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HighlightsTwo functionally different anisotropic layers are rationally assembled for highly selective and stretchable multidirectional strain sensors.Concurrently excellent selectivity, sensitivity, stretchability, and linearity up to 100% strain is demonstrated for the first time in a multidirectional strain sensor.A novel stepwise crack propagation mechanism is proposed to enable high stretchability and linearity. Flexible multidirectional strain sensors are crucial to accurately determining the complex strain states involved in emerging sensing applications. Although considerable efforts have been made to construct anisotropic structures for improved selective sensing capabilities, existing anisotropic sensors suffer from a trade-off between high sensitivity and high stretchability with acceptable linearity. Here, an ultrasensitive, highly selective multidirectional sensor is developed by rational design of functionally different anisotropic layers. The bilayer sensor consists of an aligned carbon nanotube (CNT) array assembled on top of a periodically wrinkled and cracked CNT–graphene oxide film. The transversely aligned CNT layer bridge the underlying longitudinal microcracks to effectively discourage their propagation even when highly stretched, leading to superior sensitivity with a gauge factor of 287.6 across a broad linear working range of up to 100% strain. The wrinkles generated through a pre-straining/releasing routine in the direction transverse to CNT alignment is responsible for exceptional selectivity of 6.3, to the benefit of accurate detection of loading directions by the multidirectional sensor. This work proposes a unique approach to leveraging the inherent merits of two cross-influential anisotropic structures to resolve the trade-off among sensitivity, selectivity, and stretchability, demonstrating promising applications in full-range, multi-axis human motion detection for wearable electronics and smart robotics.

Cooling in buildings is vital to human well-being but inevitability consumes significant energy, adding pressure on achieving carbon neutrality. Thermally superinsulating aerogels are promising to isolate the heat for more energy-efficient cooling. However, most aerogels tend to absorb the sunlight for unwanted solar heat gain, and it is challenging to scale up the aerogel fabrication while maintaining consistent properties. Herein, we develop a thermally insulating, solar-reflective anisotropic cooling aerogel panel containing in-plane aligned pores with engineered pore walls using boron nitride nanosheets by an additive freeze-casting technique. The additive freeze-casting offers highly controllable and cumulative freezing dynamics for fabricating decimeter-scale aerogel panels with consistent in-plane pore alignments. The unique anisotropic thermo-optical properties of the nanosheets combined with in-plane pore channels enable the anisotropic cooling aerogel to deliver an ultralow out-of-plane thermal conductivity of 16.9 mW m −1 K −1 and a high solar reflectance of 97%. The excellent dual functionalities allow the anisotropic cooling aerogel to minimize both parasitic and solar heat gains when used as cooling panels under direct sunlight, achieving an up to 7 °C lower interior temperature than commercial silica aerogels. This work offers a new paradigm for the bottom-up fabrication of scalable anisotropic aerogels towards practical energy-efficient cooling applications. Scaling up anisotropic freeze-casting processes can be challenging due to the temperature gradient farther from the cold source. Here, authors report an additive freeze-casting technique able to produce large-scale aerogel panels and demonstrate it towards practical passive cooling applications.

HighlightsHighly porous aerogel with longitudinally aligned channels and whisker-like ligaments is constructed by solvent-assisted unidirectional freezing.The thermal insulation and solar reflection capabilities of the composite aerogel reach a state-of-the-art level.The composite aerogel capable of infrared stealth and temperature preservation presents great potential for application in energy-saving buildings.With the mandate of worldwide carbon neutralization, pursuing comfortable living environment while consuming less energy is an enticing and unavoidable choice. Novel composite aerogels with super thermal insulation and high sunlight reflection are developed for energy-efficient buildings. A solvent-assisted freeze-casting strategy is used to produce boron nitride nanosheet/polyvinyl alcohol (BNNS/PVA) composite aerogels with a tailored alignment channel structure. The effects of acetone and BNNS fillers on microstructures and multifunctional properties of aerogels are investigated. The acetone in the PVA suspension enlarges the cell walls to suppress the shrinkage, giving rise to a lower density and a higher porosity, accompanied with much diminished heat conduction throughout the whole product. The addition of BNNS fillers creates whiskers in place of disconnected transverse ligaments between adjacent cell walls, further ameliorating the thermal insulation transverse to the cell wall direction. The resultant BNNS/PVA aerogel delivers an ultralow thermal conductivity of 23.5 mW m−1 K−1 in the transverse direction. The superinsulating aerogel presents both an infrared stealthy capability and a high solar reflectance of 93.8% over the whole sunlight wavelength, far outperforming commercial expanded polystyrene foams with reflective coatings. The anisotropic BNNS/PVA composite aerogel presents great potential for application in energy-saving buildings.

