@article{erlenbach_mondal_ma_neumann_ma_holbery_dickey_2023, title={Flexible-to-Stretchable Mechanical and Electrical Interconnects}, volume={1}, ISSN={["1944-8252"]}, url={https://doi.org/10.1021/acsami.2c14260}, DOI={10.1021/acsami.2c14260}, abstractNote={Stretchable electronic devices that maintain electrical function when subjected to stress or strain are useful for enabling new applications for electronics, such as wearable devices, human-machine interfaces, and components for soft robotics. Powering and communicating with these devices is a challenge. NFC (near-field communication) coils solve this challenge but only work efficiently when they are in close proximity to the device. Alternatively, electrical signals and power can arrive via physical connections between the stretchable device and an external source, such as a battery. The ability to create a robust physical and electrical connection between mechanically disparate components may enable new types of hybrid devices in which at least a portion is stretchable or deformable, such as hinges. This paper presents a simple method to make mechanical and electrical connections between elastomeric conductors and flexible (or rigid) conductors. The adhesion at the interface between these disparate materials arises from surface chemistry that forms strong covalent bonds. The utilization of liquid metals as the conductor provides stretchable interconnects between stretchable and non-stretchable electrical traces. The liquid metal can be printed or injected into vias to create interconnects. We characterized the mechanical and electrical properties of these hybrid devices to demonstrate the concept and identify geometric design criteria to maximize mechanical strength. The work here provides a simple and general strategy for creating mechanical and electrical connections that may find use in a variety of stretchable and soft electronic devices.}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Erlenbach, Steven and Mondal, Kunal and Ma, Jinwoo and Neumann, Taylor V and Ma, Siyuan and Holbery, James D. and Dickey, Michael D.}, year={2023}, month={Jan} }
 @article{yang_nithyanandam_kanetkar_kwon_ma_im_oh_shamsi_wilkins_daniele_et al._2023, title={Liquid Metal Coated Textiles with Autonomous Electrical Healing and Antibacterial Properties}, volume={4}, ISSN={["2365-709X"]}, DOI={10.1002/admt.202202183}, abstractNote={Conductive textiles are promising for human–machine interfaces and wearable electronics. A simple way to create conductive textiles by coating fabric with liquid metal (LM) particles is reported. The coating process involves dip-coating the fabric into a suspension of LM particles at room temperature. Despite being coated uniformly after drying, the textiles remain electrically insulating due to the native oxide that forms on the LM particles. Yet, they can be rendered conductive by compressing the textile to rupture the oxide and thereby percolate the particles. Thus, compressing the textile with a patterned mold can pattern conductive circuits on the textile. The electrical conductivity of these circuits increases by coating more particles on the textile. Notably, the conductive patterns autonomously heal when cut by forming new conductive paths along the edge of the cut. The textiles prove to be useful as circuit interconnects, Joule heaters, and flexible electrodes to measure ECG signals. Further, the LM-coated textiles provide antimicrobial protection against Pseudomonas aeruginosa and Staphylococcus aureus. Such simple coatings provide a route to convert otherwise insulating textiles into electrical circuits with the ability to autonomously heal and provide antimicrobial properties.}, journal={ADVANCED MATERIALS TECHNOLOGIES}, author={Yang, Jiayi and Nithyanandam, Praneshnandan and Kanetkar, Shreyas and Kwon, Ki Yoon and Ma, Jinwoo and Im, Sooik and Oh, Ji-Hyun and Shamsi, Mohammad and Wilkins, Mike and Daniele, Michael and et al.}, year={2023}, month={Apr} }
 @article{ma_krisnadi_vong_kong_awartani_dickey_2023, title={Shaping a Soft Future: Patterning Liquid Metals}, volume={3}, ISSN={["1521-4095"]}, url={https://doi.org/10.1002/adma.202205196}, DOI={10.1002/adma.202205196}, abstractNote={This review highlights the unique techniques for patterning liquid metals containing gallium (e.g., eutectic gallium indium, EGaIn). These techniques are enabled by two unique attributes of these liquids relative to solid metals: 1) The fluidity of the metal allows it to be injected, sprayed, and generally dispensed. 2) The solid native oxide shell allows the metal to adhere to surfaces and be shaped in ways that would normally be prohibited due to surface tension. The ability to shape liquid metals into non-spherical structures such as wires, antennas, and electrodes can enable fluidic metallic conductors for stretchable electronics, soft robotics, e-skins, and wearables. The key properties of these metals with a focus on methods to pattern liquid metals into soft or stretchable devices are summari.}, journal={ADVANCED MATERIALS}, author={Ma, Jinwoo and Krisnadi, Febby and Vong, Man Hou and Kong, Minsik and Awartani, Omar M. and Dickey, Michael D.}, year={2023}, month={Mar} }
