Electrowetting,as a well-known approach to increasing droplet wettability on a solid surface by electrical bias,has broad applications.However,it is limited by contact angle saturation at large voltage.Although severa...Electrowetting,as a well-known approach to increasing droplet wettability on a solid surface by electrical bias,has broad applications.However,it is limited by contact angle saturation at large voltage.Although several debated hypotheses have been proposed to describe it,the physical origin of contact angle saturation still remains obscure.In this work,the physical factors responsible for the onset of contact angle saturation are explored,and the correlated theoretical models are established to characterize electrowetting behavior.Combination of the proper 3-phase system employed succeeds in dropping the saturating contact angle below 25?,and validates that the contact angle saturation is not a result of devicerelated imperfection.展开更多
Contact angle hysteresis(CAH) is one of the significant physical phenomena in electrowetting on dielectric(EWOD).In this work, a theoretical model is proposed to characterize electrowetting evolution on substrates wit...Contact angle hysteresis(CAH) is one of the significant physical phenomena in electrowetting on dielectric(EWOD).In this work, a theoretical model is proposed to characterize electrowetting evolution on substrates with CAH, and the relationship among apparent contact angle, potential, and some other parameters is quantified. And this theory is also validated experimentally. The results indicate that our theory and equation based on energy balance succeed in describing the electrowetting response of potential with significant contact angle hysteresis. The CAH in EWOD, ranging from 0° to about 20° in electrowetting cycle, increases with the increase of voltage and climbs up to about 20° when voltage is increased to about 38 V, and then decreases to zero with the further increase of voltage.展开更多
Bistable electrowetting display(EWD)is a promising low-power electronic paper technology,where power is consumed only during the switching between two stable states;however,it is not required for state maintenance onc...Bistable electrowetting display(EWD)is a promising low-power electronic paper technology,where power is consumed only during the switching between two stable states;however,it is not required for state maintenance once switched.In this paper,a bistable electrowetting device with non-planar designed controlling electrodes is fabricated by a fully conventional photolithography process.The device has potential for video display applications with a controllable gray scale.The novel electrode design realizes a lower driving voltage and a higher contrast between two stable states than the EWDs with planar electrodes reported previously.展开更多
Unremitting efforts have been intensively making for pursuing the goal of the reversible transition of electrowetting owing to its vital importance to many practical applications,but which remains a major challenge fo...Unremitting efforts have been intensively making for pursuing the goal of the reversible transition of electrowetting owing to its vital importance to many practical applications,but which remains a major challenge for carbon nanotubes due to the irreversible electrochemical damage.Herein,we proposed a subtly method to prevent the CNT array from electrochemical damage by using liquid medium instead of air medium to form a liquid/liquid/solid triphase system.The dimethicone dynamically refills in CNT arrays after removing of voltage that makes the surface back to hydrophobic,which is an elegant way to not only decrease energy dissipation in electrowetting process but also obtain extra energy in reversible dewetting process.Repeated cycles of in situ experiments showed that more than four reversible electrowetting cycles could be achieved in air.It wo rth mention that the in situ reve rsible electro wetting voltage of the dimethicone infused CNT array has been lowered to 2 V from 7 V which is the electrowetting voltage for the pure CNT array.The surface of the dimethicone infused CNT array can maintain hydrophobicity with a contact angle of 145.6°after four cycles,compared with 148.1°of the initial state.Moreover,a novel perspective of theoretical simulations through the binding energy has been provided which proved that the charged CNTs preferred binding with water molecules thereby replacing the dimethicone molecules adsorbed on the CNTs,whereas reconnected with dimethicone after removing the charges.Our study provides distinct insight into dynamic reversible electrowetting on the nanostructured surface in air and supplies a way for precise control of wettability in surface chemistry,smart phase-change heat transfer enhancement,liquid lenses,microfluidics,and other chemical engineering applications.展开更多
Electrowetting has been proposed as a technique for manipulating dropletssurrounded by air or oil. In this paper, we discuss the modeling and simulation of thedroplet fission process between two parallel plates inside...Electrowetting has been proposed as a technique for manipulating dropletssurrounded by air or oil. In this paper, we discuss the modeling and simulation of thedroplet fission process between two parallel plates inside an electrowetting on dielectric (EWOD) device. Since the gap between the plates is small, we use the two-phaseHele-Shaw flow as a model. While there are several high order methods around, suchas the immersed interface methods [1, 2], we decide to use two first-order methods forsimplicity. A ghost-fluid (GF) method is employed to solve the governing equationsand a local level set method is used to track the drop interface. For comparison purposes, the same set of two-phase Hele-Shaw equations are also solved directly usingthe immersed boundary (IB) method. Numerical results are consistent with experimental observations reported in the literature.展开更多