Over the past decade, the continuous development of soft multifunctional sensors capable of detecting important physical stimuli such as strain, pressure and temperature underpins the 4th industrial revolution of society. In particular, tremendous research efforts have been directed towards improving the sensing performance of the soft multifunctional sensors in terms of their sensitivity, sensing range, linearity, response time and durability. Nevertheless, several key requirements essential to the commercialization of soft multifunctional sensors remain unresolved and preserve as great challenges to date. One requirement is the simultaneous detection of the magnitudes and the directions of different mechanical stimuli applied to the sensors. Another requirement is to realize the concurrent detection and decoupling of multiple stimuli without interferences. In this thesis, novel multifunctional sensors based on one-dimensional (1D) carbon nanofibers (CNFs) are developed via a facile, low-cost, and scalable electrospinning technique to address the above challenges.Among various materials used to fabricate the soft multifunctional sensors, carbon nanomaterials are superior to their metallic counterparts because of their abundance in Earth, good electrical and thermal conductivities, and ease to be functionalized. Electrospun CNFs stand out as the best amidst various carbon nanomaterials for fabricating soft multifunctional sensors owing to their distinct advantages of scalability, processability and low fabrication cost. In addition, CNFs of unique morphologies and thus of novel properties can be easily fabricated by adopting simple modifications to the electrospinning apparatus. In this thesis, a novel multidirectional strain sensor is first developed using the aligned electrospun carbon nanofiber (ACNF) film/ polydimethylsiloxane (PDMS) composite. Compared to conventional soft strain sensors only capable of measuring strains in a uniaxial direction, the ACNF-based strain sensor demonstrates a unique ability to detect multiaxial strains. It distinguishes the directions and magnitudes of strains with a remarkable selectivity of 3.33. Further, its unconventional applications are demonstrated by detecting multi-degrees-of-freedom synovial joint movements of the human body and monitoring wrist movements for systematic improvement of golf performance. Second, we present a flexible temperature sensor based on the ACNF film. The ACNF-based temperature sensor exhibits outstanding sensitivity of 1.52% °C−1 , the highest sensitivity among carbon material-based soft temperature sensors. More importantly, it shows high discriminability towards temperature amidst other unwanted stimuli and maintains its original performance even after repeated stretch/release cycles because of the highly-aligned structure. Last, we present a soft all resistive multifunctional sensor with stimulus discriminability produced solely using electrospun CNFs as the sensing materials. Unlike other reported multifunctional sensors with stimulus discriminability, it accomplishes the pressure and temperature stimuli discriminability using a single type of output signal, namely the electrical resistance, which is the most convenient digital signal to monitor and process among others for device applications. The CNF-based soft multifunctional sensor’s ability to simultaneously detect and decouple temperature and pressure stimuli is also demonstrated for novel applications as a skin-mountable sensing device and a flexible game controller. Overall, the novel utilization of 1D electrospun CNFs to effectively solve the state-of-the-art challenges of the soft multifunctional sensors presented here will bring our society one step closer to realizing the 4th industrial revolution.

During vesicular trafficking and release of enveloped viruses, the budding and fission processes dynamically remodel the donor cell membrane in a protein- or a lipid-mediated manner. In all cases, in addition to the generation or relief of the curvature stress, the buds recruit specific lipids and proteins from the donor membrane through restricted diffusion for the development of a ring-type raft domain of closed topology. Here, by reconstituting the bud topography in a model membrane, we demonstrate the preferential localization of cholesterol- and sphingomyelin-enriched microdomains in the collar band of the bud-neck interfaced with the donor membrane. The geometrical approach to the recapitulation of the dynamic membrane reorganization, resulting from the local radii of curvatures from nanometre-to-micrometre scales, offers important clues for understanding the active roles of the bud topography in the sorting and migration machinery of key signalling proteins involved in membrane budding. Budding processes on cell membranes involve distortions of surface geometry, driven by the sorting of membrane components. Here, the authors model a budding process and observe spontaneous reordering of materials in the areas of high curvature, especially around bud-necks, producing ring-raft type structures.

We show that the selective localization of cholesterol-rich domains and associated ganglioside receptors prefer to occur in the monolayer across continuous monolayer-bilayer junctions (MBJs) in supported lipid membranes. For the MBJs, glass substrates were patterned with poly(dimethylsiloxane) (PDMS) oligomers by thermally-assisted contact printing, leaving behind 3 nm-thick PDMS patterns. The hydrophobicity of the transferred PDMS patterns was precisely tuned by the stamping temperature. Lipid monolayers were formed on the PDMS patterned surface while lipid bilayers were on the bare glass surface. Due to the continuity of the lipid membranes over the MBJs, essentially free diffusion of lipids was allowed between the monolayer on the PDMS surface and the upper leaflet of the bilayer on the glass substrate. The preferential localization of sphingomyelin, ganglioside GM1 and cholesterol in the monolayer region enabled to develop raft microdomains through coarsening of nanorafts. Our methodology provides a simple and effective scheme of non-disruptive manipulation of the chemical landscape associated with lipid phase separations, which leads to more sophisticated applications in biosensors and as cell culture substrates.