 @article{wang_zhang_shamsi_thelen_qian_ma_hu_dickey_2022, title={Tough and stretchable ionogels by in situ phase separation}, volume={21}, ISSN={["1476-4660"]}, url={https://doi.org/10.1038/s41563-022-01195-4}, DOI={10.1038/s41563-022-01195-4}, number={3}, journal={NATURE MATERIALS}, publisher={Springer Science and Business Media LLC}, author={Wang, Meixiang and Zhang, Pengyao and Shamsi, Mohammad and Thelen, Jacob L. and Qian, Wen and Ma, Jinwoo and Hu, Jian and Dickey, Michael D.}, year={2022}, month={Feb} }
 @article{neumann_kara_sargolzaeiaval_im_ma_yang_ozturk_dickey_2021, title={Aerosol Spray Deposition of Liquid Metal and Elastomer Coatings for Rapid Processing of Stretchable Electronics}, volume={12}, ISSN={["2072-666X"]}, url={https://doi.org/10.3390/mi12020146}, DOI={10.3390/mi12020146}, abstractNote={We report a spray deposition technique for patterning liquid metal alloys to form stretchable conductors, which can then be encapsulated in silicone elastomers via the same spraying procedure. While spraying has been used previously to deposit many materials, including liquid metals, this work focuses on quantifying the spraying process and combining it with silicones. Spraying generates liquid metal microparticles (~5 μm diameter) that pass through openings in a stencil to produce traces with high resolution (~300 µm resolution using stencils from a craft cutter) on a substrate. The spraying produces sufficient kinetic energy (~14 m/s) to distort the particles on impact, which allows them to merge together. This merging process depends on both particle size and velocity. Particles of similar size do not merge when cast as a film. Likewise, smaller particles (<1 µm) moving at the same speed do not rupture on impact either, though calculations suggest that such particles could rupture at higher velocities. The liquid metal features can be encased by spraying uncured silicone elastomer from a volatile solvent to form a conformal coating that does not disrupt the liquid metal features during spraying. Alternating layers of liquid metal and elastomer may be patterned sequentially to build multilayer devices, such as soft and stretchable sensors.}, number={2}, journal={MICROMACHINES}, publisher={MDPI AG}, author={Neumann, Taylor V. and Kara, Berra and Sargolzaeiaval, Yasaman and Im, Sooik and Ma, Jinwoo and Yang, Jiayi and Ozturk, Mehmet C. and Dickey, Michael D.}, year={2021}, month={Feb} }
 @article{lai_lu_wu_zhang_yang_ma_shamsi_vallem_dickey_2021, title={Elastic Multifunctional Liquid-Metal Fibers for Harvesting Mechanical and Electromagnetic Energy and as Self-Powered Sensors}, volume={11}, ISSN={["1614-6840"]}, DOI={10.1002/aenm.202100411}, abstractNote={Future wearable technologies and personal electronics may benefit from e-textiles that simultaneously possess high elasticity and multiple capabilities such as energy harvesting and sensing. Here, the first elastic multifunctional fiber that can scavenge mechanical energy from body motion and electromagnetic energy from surrounding electrical appliances is presented. In addition to converting multiple sources of waste energy into electricity, the fibers can also serve as self-powered tactile and biomechanical sensors. The fibers consist of hollow elastomeric fibers filled with liquid metal. The fibers harvest energy by the combination of triboelectricity (160 V m−1, 5 µA m−1, and ≈360 µW m−1) and induced electrification of the liquid metal (±8 V m−1 (60 Hz), ±1.4 µA m−1, and ≈8 µW m−1). The fibers are characterized and their utility for powering electronics and sensing biomechanical information is demonstrated. These fibers are further demonstrated as completely soft and stretchable components for human–machine interfaces, including keypads and wireless music controllers.}, number={18}, journal={ADVANCED ENERGY MATERIALS}, author={Lai, Ying-Chih and Lu, Hong-Wei and Wu, Hsing-Mei and Zhang, Dongguang and Yang, Jiayi and Ma, Jinwoo and Shamsi, Mohammad and Vallem, Veena and Dickey, Michael D.}, year={2021}, month={May} }