Electrowetting technology,a microfluidic technology,has attracted more and more attention in recent years and has broad prospects in terms of microdroplet drive.In this paper,the dynamic contact angle theory is used t...Electrowetting technology,a microfluidic technology,has attracted more and more attention in recent years and has broad prospects in terms of microdroplet drive.In this paper,the dynamic contact angle theory is used to develop a numerical model to predict the droplet dynamic contact behavior and internal flow field under electrowetting.In particular,based on the established computational model of droplet force balance,the dynamic process of a droplet under electrowetting is analyzed,including the perspective of pressure variation and force balance inside the droplet.The results show that when the alternating current frequency increases from 50 Hz to 500 Hz,the amplitude of the oscillation waveform after droplet stabilization is 0.036 mm,0.016 mm,0.013 mm and 0.002 mm,while the relevant droplet oscillation period T is 11 ms,4 ms,2 ms and 1 ms,respectively.It is also found that the initial phase angle does not affect the droplet oscillation amplitude.In addition,the pressure on the droplet surface under alternating current electrowetting increases rapidly to the maximum value with resonant waveform oscillation,and the droplet will present different resonance modes under voltage stimulation.The higher the resonance mode is,the smaller the droplet oscillation amplitude is and the streamline at the interface will present an eddy current,in which the number of vortices matches the resonance mode.A high resonance mode corresponds to a small droplet amplitude,while there are more vortices with a smaller size.展开更多
The solid-liquid interface, which is ubiquitous in nature and our daily life, plays fundamental roles in a variety of physical-chemical-biological- mechanical phenomena, for example in lubrication, crystal growth, and...The solid-liquid interface, which is ubiquitous in nature and our daily life, plays fundamental roles in a variety of physical-chemical-biological- mechanical phenomena, for example in lubrication, crystal growth, and many biological reactions that govern the building of human body and the functioning of brain. A surge of interests in the moving contact line (MCL) problem, which is still going on today, can be traced back to 1970s primarily because of the exis- tence of the "Huh-Scriven paradox". This paper, mainly from a solid mechanics perspective, describes very briefly the multidisciplinary nature of the MCL problem, then summarizes some major advances in this exciting research area, and some future directions are presented.展开更多
In this study, the azo red dyes derived from p-n-alkyl aniline by the introduction of different alkyl groups having high solubility in dodecane were synthesized. Results indicated that the elementary properties of red...In this study, the azo red dyes derived from p-n-alkyl aniline by the introduction of different alkyl groups having high solubility in dodecane were synthesized. Results indicated that the elementary properties of red oil inks were 1) non-polarity;2) low viscosity (<3.0 cps);3) specified surface tension (<30 mN/m);4) intensity of visible absorption covering 480 - 540 nm;5) hue close to standard red (CIE(x, y) = 0.67, 0.33). We can conclude that these azo red dyes are applicable for electrowetting displays.展开更多
Surface tension plays a core role in dominating various surface and interface phenomena. For liquid metals with high melting temperature, a profound understanding of the behaviors of surface tension is crucial in indu...Surface tension plays a core role in dominating various surface and interface phenomena. For liquid metals with high melting temperature, a profound understanding of the behaviors of surface tension is crucial in industrial processes such as casting, welding, and solidification, etc. Recently, the room temperature liquid metal (RTLM) mainly composed of gallium-based alloys has caused widespread concerns due to its increasingly realized unique virtues. The surface properties of such materials are rather vital in nearly all applications involved from chip cooling, thermal energy harvesting, hydrogen generation, shape changeable soft machines, printed electronics to 3D fabrication, etc. owing to its pretty large surface tension of approximately 700 mN/m. In order to promote the research of surface tension of RTLM, this paper is dedicated to present an overview on the roles and mechanisms of surface tension of liquid metal and summarize the latest progresses on the understanding of the basic knowledge, theories, influencing factors and experimental measure- ment methods clarified so far. As a practical technique to regulate the surface tension of RTLM, the fimdamental principles and applications of electrowetting are also interpreted. Moreover, the unique phenomena of RTLM surface tension issues such as surface tension driven self- actuation, modified wettability on various substrates and the functions of oxides are discussed to give an insight into the acting mechanism of surface tension. Furthermore, future directions worthy of pursuing are pointed out.展开更多
