are determined experimentally. Both splitting and
dispensing are found to scale as (t/εr(d/L))1/2. Actuators operating with 35-105 picoliter
volumes were fabricated and tested for actuation, splitting, and dispensing. The smallest
gap height was 7.5μm for 40μm electrodes (d/L=0.19). The actuators behaved according to
the scaling principles described above. |
Yves Fouillet
Technology for Biology and Health
DTBS/SBSC/LCIV; CEA Léti Minatec
|
Bio-Protocol Integration in Digital Microfluidic Chips
In few years, microfluidics has become an enabling technology especially for biological
or chemical applications. A wide range of applications are addressed such as life
science research, point of care analysis, food or environmental control. In each case,
functionalities and specifications are different and a variety of microfluidic techniques are
now available. One essential point that still must be addressed for future industrialization is
to succeed in whole protocol integration in a single chip or portable system. By analysing
different type of architecture and applications, microfluidic approach based on droplet
handling by electrowetting on dielectric (EWOD) is discussed and compared to other
fluidic techniques.
Different technologies for electrowetting devices are developed around the world:
microcontact printing, print circuit board or MEMS (micro-electro-mechanical-system
based on Integrated Circuit industry). In order to fabricate robust and reproducible chips,
our choice was to develop a whole fabrication process (from silicon wafer to complete
packaging) in MEMS clean room with industrial machines at 200mm wafer scale. One
issue is to set up optimum material and process for dielectric and hydrophobic layer which
is the main critical point of EWOD technology.
An example of complex bio-protocol that integrates several steps from sample
preparation to real time detection (taqMan PCR) is presented. This example illustrates the
ease of integration when using digital mircofluidics allowing chip design based on building
box type architecture. |
Robin Garrell
Chemistry and Biochemistry, Organic Chemistry
University of California, Los Angeles
|
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Jason Heikenfeld
Electrical & Computer Engineering
University of Cincinnati
|
Electrowetting Optics at University of Cincinnati
Recent progress of electrowetting optics at University of Cincinnati will be presented. |
Kwan H. Kang
Mechanical Engineering
POSTECH (Pohang University of Science and Technology)
|
Hydrodynamic Flows in AC Electrowetting
Hydrodynamic flows are generated inside a droplet in electrowetting when an AC
voltage is applied. In order to find out the characteristics and origin of the flows, we
investigated the flow pattern for a sessile droplet for various needle-electrode positions,
electrolyte concentrations, and applied electrical frequencies. Two distinct types of flows
were observed under current experimental conditions. In the typical experimental
condition, a quite fast flow appears in the low frequency range of about 10 Hz to 15 kHz.
A different type of flow is observed in the high frequency range of about 35 kHz to 256
kHz, but this frequency range depends significantly on the electrolyte concentration. Most
typically, the flow directions are opposite for the two flows. A shape oscillation of a
droplet was observed in the low-frequency range by a high-speed camera. The flow in the
low-frequency range is insensitive to the conductivity of the solution and may be caused
by the interfacial oscillation of a droplet. The flow at high frequency is very sensitive to
the conductivity of the solution and electrode position, so the high-frequency flow is
thought to be caused by some electrohydrodynamic effect. |
Thomas Jones
Electrical Engineering
University of Rochester
|
Variable Frequency Electromechanics of Liquids
The principal electrical force mechanisms exploited for droplet-based microfluidic
applications are electrowetting on dielectric-coated electrodes (EWOD) and liquid
dielectrophoresis (DEP). Though differing somewhat in physical origin, these electromechanical
mechanisms are interrelated via the frequency of the AC voltage. At low
frequency, slightly conductive liquids (such as aqueous media) behave like electrical
conductors, and EWOD is the operative mechanism. At high frequency, such liquids
behave like dielectric insulators where liquid DEP reigns. The electrical frequency that
demarcates the boundary between these two limits is a function of electrical conductivity
and may be derived from a simple RC circuit model. Because both amplitude and sign of
the net electrical force can be modulated merely by adjusting the frequency, some unique
schemes for microfluidic control arise. For example, simple electrode structures may be
used to shuttle liquid volumes back and forth between two equilibria merely by switching
the frequency between two values. Use of variable AC frequency as a control parameter
decreases the complexity of some microfluidic structures. Possible applications for
frequency-based actuation include displays, optoelectronic switches, lab-on-a-chip
schemes, and automated fluid separation apparatus. |
Chang Jin (CJ) Kim
Mechanical and Aerospace Engineering
University of California, Los Angeles
|
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Fabian Klingbeil
Mathematics
University of Erlangen-Nuremberg
|
A Phase-field Model for Electrowetting
We develop and analyze a model for electrowetting that combines the (Navier-)Stokes
system for fluid flow, a phase-field model of Cahn-Hilliard type for the movement of the
interface, a charge transport equation, and the potential equation of electrostatics. The
motion of contact line between liquid phases and wall is governed by generalized Navier
boundary condition as presented in (Qian, Wang and Sheng, A variational approach to the
moving contact line hydrodynamics, 2006, J. Fluid Mech., Vol. 564, pp. 333-360). The
existence of weak solutions of the resulting PDEs is proved for several cases in two and
three space dimensions.
