@article{khan_trlica_so_valeri_dickey_2014, title={Influence of Water on the Interfacial Behavior of Gallium Liquid Metal Alloys}, volume={6}, ISSN={["1944-8252"]}, DOI={10.1021/am506496u}, abstractNote={Eutectic gallium indium (EGaIn) is a promising liquid metal for a variety of electrical and optical applications that take advantage of its soft and fluid properties. The presence of a rapidly forming oxide skin on the surface of the metal causes it to stick to many surfaces, which limits the ability to easily reconfigure its shape on demand. This paper shows that water can provide an interfacial slip layer between EGaIn and other surfaces, which allows the metal to flow smoothly through capillaries and across surfaces without sticking. Rheological and surface characterization shows that the presence of water also changes the chemical composition of the oxide skin and weakens its mechanical strength, although not enough to allow the metal to flow freely in microchannels without the slip layer. The slip layer provides new opportunities to control and actuate liquid metal plugs in microchannels-including the use of continuous electrowetting-enabling new possibilities for shape reconfigurable electronics, sensors, actuators, and antennas.}, number={24}, journal={ACS APPLIED MATERIALS & INTERFACES}, publisher={American Chemical Society (ACS)}, author={Khan, Mohammad R. and Trlica, Chris and So, Ju-Hee and Valeri, Michael and Dickey, Michael D.}, year={2014}, month={Dec}, pages={22467–22473} }
 @article{qusba_ramrakhyani_so_hayes_dickey_lazzi_2014, title={On the Design of Microfluidic Implant Coil for Flexible Telemetry System}, volume={14}, ISSN={["1558-1748"]}, DOI={10.1109/jsen.2013.2293096}, abstractNote={This paper describes the realization of a soft, flexible, coil fabricated by means of a liquid metal alloy encased in a biocompatible elastomeric substrate for operation in a telemetry system, primarily for application to biomedical implantable devices. Fluidic conductors are in fact well suited for applications that require significant flexibility as well as conformable and stretchable devices, such as implantable coils for wireless telemetry. A coil with high conductivity, and therefore low losses and high unloaded Q factor, is required to realize an efficient wireless telemetry system. Unfortunately, the conductivity of the liquid metal alloy considered-eutectic gallium indium (EGaIn)-is approximately one order of magnitude lower than gold or copper. The goal of this paper is to demonstrate that despite the lower conductivity of liquid metal alloys, such as EGaIn, compared with materials, such as copper or gold, it is still possible to realize an efficient biomedical telemetry system employing liquid metal coils on the implant side. A wireless telemetry system for an artificial retina to restore partial vision to the blind is used as a testbed for the proposed liquid metal coils. Simulated and measured results show that power transfer efficiency of 43% and 21% are obtained at operating distances between coils of 5 and 12 mm, respectively. Further, liquid metal based coil retains more than 72% of its performance (voltage gain, resonance bandwidth, and power transfer efficiency) when physically deformed over a curved surface, such as the surface of the human eye. This paper demonstrates that liquid metal-based coils for biomedical implant provide an alternative to stiff and uncomfortable traditional coils used in biomedical implants.}, number={4}, journal={IEEE SENSORS JOURNAL}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Qusba, Amit and RamRakhyani, Anil Kumar and So, Ju-Hee and Hayes, Gerard J. and Dickey, Michael D. and Lazzi, Gianluca}, year={2014}, month={Apr}, pages={1074–1080} }
 @article{ladd_so_muth_dickey_2013, title={3D Printing of Free Standing Liquid Metal Microstructures}, volume={25}, ISSN={["1521-4095"]}, DOI={10.1002/adma.201301400}, abstractNote={This paper describes a method to direct-write 3D liquid metal microcomponents at room temperature. The thin oxide layer on the surface of the metal allows the formation of mechanically stable structures strong enough to stand against gravity and the large surface tension of the liquid. The method is capable of printing wires, arrays of spheres, arches, and interconnects.}, number={36}, journal={ADVANCED MATERIALS}, publisher={Wiley}, author={Ladd, Collin and So, Ju-Hee and Muth, John and Dickey, Michael D.}, year={2013}, month={Sep}, pages={5081–5085} }
