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  1. Abstract

    Binary nanoparticle (NP) superlattices exhibit distinct collective plasmonic, magnetic, optical, and electronic properties. Here, we computationally demonstrate how fluid-fluid interfaces could be used to self-assemble binary systems of NPs into 2D superlattices when the NP species exhibit different miscibility with the fluids forming the interface. We develop a basin-hopping Monte Carlo (BHMC) algorithm tailored for interface-trapped structures to rapidly determine the ground-state configuration of NPs, allowing us to explore the repertoire of binary NP architectures formed at the interface. By varying the NP size ratio, interparticle interaction strength, and difference in NP miscibility with the two fluids, we demonstrate the assembly of an array of exquisite 2D periodic architectures, including AB-, AB2-, and AB3-type monolayer superlattices as well as AB-, AB2-, A3B5-, and A4B6-type bilayer superlattices. Our results suggest that the interfacial assembly approach could be a versatile platform for fabricating 2D colloidal superlattices with tunable structure and properties.

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  2. Abstract

    The dry process is a promising fabrication method for all‐solid‐state batteries (ASSBs) to eliminate energy‐intense drying and solvent recovery steps and to prevent degradation of solid‐state electrolytes (SSEs) in the wet process. While previous studies have utilized the dry process to enable thin SSE films, systematic studies on their fabrication, physical and electrochemical properties, and electrochemical performance are unprecedented. Here, different fabrication parameters are studied to understand polytetrafluoroethylene (PTFE) binder fibrillation and its impact on the physio‐electrochemical properties of SSE films, as well as the cycling stability of ASSBs resulting from such SSEs. A counter‐balancing relation between the physio‐electrochemical properties and cycling stability is observed, which is due to the propagating behavior of PTFE reduction (both chemically and electrochemically) through the fibrillation network, resulting in cell failure from current leakage and ion blockage. By controlling PTFE fibrillation, a bilayer configuration of SSE film to enable physio‐electrochemically durable SSE film for both good cycling stability and charge storage capability of ASSBs is demonstrated.

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  3. Abstract

    Stimuli‐responsive hydrogels with programmable shapes produced by defined patterns of particles are of great interest for the fabrication of small‐scale soft actuators and robots. Patterning the particles in the hydrogels during fabrication generally requires external magnetic or electric fields, thus limiting the material choice for the particles. Acoustically driven particle manipulation, however, solely depends on the acoustic impedance difference between the particles and the surrounding fluid, making it a more versatile method to spatially control particles. Here, an approach is reported by combining direct acoustic force to align photothermal particles and photolithography to spatially immobilize these alignments within a temperature‐responsive poly(N‐isopropylacrylamide) hydrogel to trigger shape deformation under temperature change and light exposure. The spatial distribution of particles can be tuned by the power and frequency of the acoustic waves. Specifically, changing the spacing between the particle patterns and position alters the bending curvature and direction of this composite hydrogel sheet, respectively. Moreover, the orientation (i.e., relative angle) of the particle alignments with respect to the long axis of laser‐cut hydrogel strips governs the bending behaviors and the subsequent shape deformation by external stimuli. This acousto‐photolithography provides a means of spatiotemporal programming of the internal heterogeneity of composite polymeric systems.

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  4. Abstract

    Tobacco mosaic virus (TMV) was the first virus to be discovered and it is now widely used as a tool for biological research and biotechnology applications. TMV particles can be decorated with functional molecules by genetic engineering or bioconjugation. However, this can destabilize the nanoparticles, and/or multiple rounds of modification may be necessary, reducing product yields and preventing the display of certain cargo molecules. To overcome these challenges, we used phage display technology and biopanning to isolate a TMV‐binding peptide (TBPT25) with strong binding properties (IC50=0.73 μM, KD=0.16 μM), allowing the display of model cargos via a single mixing step. The TMV‐binding peptide is specific for TMV but does not recognize free coat proteins and can therefore be used to decorate intact TMV or detect intact TMV particles in crude plant sap.

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  5. Abstract

    Aromatic interactions are commonly involved in the assembly of naturally occurring building blocks, and these interactions can be replicated in an artificial setting to produce functional materials. Here we describe a colorimetric biosensor using co‐assembly experiments with plasmonic gold and surfactant‐like peptides (SLPs) spanning a wide range of aromatic residues, polar stretches, and interfacial affinities. The SLPs programmed in DDD−(ZZ)x−FFPC self‐assemble into higher‐order structures in response to a protease and subsequently modulate the colloidal dispersity of gold leading to a colorimetric readout. Results show the strong aggregation propensity of the FFPC tail without polar DDD head. The SLPs were specific to the target protease, i.e., Mpro, a biomarker for SARS‐CoV‐2. This system is a simple and visual tool that senses Mproin phosphate buffer, exhaled breath condensate, and saliva with detection limits of 15.7, 20.8, and 26.1 nM, respectively. These results may have value in designing other protease testing methods.

