Synthesis and Characterization of Cardanol-Based Non-Isocyanate Polyurethane.

This paper describes the synthesis of NIPU by using cardanol as starting material. A cardanol formaldehyde oligomer was first prepared through the reaction of cardanol and formaldehyde, catalyzed by citric acid. The resulting oligomer was then subjected to epoxidation with m-chloroperbenzoic acid to obtain an epoxide compound, which was subsequently used to fix carbon dioxide (CO2) and form a cyclic carbonate. Using this cyclic carbonate, along with an amine, cardanol-based isocyanate polyurethane (NIPU) was prepared. Different characterization methods, such as Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), and thermogravimetric analysis (TGA), were used to confirm the synthesis of the four intermediate products and NIPU in the reaction process. This study highlights the promise of bio-based NIPU as a sustainable alternative in a number of applications while offering insightful information on the synthesis and characterization of the material.

Light-stimulated micromotor swarms in an electric field with accurate spatial, temporal, and mode control.

Swarming, a phenomenon widely present in nature, is a hallmark of nonequilibrium living systems that harness external energy into collective locomotion. The creation and study of manmade swarms may provide insights into their biological counterparts and shed light to the rules of life. Here, we propose an innovative mechanism for rationally creating multimodal swarms with unprecedented spatial, temporal, and mode control. The research is realized in a system made of optoelectric semiconductor nanorods that can rapidly morph into three distinct modes, i.e., network formation, collectively enhanced rotation, and droplet-like clustering, pattern, and switch in-between under light stimulation in an electric field. Theoretical analysis and semiquantitative modeling well explain the observation by understanding the competition between two countering effects: the electrostatic assembly for orderliness and electrospinning-induced disassembly for disorderliness. This work could inspire the rational creation of new classes of reconfigurable swarms for both fundamental research and emerging applications.

Precise electrokinetic position and three-dimensional orientation control of a nanowire bioprobe in solution.

Owing to Brownian-motion effects, the precise manipulation of individual micro- and nanoparticles in solution is challenging. Therefore, scanning-probe-based techniques, such as atomic force microscopy, attach particles to cantilevers to enable their use as nanoprobes. Here we demonstrate a versatile electrokinetic trap that simultaneously controls the two-dimensional position with a precision of 20 nm and 0.5° in the three-dimensional orientation of an untethered nanowire, as small as 300 nm in length, under an optical microscope. The method permits the active transport of nanowires with a speed-dependent accuracy reaching 90 nm at 2.7 µm s-1. It also allows for their synchronous three-dimensional alignment and rotation during translocation along complex trajectories. We use the electrokinetic trap to accurately move a nanoprobe and stably position it on the surface of a single bacterial cell for sensing secreted metabolites for extended periods. The precision-controlled manipulation underpins developing nanorobotic tools for assembly, micromanipulation and biological measurements with subcellular resolution.

Portable Bulk-Water Disinfection by Live Capture of Bacteria with Divergently Branched Porous Graphite in Electric Fields.

Easy access to clean water is essential to functioning and development of modern society. However, it remains arduous to develop energy-efficient, facile, and portable water treatment systems for point-of-use (POU) applications, which is particularly imperative for the safety and resilience of society during extreme weather and critical situations. Here, we propose and validate a meritorious working scheme for water disinfection via directly capturing and removing pathogen cells from bulk water using strategically designed three-dimensional (3D) porous dendritic graphite foams (PDGFs) in a high-frequency AC field. The prototype, integrated in a 3D-printed portable water-purification module, can reproducibly remove 99.997% E. coli bacteria in bulk water at a few voltages with among the lowest energy consumption at 435.5 J·L-1. The PDGFs, costing $1.47 per piece, can robustly operate at least 20 times for more than 8 h in total without functional degradation. Furthermore, we successfully unravel the involved disinfection mechanism with one-dimensional Brownian dynamics simulation. The system is practically applied that brings natural water in Waller Creek at UT Austin to the safe drinking level. This research, including the working mechanism based on dendritically porous graphite and the design scheme, could inspire a future device paradigm for POU water treatment.

Enhanced Separation Performance of Hierarchically Porous Membranes Fabricated via the Combination of Crystallization Template and Foaming.