 @article{hayes_so_qusba_dickey_lazzi_2012, title={Flexible Liquid Metal Alloy (EGaIn) Microstrip Patch Antenna}, volume={60}, ISSN={["0018-926X"]}, DOI={10.1109/tap.2012.2189698}, abstractNote={This paper describes a flexible microstrip patch antenna that incorporates a novel multi-layer construction consisting of a liquid metal (eutectic gallium indium) encased in an elastomer. The combined properties of the fluid and the elastomeric substrate result in a flexible and durable antenna that is well suited for conformal antenna applications. Injecting the metal into microfluidic channels provides a simple way to define the shape of the liquid, which is stabilized mechanically by a thin oxide skin that forms spontaneously on its surface. This approach has proven sufficient for forming simple, single layer antenna geometries, such as dipoles. More complex fluidic antennas, particularly those featuring large, co-planar sheet-like geometries, require additional design considerations to achieve the desired shape of the metal. Here, a multi-layer patch antenna is fabricated using specially designed serpentine channels that take advantage of the unique rheological properties of the liquid metal alloy. The flexibility of the resulting antennas is demonstrated and the antenna parameters are characterized through simulation and measurement in both the relaxed and flexed states.}, number={5}, journal={IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Hayes, Gerard J. and So, Ju-Hee and Qusba, Amit and Dickey, Michael D. and Lazzi, Gianluca}, year={2012}, month={May}, pages={2151–2156} }
 @article{zhu_so_mays_desai_barnes_pourdeyhimi_dickey_2013, title={Ultrastretchable Fibers with Metallic Conductivity Using a Liquid Metal Alloy Core}, volume={23}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.201202405}, abstractNote={AbstractThe fabrication and characterization of fibers that are ultrastretchable and have metallic electrical conductivity are described. The fibers consist of a liquid metal alloy, eutectic gallium indium (EGaIn), injected into the core of stretchable hollow fibers composed of a triblock copolymer, poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] (SEBS) resin. The hollow fibers are easy to mass‐produce with controlled size using commercially available melt processing methods. The fibers are similar to conventional metallic wires, but can be stretched orders of magnitude further while retaining electrical conductivity. Mechanical measurements with and without the liquid metal inside the fibers show the liquid core has a negligible impact on the mechanical properties of the fibers, which is in contrast to most conductive composite fibers. The fibers also maintain the same tactile properties with and without the metal. Electrical measurements show that the fibers increase resistance as the fiber elongates and the cross sectional area narrows. Fibers with larger diameters change from a triangular to a more circular cross‐section during stretching, which has the appeal of lowering the resistance below that predicted by theory. To demonstrate their utility, the ultrastretchable fibers are used as stretchable wires for earphones and for a battery charger and perform as well as their conventional parts.}, number={18}, journal={ADVANCED FUNCTIONAL MATERIALS}, publisher={Wiley}, author={Zhu, Shu and So, Ju-Hee and Mays, Robin and Desai, Sharvil and Barnes, William R. and Pourdeyhimi, Behnam and Dickey, Michael D.}, year={2013}, month={May}, pages={2308–2314} }
 @article{khan_hayes_so_lazzi_dickey_2011, title={A frequency shifting liquid metal antenna with pressure responsiveness}, volume={99}, ISSN={["0003-6951"]}, DOI={10.1063/1.3603961}, abstractNote={This letter describes the fabrication and characterization of a shape shifting antenna that changes electrical length and therefore, frequency, in a controlled and rapid response to pressure. The antenna is composed of a liquid metal alloy (eutectic gallium indium) injected into microfluidic channels that feature rows of posts that separate adjacent segments of the metal. The initial shape of the antenna is stabilized mechanically by a thin oxide skin that forms on the liquid metal. Rupturing the skin merges distinct segments of the metal, which rapidly changes the length, and therefore frequency, of the antenna. A high speed camera elucidates the mechanism of merging and simulations model accurately the spectral properties of the antennas.}, number={1}, journal={APPLIED PHYSICS LETTERS}, publisher={AIP Publishing}, author={Khan, Mohammad Rashed and Hayes, Gerard J. and So, Ju-Hee and Lazzi, Gianluca and Dickey, Michael D.}, year={2011}, month={Jul} }