We introduce a new type of actuator,the microhydraulic stepping actuator(MSA),which borrows design and operational concepts from biological muscle and stepper motors.MSAs offer a unique combination of power,efficiency...We introduce a new type of actuator,the microhydraulic stepping actuator(MSA),which borrows design and operational concepts from biological muscle and stepper motors.MSAs offer a unique combination of power,efficiency,and scalability not easily achievable on the microscale.The actuator works by integrating surface tension forces produced by electrowetting acting on scaled droplets along the length of a thin ribbon.Like muscle,MSAs have liquid and solid functional components and can displace a large fraction of their length.The 100μm pitch MSA presented here already has an output power density of over 200 W kg^(−1),rivaling the most powerful biological muscles,due to the scaling of surface tension forces,MSA’s power density grows quadratically as its dimensions are reduced.展开更多
The shape of liquid interfaces can be precisely controlled using electrowetting,an actuation mechanism which has been widely used for tunable optofluidic micro-optical components such as lenses or irises.We have expan...The shape of liquid interfaces can be precisely controlled using electrowetting,an actuation mechanism which has been widely used for tunable optofluidic micro-optical components such as lenses or irises.We have expanded the considerable flexibility inherent in electrowetting actuation to realize a variable optofluidic slit,a tunable and reconfigurable two-dimensional aperture with no mechanically moving parts.This optofluidic slit is formed by precisely controlled movement of the liquid interfaces of two highly opaque ink droplets.The 1.5mmlong slit aperture,with controllably variable discrete widths down to 45 mm,may be scanned across a length of 1.5mmwith switching times between adjacent slit positions of less than 120 ms.In addition,for a fixed slit aperture position,the width may be tuned to a minimum of 3 mmwith high uniformity and linearity over the entire slit length.This compact,purely fluidic device offers an electrically controlled aperture tuning range not achievable with extant mechanical alternatives of a similar size.展开更多
Digital microfluidics (DMF) is a versatile microfluidics technology that has significant application potential in the areas of automation and miniaturization. In DME discrete droplets containing samples and reagents...Digital microfluidics (DMF) is a versatile microfluidics technology that has significant application potential in the areas of automation and miniaturization. In DME discrete droplets containing samples and reagents are controlled to implement a series of operations via electrowetting-on-dielectric. This process works by apply- ing electrical potentials to an array of electrodes coated with a hydrophobic dielectric layer. Unlike microchannels, DMF facilitates precise control over multiple reaction processes without using complex pump, microvalve, and tubing networks. DMF also presents other distinct features, such as portability, less sample consumption, shorter chemical reaction time, flexibility, and easier combination with other technology types. Due to its unique advantages, DMF has been applied to a broad range of fields (e.g., chemistry, biology, medicine, and environment). This study reviews the basic principles of droplet actuation, configuration design, and fabrication of the DMF device, as well as discusses the latest progress in DMF from the biochemistry perspective.展开更多
This review article examines digital microfluidic systems that manipulate droplets through surface anisotropy.These systems are categorized as surface tension driven or contact line driven.Surface tension driven syste...This review article examines digital microfluidic systems that manipulate droplets through surface anisotropy.These systems are categorized as surface tension driven or contact line driven.Surface tension driven systems include electrowetting on dielectric,Marangoni flow on microheater arrays,and chemical gradient surfaces,whereas contact line driven systems include anisotropic ratchet conveyors,nanostructured Parylene ratchets,and tilted pillar arrays.This article describes the operating principles and outlines the fabrication procedures for each system.We also present new equations that unify several previous models of contact line driven systems.The strengths and weaknesses of each system are compared,with a focus on their ability to perform the generation,switching,fusion,and fission of droplets.Finally,we discuss current and potential future applications of these systems.展开更多
基金Project supported by the Fund from the Research Center of Optical Communications Engineering&Technology,Jiangsu Province,China(Grant No.ZSF0402)
文摘Electrowetting,as a well-known approach to increasing droplet wettability on a solid surface by electrical bias,has broad applications.However,it is limited by contact angle saturation at large voltage.Although several debated hypotheses have been proposed to describe it,the physical origin of contact angle saturation still remains obscure.In this work,the physical factors responsible for the onset of contact angle saturation are explored,and the correlated theoretical models are established to characterize electrowetting behavior.Combination of the proper 3-phase system employed succeeds in dropping the saturating contact angle below 25?,and validates that the contact angle saturation is not a result of devicerelated imperfection.