 @article{ma_bharambe_persson_bachmann_joshipura_kim_oh_patrick_adams_dickey_2021, title={Metallophobic Coatings to Enable Shape Reconfigurable Liquid Metal Inside 3D Printed Plastics}, volume={13}, ISSN={["1944-8252"]}, url={https://doi.org/10.1021/acsami.0c17283}, DOI={10.1021/acsami.0c17283}, abstractNote={Liquid metals adhere to most surfaces despite their high surface tension due to the presence of a native gallium oxide layer. The ability to change the shape of functional fluids within a three-dimensional (3D) printed part with respect to time is a type of four-dimensional printing, yet surface adhesion limits the ability to pump liquid metals in and out of cavities and channels without leaving residue. Rough surfaces prevent adhesion, but most methods to roughen surfaces are difficult or impossible to apply on the interior of parts. Here, we show that silica particles suspended in an appropriate solvent can be injected inside cavities to coat the walls. This technique creates a transparent, nanoscopically rough (10-100 nm scale) coating that prevents adhesion of liquid metals on various 3D printed plastics and commercial polymers. Liquid metals roll and even bounce off treated surfaces (the latter occurs even when dropped from heights as high as 70 cm). Moreover, the coating can be removed locally by laser ablation to create selective wetting regions for metal patterning on the exterior of plastics. To demonstrate the utility of the coating, liquid metals were dynamically actuated inside a 3D printed channel or chamber without pinning the oxide, thereby demonstrating electrical circuits that can be reconfigured repeatably.}, number={11}, journal={ACS APPLIED MATERIALS & INTERFACES}, publisher={American Chemical Society (ACS)}, author={Ma, Jinwoo and Bharambe, Vivek T. and Persson, Karl A. and Bachmann, Adam L. and Joshipura, Ishan D. and Kim, Jongbeom and Oh, Kyu Hwan and Patrick, Jason F. and Adams, Jacob J. and Dickey, Michael D.}, year={2021}, month={Mar}, pages={12709–12718} }
 @article{bharambe_ma_dickey_adams_2021, title={RESHAPE: A Liquid Metal-Based Reshapable Aperture for Compound Frequency, Pattern, and Polarization Reconfiguration}, volume={69}, ISSN={["1558-2221"]}, url={https://doi.org/10.1109/TAP.2020.3037803}, DOI={10.1109/TAP.2020.3037803}, abstractNote={We demonstrate a single-feed planar antenna capable of independently reconfiguring its operating frequency, radiation pattern, and polarization using stretchable, encapsulated liquid-metal (LM) parasitic elements. The LM is contained within elastomeric fibers that can be mechanically translated, stretched, or relaxed to alter the position or length of each conducting element on a 2-D surface, physically reshaping the metal on the antenna aperture. This eliminates several practical challenges associated with fluidic actuation of LM and makes the actuation scheme much faster and more reliable than other recent approaches. Using this scheme, the reshapable aperture (RESHAPE) design supports continuously reconfigurable operating frequencies from 2.45 to 6.5 GHz while supporting either linear $\hat {y}$ - or $\hat {\textrm {z}}$ -polarizations. At the same time, the radiation pattern can also be reconfigured in all planes, over a continuous range, to a maximum of ±45° away from the broadside direction for most frequencies. For all these possible states, the antenna maintains a 2:1 VSWR and a total efficiency of >60%. We explain the operation of the design at several frequencies, analyze the coverage area, and present measurements of a fabricated prototype.}, number={5}, journal={IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Bharambe, Vivek T. and Ma, Jinwoo and Dickey, Michael D. and Adams, Jacob J.}, year={2021}, month={May}, pages={2581–2594} }
 @misc{kwon_truong_krisnadi_im_ma_mehrabian_kim_dickey_2021, title={Surface Modification of Gallium-Based Liquid Metals: Mechanisms and Applications in Biomedical Sensors and Soft Actuators}, volume={3}, ISSN={["2640-4567"]}, DOI={10.1002/aisy.202000159}, abstractNote={This review focuses on surface modifications to gallium-based liquid metals (LMs), which are stretchable conductors with metallic conductivity and nearly unlimited extensibility due to their liquid nature. Despite the enormous surface tension of LM, it can be patterned into nonspherical shapes, such as wires, due to the presence of a native oxide shell. Incorporating inherently soft LM into elastomeric devices offers comfort, mechanical compliance, and stretchability. The thin oxide layer also enables the formation of stable liquid colloids and LM micro/nanosized droplets that do not coalesce easily. The oxide layer can also be exfoliated and chemically modified into semiconductor 2D materials to create and deposit atomically thin materials at room temperature. Thus, the interface and its manipulation are important. This review summarizes physical and chemical methods of modifying the surface of LM to tune its properties. The surface modification of LM provides unique applications, including use in soft biomedical sensors and actuators with mechanical properties similar to human tissue.}, number={3}, journal={ADVANCED INTELLIGENT SYSTEMS}, author={Kwon, Ki Yoon and Truong, Vi Khanh and Krisnadi, Febby and Im, Sooik and Ma, Jinwoo and Mehrabian, Nazgol and Kim, Tae-il and Dickey, Michael D.}, year={2021}, month={Mar} }