 @article{so_koo_dickey_velev_2012, title={Ionic Current Rectification in Soft-Matter Diodes with Liquid-Metal Electrodes}, volume={22}, ISSN={["1616-301X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84856758970&partnerID=MN8TOARS}, DOI={10.1002/adfm.201101967}, abstractNote={AbstractA soft‐matter‐based diode composed of hydrogel and liquid metal (eutectic gallium indium, EGaIn) is presented. The ability to control the thickness, and thus resistivity, of an oxide skin on the metal enables rectification. First, a simple model system with liquid‐metal/electrolyte‐solution/Pt interfaces is characterized. The electrically insulating oxide skin on the EGaIn electrode is reduced or oxidized further depending on the direction of the bias, thereby allowing unidirectional ionic current. The forward current of the diode increases as the conductivity of the electrolyte increases, whereas backward current depends on the pH of the medium in contact with the insulating oxide layer on the EGaIn electrode. As a result, the diode shows a higher rectification ratio (defined as the ratio of forward to backward current measured at the same absolute bias) with more conductive electrolyte at neutral pH. Replacement of the liquid electrolyte solution with a hydrogel improves the structural stability of the soft diode. The rectification performance also improves due to the increased ionic conductivity by the gel. Finally, a diode composed entirely of soft materials by replacing the platinum electrode with a second liquid‐metal electrode is presented. Contacting each liquid metal with a polyelectrolyte gel featuring different pH values provided asymmetry in the device, which is necessary for rectification. A hydrogel layer infused with a strong basic polyelectrolyte removes the insulating oxide layer, allowing one interface with the EGaIn electrode to be conductive regardless of the direction of bias. Thus, the oxide layer at the other interface rectifies the current.}, number={3}, journal={ADVANCED FUNCTIONAL MATERIALS}, publisher={Wiley}, author={So, Ju-Hee and Koo, Hyung-Jun and Dickey, Michael D. and Velev, Orlin D.}, year={2012}, month={Feb}, pages={625–631} }
 @article{koo_so_dickey_velev_2011, title={Towards All-Soft Matter Circuits: Prototypes of Quasi-Liquid Devices with Memristor Characteristics}, volume={23}, ISSN={["1521-4095"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-80051693085&partnerID=MN8TOARS}, DOI={10.1002/adma.201101257}, abstractNote={IO N We present a new class of electrically functional devices composed entirely of soft, liquid-based materials that display memristor-like characteristics. A memristor, or a “memory resistor”, is an electronic device that changes its resistive state depending on the current or voltage history through the device. Memristors may become the core of next generation memory devices because of their low energy consumption and high data density and performance. [ 1–3 ] Since the concept of memristors was theorized in 1971, [ 4 ] resistive switching memories have been fabricated from a variety of materials operating on magnetic, [ 5 ] thermal, [ 6 ] photonic, [ 7 ] electronic and ionic mechanisms. [ 3 , 8 , 9 ] Conventional memristive devices typically include metalinsulator-metal (M-I-M) junctions composed of rigid stacks of fi lms fabricated by multiple vacuum-deposition steps, often at high temperature. The most common “insulator” materials in M-I-M memristor junctions are inorganic metal oxides such as TiO 2 [ 10 ] and NiO. [ 11 ] Conducting pathways can form by current through such layers. Solid electrolytes between metal electrodes can also be used to create resistance switches (e.g., Ag/ Ag 2 S/Pt), in which conductive metal fi laments that bridge the two electrodes can be formed or annihilated on demand. [ 3 , 9 ] Memristive circuits composed of organic materials have some advantages over conventional metal oxides due to their ease of processing, light weight, and low cost. A variety of organic materials such as homogeneous polymers, small-molecule or nanoparticle doped polymers, and organic donor-acceptor complexes have been evaluated as components in memory switching devices. [ 12 ] We report new controllably bi-stable memristor-like devices fabricated entirely from liquid-based materials. These soft and fl exible devices are built from liquid metal and hydrogels that are used routinely in laboratories for hosting biological molecules and supporting cell growth. Hydrogels are soft, moldable and bio-compatible media similar to biological systems with high ion mobility due to the high water content ( > 90% water). [ 13 , 14 ] The ionic properties of the gels can be tuned by inclusion of polyelectrolytes that are immobilized via entanglement within the gel network. Hydrogels doped with polyelectrolytes have been utilized for fabricating electronic devices such as diodes and photovoltaic cells. [ 13 , 15 , 16 ] The electrodes of these devices, however, are rigid metals such as platinum and}, number={31}, journal={ADVANCED MATERIALS}, publisher={Wiley}, author={Koo, Hyung-Jun and So, Ju-Hee and Dickey, Michael D. and Velev, Orlin D.}, year={2011}, month={Aug}, pages={3559-+} }