Numerics examples illustrate the applicability in 2D (and 3D). First numerical experiments
indicate persistence of microscopic contact angle independent from voltage. Our
code allows simulation with time-dependent applied voltages (EWOD, lab-on-a-chip). No
additional data is needed (such as contact angle based on physical experiments). |
Tom Krupenkin
Mechanical Engineering
University of Wisconsin
|
Tunable Liquid Micromirror Based on Self-assembly of Janus Particles
In this work, we describe a conceptually simple optofluidic device: a concave reflector
made by covering the surface of an oil drop with anisotropically-functionalized, micronsized,
hexagonal micromirrors ("Janus tiles"). When this liquid mirror is deposited on a
suitably-patterned transparent electrode its focal length and axial position can be controlled
electrically using electrowetting phenomenon. The liquid mirror is mechanically robust
and retains its integrity even at high levels of vibrational excitation of the interface. The
use of reflection instead of refraction overcomes the limited available refractive-index
contrast between pairs of density-matched liquids allowing stronger focusing than is
possible for a liquid lens of the same geometry. This element could form the basis of
optical instruments with novel functionality - for example a dynamic 3D projector; i.e. a
light source which can scan an image onto a moving non-planar focal surface. Janus tiles
with complex optical properties can be manufactured using our approach thus potentially
enabling a wide range of novel optical elements. |
Stein Kuiper
Liquid Lenses
Philips
|
Fluids for Electrowetting
Fluids form the heart of electrowetting devices. The choice of fluids not only determines
the electrowetting performance, but also device-specific properties. Changing the
combination of two fluids to meet with the required device specifications usually leads to
unwanted changes in other specifications. How to increase the zoom factor of an
electrowetting camera without causing a density mismatch, making it slow or risking
frozen fluids on a cold day?
We searched for fluids with specific physical properties and good electrowetting
performance and obtained some very useful classes. Furthermore, we developed methods
to modify properties of the fluids without affecting other properties. Our research was
focused on optical devices, but many of the results are also applicable in other areas of
electrowetting. In the presentation we will try to give an overview of these results and
provide the audience with some tips and tricks that may help to improve their
electrowetting devices. |
Mathieu Maillard
Varioptic
|
Advanced Electrowetting for New Developments on Liquid Lens
The use of electrowetting for industrial applications like liquid lenses has been a
driving force for extensive developments on actuation predictability and reliability. It also
emphasized a constant need for basic knowledge on the electrowetting phenomenon, to be
able to improve the technology and provide innovations. This presentation will be focused
on recent results on the electrowetting stability and reliability and we will also present new
liquid lens developments enabling focus and tilt control. |
Romaric Massard
Liquavista
|
Optimising the Dielectric Performance of Electrowetting Displays
Liquavista is currently commercialising 1st generation displays based on the electrowetting
principle. Launch product will be small format displays for watches. To this end
the major focus of the company in recent times has been on transfer of materials and
process to manufacturing partners in the Far East. For future generation product in a much
broader applicaton space there is much scope for improving both electrical and optical
performance. Lowering drive voltage while maintaining the required device performance is
a key area. In this presentation the focus will be on reviewing the options and reporting
status with respect to the introduction of materials to improve dielectric performance. |
Glen McHale
Physics, Materials and Sensors
Nottingham Trent University
|
Resonant Oscillations of Liquid Marbles
A spherical conducting droplet in an alternating electric field is known to undergo
shape oscillations. When the droplet is supported by a substrate, the shape is no longer a
complete sphere, but shape resonances are still observed. To obtain a completely spherical
droplet some kind of levitation is needed and this has previously been provided by gas
films or magnetic or other external forces. Here, we report observations of shape
oscillations of a hydrophobic powder coated droplet of water - a so-called liquid marble.