In this work, poly (vinylidene fluoride) (PVDF) hierarchically porous membranes (HPMs) with isolated large pores and continuous narrow nano-pores have been fabricated from its blend with poly (methyl methacrylate) (PMMA) based on the combination of crystallization template with chemical or supercritical CO2 foaming. On the one hand, the decomposition of azodicarbonamide (ADC, chemical foaming agent) or the release of CO2 can produce isolated large pores. On the other hand, PMMA is expelled during the isothermal crystallization of PVDF in their miscible blend, yielding narrow nano-pores upon etching with a selective solvent. In the case of supercritical CO2, the attained PVDF HPMs fail to improve separation performance because of the compact wall of isolated-large-pore and consequent poor connectivity of hierarchical pores. In the case of ADC, the optimal HPM exhibits much higher flux (up to 20 times) without any loss of selectivity compared with the reference only with nano-pores. The enhanced permeability can be attributed to the shorter diffusion length and lower diffusion barrier from isolated large pores, while the comparable selectivity is determined by narrow nano-pores in THE matrix.

Tunable Strong Coupling in Transition Metal Dichalcogenide Nanowires.

Subwavelength optical resonators with spatiotemporal control of light are essential to the miniaturization of optical devices. In this work, chemically synthesized transition metal dichalcogenide (TMDC) nanowires are exploited as a new type of dielectric nanoresonators to simultaneously support pronounced excitonic and Mie resonances. Strong light-matter couplings and tunable exciton polaritons in individual nanowires are demonstrated. In addition, the excitonic responses can be reversibly modulated with excellent reproducibility, offering the potential for developing tunable optical nanodevices. Being in the mobile colloidal state with highly tunable optical properties, the TMDC nanoresonators will find promising applications in integrated active optical devices, including all-optical switches and sensors.

2D-Material-Integrated Micromachines: Competing Propulsion Strategy and Enhanced Bacterial Disinfection.

2D transition-metal-dichalcogenide materials, such as molybdenum disulfide (MoS2 ) have received immense interest owing to their remarkable structure-endowed electronic, catalytic, and mechanical properties for applications in optoelectronics, energy storage, and wearable devices. However, 2D materials have been rarely explored in the field of micro/nanomachines, motors, and robots. Here, MoS2  with anatase TiO2  is successfully integrated into an original one-side-open hollow micromachine, which demonstrates increased light absorption of TiO2 -based micromachines to the visible region and the first observed motion acceleration in response to ionic media. Both experimentation and theoretical analysis suggest the unique type-II bandgap alignment of MoS2 /TiO2  heterojunction that accounts for the observed unique locomotion owing to a competing propulsion mechanism. Furthermore, by leveraging the chemical properties of MoS2 /TiO2 , the micromachines achieve sunlight-powered water disinfection with 99.999% Escherichia coli lysed in an hour. This research suggests abundant opportunities offered by 2D materials in the creation of a new class of micro/nanomachines and robots.

Dynamic Ultrasound Projector Controlled by Light.

Dynamic acoustic wavefront control is essential for many acoustic applications, including biomedical imaging and particle manipulation. Conventional methods are either static or in the case of phased transducer arrays are limited to a few elements and hence limited control. Here, a dynamic acoustic wavefront control method based on light patterns that locally trigger the generation of microbubbles is introduced. As a small gas bubble can effectively stop ultrasound transmission in a liquid, the optical images are used to drive a short electrolysis and form microbubble patterns. The generation of microbubbles is controlled by structured light projection at a low intensity of 65 mW cm-2 and only requires about 100 ms. The bubble pattern is thus able to modify the wavefront of acoustic waves from a single transducer. The method is employed to realize an acoustic projector that can generate various acoustic images and patterns, including multiple foci and acoustic phase gradients. Hydrophone scans show that the acoustic field after the modulation by the microbubble pattern forms according to the prediction. It is believed that combining a versatile optical projector to realize an ultrasound projector is a general scheme, which can benefit a multitude of applications based on dynamic acoustic fields.

Materials and Schemes of Multimodal Reconfigurable Micro/Nanomachines and Robots: Review and Perspective.

Mechanically programmable, reconfigurable micro/nanoscale materials that can dynamically change their mechanical properties or behaviors, or morph into distinct assemblies or swarms in response to stimuli have greatly piqued the interest of the science community due to their unprecedented potentials in both fundamental research and technological applications. To date, a variety of designs of hard and soft materials, as well as actuation schemes based on mechanisms including chemical reactions and magnetic, acoustic, optical, and electric stimuli, have been reported. Herein, state-of-the-art micro/nanostructures and operation schemes for multimodal reconfigurable micro/nanomachines and swarms, as well as potential new materials and working principles, challenges, and future perspectives are discussed.

