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Low-band-gap and thermally stable conjugated polymers developed using a dual acceptor–acceptor strategy and the addition of S and F atoms.

Liquid metal is a promising conductor material for producing soft and stretchable circuit "boards" that can enable next-generation electronics by electrically connecting and mechanically supporting electronic components. While liquid metal in general can be used to fabricate soft and stretchable circuits, magnetic liquid metal is appealing because it can be used for self-healing electronics and actuators by external magnetic fields. Liquid metal can be rendered into particles that can then be used for sensors and catalysts through sonication. We used this feature to produce "novel" conductive and magnetic particles. Mixing ferromagnetic iron particles into the liquid metal (gallium) produces conductive ferrofluids that can be rendered into gallium-coated iron particles by sonication. The gallium shell of the particles is extremely soft, while the rigid iron core can induce high friction in response to mechanical pressure; thus, hand-sintering of the particles can be used to directly write the conductive traces when the particles are cast as a film on elastic substrates. The surface topography of the particles can be manipulated by forming GaOOH crystals through sonication in DI water, thus resulting in nonwettable circuit boards. These gallium-coated iron particles dispersed in uncured elastomer can be assembled to form conductive microwires with the application of magnetic fields.

A bifunctional electrocatalyst based on heteroatoms doped VS2 was developed for electrocatalytic water splitting.

In this work, a facile and cost-effective approach to assemble metallic wires into two-dimensional (2D) and three-dimensional (3D) freestanding geometries by room-temperature welding is demonstrated. The low melting point of gallium (29.8 °C) enables the welding at room temperature without the aid of high-energy sources required for high-melting-point metals and alloys. The welding enables assembly of solid gallium wires into 2D and 3D geometries that could create freestanding architectures with multiple junctions along any inclined direction. These 2D and 3D freestanding metallic structures are freeze-cast in soft elastomers to obtain stretchable and soft devices: a 2D stretchable resistive and capacitive sensor patterned with parallel metal lines, a 2D stretchable capacitive sensor patterned with an interdigitated metal structure with capacitive changes on stretching in both x- and y-axes, and a 3D compressive sensor by assembly of liquid metal helices, which could sense foot pressure compression. We also developed a facile method to interconnect between soft circuits and external electronics, suppressing stress during mechanical deformation.

Shape memory composites are fascinating materials with the ability to preserve deformed shapes that recover when triggered by certain external stimuli. Although elastomers are not inherently shape memory materials, the inclusion of phase-change materials within the elastomer can impart shape memory properties. When this filler changes the phase from liquid to solid, the effective modulus of the polymer increases significantly, enabling stiffness tuning. Using gallium, a metal with a low melting point (29.8 °C), it is possible to create elastomeric materials with metallic conductivity and shape memory properties. This concept has been used previously in core-shell (gallium-elastomer) fibers and foams, but here, we show that it can also be implemented in elastomeric films containing microchannels. Such microchannels are appealing because it is possible to control the geometry of the filler and create metallically conductive circuits. Stretching the solidified metal fractures the fillers; however, they can heal by body heat to restore conductivity. Such conductive, shape memory sheets with healable conductivity may find applications in stretchable electronics and soft robotics.

For flexible displays, there is a desperate need for a broadband coatable polarizer that can absorb light in a specific direction. Conventional polarizers fabricated by the polymer stretching process are too thick (50-200 μm) to be used as polarizers that can be applied to antireflective films in flexible displays. For the development of the broadband coatable thin film polarizer, diacetylene (DA) amphiphiles containing I- or I3- are newly designed and synthesized, and the content of DA amphiphiles in the 4,6-decadiyne solvent is optimized to form a lyotropic liquid crystal (LLC) phase. Topochemical polymerization of uniaxially oriented iodine-based DA not only stabilizes the film but also broadens the polarization light region from 350 to 700 nm. The transfer and amplification of iodine and DA functions in uniaxially oriented thin films enable the fabrication of broadband coatable thin film polarizers.

Utilizing a newly programmed and synthesized heat storage mesogen (HSM) and reactive mesogen (RM), advanced heat managing polymer alloys that exhibit high thermal conductivity, high latent heat, and phase transition at high temperatures were developed for use as smart thermal energy harvesting and reutilization materials. The RM in the heat-managing RM-HSM polymer alloy was polymerized to form a robust polymeric network with high thermal conductivity. The phase-separated HSM domains between RM polymeric networks absorbed and released a lot of thermal energy in response to changes in the surrounding temperature. For the fabrication of smart heat-managing RM-HSM polymer alloys, the composition and polymerization temperature were optimized based on the constructed phase diagram and thermal energy managing properties of the RM-HSM mixture. From morphological investigation and thermal analysis, it was realized that the heat storage capacity of polymer alloys depends on the size of the phase-separated HSM domain. The structure-morphology-property relationship of the heat managing polymer alloys was built based on the combined techniques of thermal, scattering, and morphological analysis. The newly developed mesogen-based polymer alloys can be used as smart thermal energy-harvesting and reutilization materials.

Unexpected surge in online services causes poor performance and makes it challenging for the service provider to differentiate and serve genuine users. In this paper, we propose a novel approach using voluntary flushing to mitigate disruptions caused by surge traffic, such as distributed denial of service (DDoS) attacks on e-commerce websites. Voluntary flushing of customers has never been modeled because flushing was perceived negatively for customer service. We show that it may not be the case in today’s online services. We propose three queueing performance measures to evaluate the system and present optimal policies for flushing under various scenarios. We use DDoS attacks as use-case to present numerical analysis and discuss the implications of the flushing policies.

With the significance of heat management, recently, high thermal conducting polymers have attracted attention as promising polymeric matrix materials in miniaturized and flexible devices. Porphyrin-based reactive metallomesogens (PorV-x; x = -2H, -Ni, -Cu, and -Zn) were newly designed and synthesized for the fabrication of thermal conducting polymers. Self-assembled and subsequently polymerized PorV-x films exhibited excellent mechanical, chemical, and thermal stability. The thermal conducting properties of PorV-x films can be adjusted as desired by controlling the molecular planarity through metal core substitution. From the results of systematic experiments, it was realized that a deep understanding of the correlation between the supramolecular packing structure and thermal properties is essential for the precise control of the heat dissipating performance in advanced heat managing materials.