When the powder is a spherical hydrophobic grain with a contact angle greater than 90
degrees, it adheres to the solid-water interface with more than half of its radius projecting
from the liquid thus ensuring the encapsulated water does not come into contact with any
substrate. These liquid marbles are highly mobile and can be regarded as completely nonwetting
droplets possessing contact angles of 180 degrees. Liquid marbles provide a new
mechanism to levitate droplets and provide droplets with small contact areas and mobile
contact lines for studies of shape oscillations. In this work, liquid marbles were created
using hydrophobic lycopodium and droplets of water containing potassium chloride. These
were excited into motion using an electrowetting-on-dielectric configuration with applied
frequency swept from 1 Hz to 250 Hz. Both an up-and-down rigid body motion and an
oscillation involving multiple nodes were observed and recorded using a high speed
camera. The square of the resonant frequency was found to be proportional to the cube of
the mode number, but with a volume dependent constant of proportionality. For
comparison, droplets on a hydrophobic planar surface were also investigated. This work
demonstrates the principle that oscillation modes of completely non-wetting droplets can
be studied using a simple powder coating approach without the need for any other
mechanism for levitation. |
Kamran Mohseni
Aerospace Engineering Sciences
University of Colorado at Boulder
|
Digitized Heat Transfer Using EWOD
This talk presents results on modeling, simulation, experimentation, and the use of
electrowetting on dielectric (EWOD) as the driving force for digitized heat transfer (DHT),
a novel approach to microscale thermal management in which system cooling is actively
achieved via the manipulation of an array of discrete microdroplets. Discrete droplets can
be created and manipulated by several techniques, including EWOD, dielectrophoresis,
continuous electrowetting, among others. In this work, thermal energy is transported by a
discrete array of electrostatically activated micro-droplets of liquid metals, alloys or
aqueous solutions with the potential of supporting significantly higher heat transfer rates
than classical air-cooled heat sinks. Numerical simulations and experimental results will be
presented for the heat transfer coefficient. It is found that DHT provides a much higher
heat transfer coefficient than a continuous flow. This was attributed to a forced
recirculation inside the droplet that is not available in continuous flow and provides an
added convective heat transfer normal to the wall. Detailed electrostatic force distribution
along the interface, Nusselt number graphs, and coupled hydrodynamic-electrostatic
simulations are also presented. The following selected publications from my group
provides further discussions on the topic of this presentation. |
Frieder Mugele
Applied Physics
University of Twente
|
Electrowetting of Complex Fluids and Complex Surfaces
In this presentation, I will provide an overview of recent experiments in which we
extend the use of EW to new applications: I will discuss (i) EW as a tool for characterizing
the droplet material properties such as interfacial tension and viscoelastic properties of
complex fluids; (ii) the use of EW in combination with conventional channel-based
microfluidic systems to control two-phase flow as well as microdrop generation in PDMSbased
flow focussing devices; (iii) contact angle hysteresis and depinning transitions of
microdrops. |
Ali Nadim
Applied Life Sciences
Keck Graduate Institute
|
Simulation of Electrowetting Actuation of Sessile Drops
After a brief overview of electrohydrodynamics including Maxwell's electric stress
tensor under AC fields where the medium has both conductive and dielectric characteristics,
we focus on the problem of electrowetting actuation of sessile drops on a
patterned array of electrodes with a thin dielectric coating. For both the case when the drop
is electrically grounded from below and when it is floating, we compute the electric field in
the vicinity of the drop over a range of frequencies and use the traction derived from the
Maxwell stress tensor to calculate the effective electrowetting force on the drop. At low
frequencies where the drop behaves like a perfect conductor, the results are compared with
previously derived lumped parameter models for the electrowetting force. When combined
with results for hydrodynamics of translating sessile drops, estimates can also be obtained
for the translational velocity of the actuated drops. (Joint work with James Sterling and
Maged Ismail.) |
Athanasios Papathanasiou
Chemical Engineering
National Technical University of Athens
|
Realistic Computations in Electrowetting: Interfacial Instabilities and Simulation
Beyond the Saturation
Based on our recent experimental and computational work on the connection between
dielectric breakdown strength and the contact angle saturation we present a simple model
/mechanism for simulating electrowetting even at high voltages i.e. beyond the saturation
limit. The breakdown strength of the dielectric material is still the critical parameter of the
model which successfully accounts for the dependence of the material dielectric properties
on the field strength distribution. And most importantly, no other material-dependant
fitting parameter is required for improving the computational predictions which have been
tested against many dielectrics ranging from Silicon Oxide to Parylene and PTFE.