Tunable Chiral Optics in All-Solid-Phase Reconfigurable Dielectric Nanostructures.

Subwavelength nanostructures with tunable compositions and geometries show favorable optical functionalities for the implementation of nanophotonic systems. Precise and versatile control of structural configurations on solid substrates is essential for their applications in on-chip devices. Here, we report all-solid-phase reconfigurable chiral nanostructures with silicon nanoparticles and nanowires as the building blocks in which the configuration and chiroptical response can be tailored on-demand by dynamic manipulation of the silicon nanoparticle. We reveal that the optical chirality originates from the handedness-dependent coupling between optical resonances of the silicon nanoparticle and the silicon nanowire via numerical simulations and coupled-mode theory analysis. Furthermore, the coexisting electric and magnetic resonances support strong enhancement of optical near-field chirality, which enables label-free enantiodiscrimination of biomolecules in single nanostructures. Our results not only provide insight into the design of functional high-index materials but also bring new strategies to develop adaptive devices for photonic and electronic applications.

Acceleration of Biomolecule Enrichment and Detection with Rotationally Motorized Opto-Plasmonic Microsensors and the Working Mechanism.

Vigorous research efforts have advanced the state-of-the-art nanosensors with ultrahigh sensitivity for bioanalysis. However, a dilemmatic challenge remains: it is extremely difficult to obtain nanosensors that are both sensitive and high-speed for the detection of low-concentration molecules in aqueous samples. Herein, we report how the controlled mechanical rotation (or rotary motorization) of designed opto-plasmonic microsensors can substantially and robustly accelerate the enrichment and detection speed of deoxyribonucleic acid (DNA) with retained high sensitivity. At least 4-fold augmentation of the capture speed of DNA molecules is obtained from a microsensor rotating at 1200 rpm. Theoretical analysis and modeling shed light on the underlying working mechanism, governed by the molecule-motor-flow interaction as well as its application range and limitation. This work provides a device scheme that alleviates the dilemmatic challenge in biomolecule sensing and offers the understanding of the complex interactions of molecules and moving microobjects in suspension. The results may assist the rational design of efficient microrobotic systems for the capture, translocation, sensing, and release of biocargoes.

Novel Method for Preparing a High-Performance Auxetic Foam Directly from Polymer Resin by a One-Pot CO2 Foaming Process.

So far, negative Poisson's ratio foam (auxetic foam) is usually prepared by the transformation of conventional polymer foam, and it is a challenge to prepare auxetic foam directly from polymer resin. In this work, a novel method based on the synergism between the phase transition of water and the permeability rate difference of the CO2 blowing agent from air in the foaming process is put forward to prepare auxetic foam directly from the polymer resin. Using this method, herein, nylon elastomer (NE) foam with auxetic behavior is successfully prepared from NE resin by a one-pot CO2 foaming method inside an autoclave aided by water; the obtained auxetic foam has a Poisson's ratio value of -1.29 and has excellent tensile cycle stability and energy absorption performance. This method breaks through the bottleneck for preparing auxetic foams from the polymer resin directly, which is also green and environment-friendly. It is believed that the abovementioned method also applies to other thermoplastic polymers, which paves a way for designing and preparing multifunctional auxetic foam materials in the future via a one-pot CO2 foaming process. Furthermore, this work first demonstrates that the transformation between auxetic foam and positive Poisson's ratio foam is reversible due to the closed cell structure, which provides an opportunity to reversibly adjust the performance and the shape of polymer foam materials.

Scalable Fabrication of Molybdenum Disulfide Nanostructures and their Assembly.