基金supported by the Natural Science Foundation of Jiangsu Province,China(Grant No.BK2011752)
文摘Contact angle hysteresis(CAH) is one of the significant physical phenomena in electrowetting on dielectric(EWOD).In this work, a theoretical model is proposed to characterize electrowetting evolution on substrates with CAH, and the relationship among apparent contact angle, potential, and some other parameters is quantified. And this theory is also validated experimentally. The results indicate that our theory and equation based on energy balance succeed in describing the electrowetting response of potential with significant contact angle hysteresis. The CAH in EWOD, ranging from 0° to about 20° in electrowetting cycle, increases with the increase of voltage and climbs up to about 20° when voltage is increased to about 38 V, and then decreases to zero with the further increase of voltage.
基金the National Natural Science Foundation of China(No.61621061)the National Key R&D Program of China(No.2016YFA0201902)。
文摘Bistable electrowetting display(EWD)is a promising low-power electronic paper technology,where power is consumed only during the switching between two stable states;however,it is not required for state maintenance once switched.In this paper,a bistable electrowetting device with non-planar designed controlling electrodes is fabricated by a fully conventional photolithography process.The device has potential for video display applications with a controllable gray scale.The novel electrode design realizes a lower driving voltage and a higher contrast between two stable states than the EWDs with planar electrodes reported previously.
基金the National Natural Science Foundation of China(Nos.51706191,21673197,21621091,21975209)the National Key R&D Program of China(No.2018YFA0209500)+1 种基金the Fundamental Research Funds for the Central Universities(No.20720190037)the Natural Science Foundation of Fujian Province of China(No.2018J06003)。
文摘Unremitting efforts have been intensively making for pursuing the goal of the reversible transition of electrowetting owing to its vital importance to many practical applications,but which remains a major challenge for carbon nanotubes due to the irreversible electrochemical damage.Herein,we proposed a subtly method to prevent the CNT array from electrochemical damage by using liquid medium instead of air medium to form a liquid/liquid/solid triphase system.The dimethicone dynamically refills in CNT arrays after removing of voltage that makes the surface back to hydrophobic,which is an elegant way to not only decrease energy dissipation in electrowetting process but also obtain extra energy in reversible dewetting process.Repeated cycles of in situ experiments showed that more than four reversible electrowetting cycles could be achieved in air.It wo rth mention that the in situ reve rsible electro wetting voltage of the dimethicone infused CNT array has been lowered to 2 V from 7 V which is the electrowetting voltage for the pure CNT array.The surface of the dimethicone infused CNT array can maintain hydrophobicity with a contact angle of 145.6°after four cycles,compared with 148.1°of the initial state.Moreover,a novel perspective of theoretical simulations through the binding energy has been provided which proved that the charged CNTs preferred binding with water molecules thereby replacing the dimethicone molecules adsorbed on the CNTs,whereas reconnected with dimethicone after removing the charges.Our study provides distinct insight into dynamic reversible electrowetting on the nanostructured surface in air and supplies a way for precise control of wettability in surface chemistry,smart phase-change heat transfer enhancement,liquid lenses,microfluidics,and other chemical engineering applications.
基金The work was supported in part by Chinese NSF Project 10431030,NSERC and MITACS(Canada).