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  6. Abstract

    Crosslinking is a ubiquitous strategy in polymer engineering to increase the thermomechanical robustness of solid polymers but has been relatively unexplored in the context of π‐conjugated (semiconducting) polymers. Notwithstanding, mechanical stability is key to many envisioned applications of organic electronic devices. For example, the wide‐scale distribution of photovoltaic devices incorporating conjugated polymers may depend on integration with substrates subject to mechanical insult—for example, road surfaces, flooring tiles, and vehicle paint. Here, a four‐armed azide‐based crosslinker (“4Bx”) is used to modify the mechanical properties of a library of semiconducting polymers. Three polymers used in bulk heterojunction solar cells (donors J51 and PTB7‐Th, and acceptor N2200) are selected for detailed investigation. In doing so, it is shown that low loadings of 4Bx can be used to increase the strength (up to 30%), toughness (up to 75%), hardness (up to 25%), and cohesion of crosslinked films. Likewise, crosslinked films show greater physical stability in comparison to non‐crosslinked counterparts (20% vs 90% volume lost after sonication). Finally, the locked‐in morphologies and increased mechanical robustness enable crosslinked solar cells to have greater survivability to four degradation tests: abrasion (using a sponge), direct exposure to chloroform, thermal aging, and accelerated degradation (heat, moisture, and oxygen).

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  7. Abstract

    Untethered stimuli‐responsive soft materials with programmed sequential self‐folding are of great interest due to their ability to achieve task‐specific shape transformation with complex final configuration. Here, reversible and sequential self‐folding soft actuators are demonstrated by utilizing a temperature‐responsive nanocomposite hydrogel with different folding speeds but the same chemical composition. By varying the UV light intensity during the photo‐crosslinking of the nanocomposite hydrogel, different types of microstructures can be realized via phase separation mechanisms, which allow to control the folding speeds. The self‐folding structures are fabricated by integrating two dissimilar materials (i.e., a nanocomposite hydrogel and an elastomer) into hinge‐based bilayer structures via extrusion‐based 3D printing. It has been demonstrated that the folding kinetics can be accelerated by more than one order of magnitude due to the phase‐separated microstructure formed by the relatively weaker UV intensity (≈10 mW cm‐2) compared to the one formed by stronger UV intensity (≈100 mW cm‐2). 3D structures with sequential self‐folding capabilities are realized by prescribing actuation speeds and folding angles to specific hinges of the nanocomposite hydrogel. Sequential folding box and self‐locking latch structures are fabricated to demonstrate the ability to capture and hold objects underwater.

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  8. Abstract

    Poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a promising material because of its favorable electrical and mechanical properties, stability in ambient environments, and biocompatibility. It finds broad application in energy storage, flexible electronics, and bioelectronics. Additive manufacturing opens a plethora of new avenues to form and shape PEDOT:PSS, allowing for the rapid construction of customized geometries. However, there are difficulties in printing PEDOT:PSS while maintaining its attractive properties. A 3D printing method for PEDOT:PSS using a room‐temperature coagulation bath‐based direct ink writing technique is reported. This technique enables fabrication of PEDOT:PSS into parts that are of high resolution and high conductivity, while maintaining stable electrochemical properties. The coagulation bath can be further modified to improve the mechanical properties of the resultant printed part via a one‐step reaction. Furthermore, it is demonstrated that a simple post‐processing step allows the printed electrodes to strongly adhere to several substrates under aqueous conditions, broadening their use in bioelectronics. Employing 3D printing of PEDOT:PSS, a cortex‐wide neural interface is fabricated, and intracranial electrical stimulation and simultaneous optical monitoring of mice brain activity with wide field calcium imaging are demonstrated. This reported 3D‐printing technique eliminates the need for cumbersome experimental setups while offering desired material properties.

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  9. Abstract

    Thermo‐responsive polymers have been widely explored because of their diverse structures and functions in response to temperature stimuli. Great attention has been attracted to exploring and designing such polymers composites, which offer tremendous opportunities to build up a systematic understanding of their structure–function relationships and pave the ways for their extensive applications in electronics, soft robotics, and electrochemical energy storage devices. Here, we review the most recent research of thermal regulation in electrochemical energy storage devices (e.g., batteries, supercapacitors) via thermo‐responsive polymers. We summarize how battery components (i.e., electrolytes, separators, electrodes, or current collectors) can be coupled with thermo‐responsive polymers based on different operation mechanisms, such as volume expansion, polymerization, phase reversion, and de‐doping effects, to effectively prevent catastrophic thermal runaway. Different types of thermo‐responsive polymers are evaluated to compare their key features and/or limitations. This review is concluded with perspectives of future design strategies towards more effective thermo‐responsive polymers for battery thermal regulation.

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  10. Abstract

    Confining molecules in the nanoscale environment can lead to dramatic changes of their physical and chemical properties, which opens possibilities for new applications. There is a growing interest in liquefied gas electrolytes for electrochemical devices operating at low temperatures due to their low melting point. However, their high vapor pressure still poses potential safety concerns for practical usages. Herein, we report facile capillary condensation of gas electrolyte by strong confinement in sub-nanometer pores of metal-organic framework (MOF). By designing MOF-polymer membranes (MPMs) that present dense and continuous micropore (~0.8 nm) networks, we show significant uptake of hydrofluorocarbon molecules in MOF pores at pressure lower than the bulk counterpart. This unique property enables lithium/fluorinated graphite batteries with MPM-based electrolytes to deliver a significantly higher capacity than those with commercial separator membranes (~500 mAh g−1vs. <0.03 mAh g−1) at −40 °C under reduced pressure of the electrolyte.

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