In addition we employ finite element computations combined with computer aided
bifurcation analysis to illuminate shape transitions observed in captive drops in electrowetting.
Liquid droplets bridging the gap between two dielectric-coated horizontal
electrode plates suffer breakup shape transitions when a voltage applied between the
electrodes exceeds a threshold. Interestingly enough, broken liquid bridges (i.e. a pair of a
sessile and a pendant drop) can spontaneously rejoin if the voltage is still applied to the
electrodes.
We found that liquid bridges become unstable, as the applied voltage increases, at a
turning point bifurcation which signals their breakup. Moreover, we show that as the
droplets produced by the broken bridges elongate, approaching each other when the
applied voltage increases, they become unstable at a turning point; the turning point
bifurcation signals their rejoining even if the minimum distance between them is not zero. |
Michael Pollack
Advanced Liquid Logic
|
Lab-on-a-chip Platform Based on Digital Microfluidics
Digital microfluidics based on electrowetting provides a high level of flexibility, scalability,
and modularity for lab-on-a-chip applications. This talk will provide an overview
of the digital microfluidics "toolkit" which has been developed by Advanced Liquid Logic
over the past several years. The capabilities and implementation issues associated with
each of the diverse components of this toolkit will be presented and discussed. Examples
include droplet formation, droplet transport, droplet mixing, optical detection, magneticbead
handling, thermal control and traffic management. Integration of these components to
realize fully functional lab-on-a-chip systems will be discussed using several illustrative
examples. Applications including real-time PCR and ELISA will be briefly presented
along with a discussion of the challenges and opportunities of adapting biochemical
applications to digital microfluidic format. Finally,directions for future research will be
outlined with particular emphasis on real-world problems encountered in the
implementation of electrowetting-based digital microfluidics. |
Benjamin Shapiro
Aerospace Engineering
University Maryland
|
Electrowetting Dynamics: Modeling and Control
This talk will be on modeling and simulating the fluid dynamics of electrowetting, and
on algorithms for precision control of these dynamics.
Advanced 2-phase models will be presented that include contact angle saturation,
hysteresis, and a heuristic model for line pinning, along with sophisticated numerical
methods that accurately track moving liquid-gas interfaces by combining finite-element
techniques with level-sets to capture local topological changes (split / join events). These
models have been validated against experiments at UCLA (in collaboration with CJ Kim
and Robin Garrell).
Algorithms that control the fluid dynamics to, for example, precisely steer single
particles by manipulating actuators already found in existing electrowetting systems will
be shown, demonstrating that correct control can enable existing systems to display new
and powerful capabilities. The talk will close with a discussion of future research
directions to precisely control the shape of electro-wetted fluids. |
Aaron Wheeler
Chemistry
University of Toronto
|
Digital Microfluidics: from Fabrication to Applications
Digital microfluidics (DMF) is a fluid handling technique used to transport discrete
droplets of liquid across the surface of an array of electrodes. There is currently much
enthusiasm for applying DMF to biochemical applications; however, it is currently used in
only a few laboratories, world-wide. This is largely a function of accessibility- many
researchers do not have access to the clean-room facilities that are required for device
fabrication. Here, we present several new strategies, not requiring clean-rooms, for rapid
prototyping of DMF devices. In addition, we present the results of several applications of
DMF being developed in our lab, including DNA-, protein-, and cell-based assays, as well
as the manipulation of droplets in three-dimensions. |
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