文摘Electrowetting has been proposed as a technique for manipulating dropletssurrounded by air or oil. In this paper, we discuss the modeling and simulation of thedroplet fission process between two parallel plates inside an electrowetting on dielectric (EWOD) device. Since the gap between the plates is small, we use the two-phaseHele-Shaw flow as a model. While there are several high order methods around, suchas the immersed interface methods [1, 2], we decide to use two first-order methods forsimplicity. A ghost-fluid (GF) method is employed to solve the governing equationsand a local level set method is used to track the drop interface. For comparison purposes, the same set of two-phase Hele-Shaw equations are also solved directly usingthe immersed boundary (IB) method. Numerical results are consistent with experimental observations reported in the literature.
基金the Natural Science Foundation of Jiangsu Province (Grant No.BK2020194)the Basic Research Fund of Central University (Grant No.NS2022026)the Graduate Research and Practice Innovation Program (Grant No.xcxjh20220215)。
文摘Electrowetting technology,a microfluidic technology,has attracted more and more attention in recent years and has broad prospects in terms of microdroplet drive.In this paper,the dynamic contact angle theory is used to develop a numerical model to predict the droplet dynamic contact behavior and internal flow field under electrowetting.In particular,based on the established computational model of droplet force balance,the dynamic process of a droplet under electrowetting is analyzed,including the perspective of pressure variation and force balance inside the droplet.The results show that when the alternating current frequency increases from 50 Hz to 500 Hz,the amplitude of the oscillation waveform after droplet stabilization is 0.036 mm,0.016 mm,0.013 mm and 0.002 mm,while the relevant droplet oscillation period T is 11 ms,4 ms,2 ms and 1 ms,respectively.It is also found that the initial phase angle does not affect the droplet oscillation amplitude.In addition,the pressure on the droplet surface under alternating current electrowetting increases rapidly to the maximum value with resonant waveform oscillation,and the droplet will present different resonance modes under voltage stimulation.The higher the resonance mode is,the smaller the droplet oscillation amplitude is and the streamline at the interface will present an eddy current,in which the number of vortices matches the resonance mode.A high resonance mode corresponds to a small droplet amplitude,while there are more vortices with a smaller size.
基金supported by the National Natural Science Foundation of China(11372313)the Key Research Program of the Chinese Academy of Sciences(KJZD-EW-M01)+1 种基金the Instrument Developing Project ofthe CAS(Y2010031)the CAS/SAFEA International Partnership Program for Creative Research Teams
文摘The solid-liquid interface, which is ubiquitous in nature and our daily life, plays fundamental roles in a variety of physical-chemical-biological- mechanical phenomena, for example in lubrication, crystal growth, and many biological reactions that govern the building of human body and the functioning of brain. A surge of interests in the moving contact line (MCL) problem, which is still going on today, can be traced back to 1970s primarily because of the exis- tence of the "Huh-Scriven paradox". This paper, mainly from a solid mechanics perspective, describes very briefly the multidisciplinary nature of the MCL problem, then summarizes some major advances in this exciting research area, and some future directions are presented.
文摘In this study, the azo red dyes derived from p-n-alkyl aniline by the introduction of different alkyl groups having high solubility in dodecane were synthesized. Results indicated that the elementary properties of red oil inks were 1) non-polarity;2) low viscosity (<3.0 cps);3) specified surface tension (<30 mN/m);4) intensity of visible absorption covering 480 - 540 nm;5) hue close to standard red (CIE(x, y) = 0.67, 0.33). We can conclude that these azo red dyes are applicable for electrowetting displays.
文摘Surface tension plays a core role in dominating various surface and interface phenomena. For liquid metals with high melting temperature, a profound understanding of the behaviors of surface tension is crucial in industrial processes such as casting, welding, and solidification, etc. Recently, the room temperature liquid metal (RTLM) mainly composed of gallium-based alloys has caused widespread concerns due to its increasingly realized unique virtues. The surface properties of such materials are rather vital in nearly all applications involved from chip cooling, thermal energy harvesting, hydrogen generation, shape changeable soft machines, printed electronics to 3D fabrication, etc. owing to its pretty large surface tension of approximately 700 mN/m. In order to promote the research of surface tension of RTLM, this paper is dedicated to present an overview on the roles and mechanisms of surface tension of liquid metal and summarize the latest progresses on the understanding of the basic knowledge, theories, influencing factors and experimental measure- ment methods clarified so far. As a practical technique to regulate the surface tension of RTLM, the fimdamental principles and applications of electrowetting are also interpreted. Moreover, the unique phenomena of RTLM surface tension issues such as surface tension driven self- actuation, modified wettability on various substrates and the functions of oxides are discussed to give an insight into the acting mechanism of surface tension. Furthermore, future directions worthy of pursuing are pointed out.