Molybdenum disulfide (MoS2 ) is a multifunctional material that can be used for various applications. In the single-crystalline form, MoS2 shows superior electronic properties. It is also an exceptionally useful nanomaterial in its polycrystalline form with applications in catalysis, energy storage, water treatment, and gas sensing. Here, the scalable fabrication of longitudinal MoS2 nanostructures, i.e., nanoribbons, and their oxide hybrids with tunable dimensions in a rational and well-reproducible fashion, is reported. The nanoribbons, obtained at different reaction stages, that is, MoO3 , MoS2 /MoO2 hybrid, and MoS2 , are fully characterized. The growth method presented herein has a high yield and is particularly robust. The MoS2 nanoribbons can readily be removed from its substrate and dispersed in solution. It is shown that functionalized MoS2 nanoribbons can be manipulated in solution and assembled in controlled patterns and directly on microelectrodes with UV-click-chemistry. Owing to the high chemical purity and polycrystalline nature, the MoS2 nanostructures demonstrate rapid optoelectronic response to wavelengths from 450 to 750 nm, and successfully remove mercury contaminants from water. The scalable fabrication and manipulation followed by light-directed assembly of MoS2 nanoribbons, and their unique properties, will be inspiring for device fabrication and applications of the transition metal dichalcogenides.

Infrared spectroscopy of live cells from a flowing solution using electrically-biased plasmonic metasurfaces.

Spectral cytopathology (SCP) is a promising label-free technique for diagnosing diseases and monitoring therapeutic outcomes using FTIR spectroscopy. In most cases, cells must be immobilized on a substrate prior to spectroscopic interrogation. This creates significant limitations for high throughput phenotypic whole-cell analysis, especially for the non-adherent cells. Here we demonstrate how metasurface-enhanced infrared reflection spectroscopy (MEIRS) can be applied to a continuous flow of live cell solution by applying AC voltage to metallic metasurfaces. By integrating metasurfaces with microfluidic delivery channels and attracting the cells to the metasurface via dielectrophoretic (DEP) force, we collect the infrared spectra of cells in real time within a minute, and correlate the spectra with simultaneously acquired images of the attracted cells. The resulting DEP-MEIRS technique paves the way for rapid SCP of complex cell-containing body fluids with low cell concentrations, and for the development of a wide range of label-free liquid biopsies.

Optical nanomanipulation on solid substrates via optothermally-gated photon nudging.

Constructing colloidal particles into functional nanostructures, materials, and devices is a promising yet challenging direction. Many optical techniques have been developed to trap, manipulate, assemble, and print colloidal particles from aqueous solutions into desired configurations on solid substrates. However, these techniques operated in liquid environments generally suffer from pattern collapses, Brownian motion, and challenges that come with reconfigurable assembly. Here, we develop an all-optical technique, termed optothermally-gated photon nudging (OPN), for the versatile manipulation and dynamic patterning of a variety of colloidal particles on a solid substrate at nanoscale accuracy. OPN takes advantage of a thin surfactant layer to optothermally modulate the particle-substrate interaction, which enables the manipulation of colloidal particles on solid substrates with optical scattering force. Along with in situ optical spectroscopy, our non-invasive and contactless nanomanipulation technique will find various applications in nanofabrication, nanophotonics, nanoelectronics, and colloidal sciences.

Light programmable micro/nanomotors with optically tunable in-phase electric polarization.

To develop active nanomaterials that can instantly respond to external stimuli with designed mechanical motions is an important step towards the realization of nanorobots. Herein, we present our finding of a versatile working mechanism that allows instantaneous change of alignment direction and speed of semiconductor nanowires in an external electric field with simple visible-light exposure. The light induced alignment switch can be cycled over hundreds of times and programmed to express words in Morse code. With theoretical analysis and simulation, the working principle can be attributed to the optically tuned real-part (in-phase) electrical polarization of a semiconductor nanowire in aqueous suspension. The manipulation principle is exploited to create a new type of microscale stepper motor that can readily switch between in-phase and out-phase modes, and agilely operate independent of neighboring motors with patterned light. This work could inspire the development of new types of micro/nanomachines with individual and reconfigurable maneuverability for many applications.

Portable Low-Pressure Solar Steaming-Collection Unisystem with Polypyrrole Origamis.

Solar steaming has emerged as a promising green technology that can address the global issue of scarcity of clean water. However, developing high-performance, cost-effective, and manufacturable solar-steaming materials, and portable solar steaming-collection systems for individuals remains a great challenge. Here, a one-step, low-cost, and mass-producible synthesis of polypyrrole (PPy) origami-based photothermal materials, and an original portable low-pressure controlled solar steaming-collection unisystem, offering synergetic high rates in both water evaporation and steam collection, are reported. Due to enhanced areas for vapor dissipation, the PPy origami improves the water evaporation rate by at least 71% to 2.12 kg m-2 h-1 from that of a planar structure and exhibits a solar-thermal energy conversion efficiency of 91.5% under 1 Sun. When further controlling the pressure to ≈0.17 atm in the steaming-collection unisystem, the water collection rate improves by up to 52% systematically and dramatically. Although partial energy is utilized toward obtaining low-pressure, evaluations show that the overall energy efficiency is improved remarkably in the low-pressure system compared to that in ambient pressure. Furthermore, the device demonstrates effective decontamination of heavy metals, bacteria, and desalination. This work can inspire new paradigms toward developing high-performance solar steaming technologies for individuals and households.