 @article{islam_li_moon_han_chung_ma_yoo_ko_oh_jung_et al._2020, title={Vertically Aligned 2D MoS2 Layers with Strain-Engineered Serpentine Patterns for High-Performance Stretchable Gas Sensors: Experimental and Theoretical Demonstration}, volume={12}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.0c17540}, abstractNote={Two-dimensional (2D) molybdenum disulfide (MoS2) with vertically aligned (VA) layers exhibits significantly enriched surface-exposed edge sites with an abundance of dangling bonds owing to its intrinsic crystallographic anisotropy. Such structural variation renders the material with exceptionally high chemical reactivity and chemisorption ability, making it particularly attractive for high-performance electrochemical sensing. This superior property can be further promoted as far as it is integrated on mechanically stretchable substrates well retaining its surface-exposed defective edges, projecting opportunities for a wide range of applications utilizing its structural uniqueness and mechanical flexibility. In this work, we explored VA-2D MoS2 layers configured in laterally stretchable forms for multifunctional nitrogen dioxide (NO2) gas sensors. Large-area (>cm2) VA-2D MoS2 layers grown by a chemical vapor deposition (CVD) method were directly integrated onto a variety of flexible substrates with serpentine patterns judiciously designed to accommodate a large degree of tensile strain. These uniquely structured VA-2D MoS2 layers were demonstrated to be highly sensitive to NO2 gas of controlled concentration preserving their intrinsic structural and chemical integrity, e.g., significant current response ratios of ∼160-380% upon the introduction of NO2 at a level of 5-30 ppm. Remarkably, they exhibited such a high sensitivity even under lateral stretching up to 40% strain, significantly outperforming previously reported 2D MoS2 layer-based NO2 gas sensors of any structural forms. Underlying principles for the experimentally observed superiority were theoretically unveiled by density functional theory (DFT) calculation and finite element method (FEM) analysis. The intrinsic high sensitivity and large stretchability of VA-2D MoS2 layers confirmed in this study are believed to be applicable in sensing diverse gas species, greatly broadening their versatility in stretchable and wearable technologies.}, number={47}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Islam, Md Ashraful and Li, Hao and Moon, Seokjin and Han, Sang Sub and Chung, Hee-Suk and Ma, Jinwoo and Yoo, Changhyeon and Ko, Tae-Jun and Oh, Kyu Hwan and Jung, YounJoon and et al.}, year={2020}, month={Nov}, pages={53174–53183} }
 @article{ma_lin_kim_ko_kim_oh_sun_gorman_voinov_smirnov_et al._2019, title={Liquid Metal Nanoparticles as Initiators for Radical Polymerization of Vinyl Monomers}, volume={8}, ISSN={["2161-1653"]}, url={https://doi.org/10.1021/acsmacrolett.9b00783}, DOI={10.1021/acsmacrolett.9b00783}, abstractNote={Sonication of gallium or gallium-based liquid metals in an aqueous solution of vinyl monomers leads to rapid free radical polymerization (FRP), without the need for conventional molecular initiators. Under ambient conditions, a passivating native oxide separates these metals from solution and renders the metal effectively inert. However, sonication generates liquid metal nanoparticles (LMNPs) of ∼100 nm diameter and thereby increases the surface area of the metal. The exposed metal initiates polymerization, which proceeds via a FRP mechanism and yields high molecular weight polymers that can form physical gels. Spin trapping EPR reveals the generation of free radicals. Time-of-flight secondary ion mass spectrometry measurements confirm direct polymer bonding to gallium, verifying the formation of surface-anchored polymer grafts. The grafted polymers can modify the interfacial properties, that is, the preference of the metal particles to disperse in aqueous versus organic phases. The polymer can also be degrafted and isolated from the particles using strong acid or base. The concept of physically disrupting passivated metal surfaces offers new routes for surface-initiated polymerization and has implications for surface modification, reduction reactions, and fabrication of mechanically responsive materials.}, number={11}, journal={ACS MACRO LETTERS}, publisher={American Chemical Society (ACS)}, author={Ma, Jinwoo and Lin, Yiliang and Kim, Yong-Woo and Ko, Yeongun and Kim, Jongbeom and Oh, Kyu Hwan and Sun, Jeong-Yun and Gorman, Christopher B. and Voinov, Maxim A. and Smirnov, Alex I. and et al.}, year={2019}, month={Nov}, pages={1522–1527} }