基金This material is based upon work supported by the Assistant Secretary of Defense for Research and Engineering under Air Force Contract No.FA8721-05-C-0002 and/or FA8702-15-D-0001.
文摘We introduce a new type of actuator,the microhydraulic stepping actuator(MSA),which borrows design and operational concepts from biological muscle and stepper motors.MSAs offer a unique combination of power,efficiency,and scalability not easily achievable on the microscale.The actuator works by integrating surface tension forces produced by electrowetting acting on scaled droplets along the length of a thin ribbon.Like muscle,MSAs have liquid and solid functional components and can displace a large fraction of their length.The 100μm pitch MSA presented here already has an output power density of over 200 W kg^(−1),rivaling the most powerful biological muscles,due to the scaling of surface tension forces,MSA’s power density grows quadratically as its dimensions are reduced.
基金funded by the German Research Foundation DFG within the Priority Program Active Micro-optics(SPP 1337).
文摘The shape of liquid interfaces can be precisely controlled using electrowetting,an actuation mechanism which has been widely used for tunable optofluidic micro-optical components such as lenses or irises.We have expanded the considerable flexibility inherent in electrowetting actuation to realize a variable optofluidic slit,a tunable and reconfigurable two-dimensional aperture with no mechanically moving parts.This optofluidic slit is formed by precisely controlled movement of the liquid interfaces of two highly opaque ink droplets.The 1.5mmlong slit aperture,with controllably variable discrete widths down to 45 mm,may be scanned across a length of 1.5mmwith switching times between adjacent slit positions of less than 120 ms.In addition,for a fixed slit aperture position,the width may be tuned to a minimum of 3 mmwith high uniformity and linearity over the entire slit length.This compact,purely fluidic device offers an electrically controlled aperture tuning range not achievable with extant mechanical alternatives of a similar size.
文摘Digital microfluidics (DMF) is a versatile microfluidics technology that has significant application potential in the areas of automation and miniaturization. In DME discrete droplets containing samples and reagents are controlled to implement a series of operations via electrowetting-on-dielectric. This process works by apply- ing electrical potentials to an array of electrodes coated with a hydrophobic dielectric layer. Unlike microchannels, DMF facilitates precise control over multiple reaction processes without using complex pump, microvalve, and tubing networks. DMF also presents other distinct features, such as portability, less sample consumption, shorter chemical reaction time, flexibility, and easier combination with other technology types. Due to its unique advantages, DMF has been applied to a broad range of fields (e.g., chemistry, biology, medicine, and environment). This study reviews the basic principles of droplet actuation, configuration design, and fabrication of the DMF device, as well as discusses the latest progress in DMF from the biochemistry perspective.
基金This work was supported by National Science Foundation grant ECCS-1308025 Droplet Ratchets:Low Cost Digital Microfluidics.HRH would like to acknowledge the National Defense Science and Engineering Graduate Fellowship(NDSEG)for their support of this workFabrication of ARCs was performed at the Washington Nanofabrication Facility(WNF),a National Nanotechnology Coordinated Infrastructure(NNCI)site at the University of Washington,which is supported in part by the National Science Foundation(awards 1542101,1337840 and 0335765),the Washington Research Foundation,the M.J.Murdock Charitable Trust,Altatech,ClassOne Technology,GCE Market,Google and SPTS.
文摘This review article examines digital microfluidic systems that manipulate droplets through surface anisotropy.These systems are categorized as surface tension driven or contact line driven.Surface tension driven systems include electrowetting on dielectric,Marangoni flow on microheater arrays,and chemical gradient surfaces,whereas contact line driven systems include anisotropic ratchet conveyors,nanostructured Parylene ratchets,and tilted pillar arrays.This article describes the operating principles and outlines the fabrication procedures for each system.We also present new equations that unify several previous models of contact line driven systems.The strengths and weaknesses of each system are compared,with a focus on their ability to perform the generation,switching,fusion,and fission of droplets.Finally,we discuss current and potential future applications of these systems.