Visible light-gated reconfigurable rotary actuation of electric nanomotors.

Highly efficient and widely applicable working mechanisms that allow nanomaterials and devices to respond to external stimuli with controlled mechanical motions could make far-reaching impact to reconfigurable, adaptive, and robotic nanodevices. We report an innovative mechanism that allows multifold reconfiguration of mechanical rotation of semiconductor nanoentities in electric (E) fields by visible light stimulation. When illuminated by light in the visible-to-infrared regime, the rotation speed of semiconductor Si nanowires in E-fields can instantly increase, decrease, and even reverse the orientation, depending on the intensity of the applied light and the AC E-field frequency. This multifold rotational reconfiguration is highly efficient, instant, and facile. Switching between different modes can be simply controlled by the light intensity at an AC frequency. We carry out experiments, theoretical analysis, and simulations to understand the underlying principle, which can be attributed to the optically tunable polarization of Si nanowires in an aqueous suspension and an external E-field. Finally, leveraging this newly discovered effect, we successfully differentiate semiconductor and metallic nanoentities in a noncontact and nondestructive manner. This research could inspire a new class of reconfigurable nanoelectromechanical and nanorobotic devices for optical sensing, communication, molecule release, detection, nanoparticle separation, and microfluidic automation.

Novel Method for Preparing Auxetic Foam from Closed-Cell Polymer Foam Based on the Steam Penetration and Condensation Process.

Auxetic materials are a class of materials possessing a negative Poisson's ratio. Here, we established a novel method for preparing auxetic foam from closed-cell polymer foam based on the steam penetration and condensation (SPC) process. Using polyethylene (PE) closed-cell foam as an example, the foams treated by the SPC process presented a negative Poisson's ratio during stretching and compression testing. The effect of steam-treated temperature and time on the conversion efficiency of negative-Poisson's ratio foam was investigated, and the mechanism of the SPC method for forming a reentrant structure was discussed. The results indicated that the presence of enough steam within the cells was a critical factor for the negative Poisson's ratio conversion in the SPC process. The pressure difference caused by steam condensation was the driving force for the conversion from conventional closed-cell foam to the negative-Poisson's ratio foam. Furthermore, the applicability of the SPC process for fabricating auxetic foam was studied by replacing PE foam by polyvinyl chloride foam with a closed-cell structure or replacing water steam by ethanol steam. The results verified the universality of the SPC process for fabricating auxetic foams from conventional foams with a closed-cell structure. In addition, we explored the potential application of the obtained auxetic foams by the SPC process in the fabrication of shape-memory polymer materials.

Electric-Field-Guided Precision Manipulation of Catalytic Nanomotors for Cargo Delivery and Powering Nanoelectromechanical Devices.

We report a controllable and precision approach in manipulating catalytic nanomotors by strategically applied electric (E-) fields in three dimensions (3-D). With the high controllability, the catalytic nanomotors have demonstrated versatility in capturing, delivering, and releasing of cargos to designated locations as well as in situ integration with nanomechanical devices (NEMS) to chemically power the actuation. With combined AC and DC E-fields, catalytic nanomotors can be accurately aligned by the AC E-fields and effectively change their speeds instantly by the DC E-fields. Within the 3-D orthogonal microelectrode sets, the in-plane transport of catalytic nanomotors can be swiftly turned on and off, and these catalytic nanomotors can also move in the vertical direction. The interplaying nanoforces that govern the propulsion and alignment are investigated. The modeling of catalytic nanomotors proposed in previous works has been confirmed quantitatively here. Finally, the prowess of the precision manipulation of catalytic nanomotors by E-fields is demonstrated in two applications: the capture, transport, and release of cargos to prepatterned microdocks, and the assembly of catalytic nanomotors on NEMS to power the continuous rotation. The concepts and approaches reported in this work could further advance applications of catalytic nanomotors, e.g., for assembling and powering nanomachines, nanorobots, and complex NEMS devices.