Humidity-Driven Switch in the Transparency of a Nanofiber Film for a Smart Window

Controlled Twill Surface Structure Endowing Nanofiber Composite Membrane Excellent Electromagnetic Interference Shielding

Inspired by the Chinese Knotting weave structure, an electromagnetic interference (EMI) nanofiber composite membrane with a twill surface was prepared. Poly(vinyl alcohol-co-ethylene) (Pva-co-PE) nanofibers and twill nylon fabric were used as the matrix and filter templates, respectively. A Pva-co-PE-MXene/silver nanowire (Pva-co-PE-MXene/AgNW, PMxAg) membrane was successfully prepared using a template method. When the MXene/AgNW content was only 7.4 wt% (PM7.4Ag), the EMI shielding efficiency (SE) of the composite membrane with the oblique twill structure on the surface was 103.9 dB and the surface twill structure improved the EMI by 38.5%. This result was attributed to the pre-interference of the oblique twill structure in the direction of the incident EM wave, which enhanced the probability of the electromagnetic waves randomly colliding with the MXene nanosheets. Simultaneously, the internal reflection and ohmic and resonance losses were enhanced. The PM7.4Ag membrane with the twill structure exhibited both an outstanding tensile strength of 22.8 MPa and EMI SE/t of 3925.2 dB cm-1. Moreover, the PMxAg nanocomposite membranes demonstrated an excellent thermal management performance, hydrophobicity, non-flammability, and performance stability, which was demonstrated by an EMI SE of 97.3% in a high-temperature environment of 140 °C. The successful preparation of surface-twill composite membranes makes it difficult to achieve both a low filler content and a high EMI SE in electromagnetic shielding materials. This strategy provides a new approach for preparing thin membranes with excellent EMI properties.

Self-Powered Terahertz Modulators Based on Metamaterials, Liquid Crystals, and Triboelectric Nanogenerators

6G communication mainly occurs in the THz band (0.1-10 THz), which can achieve excellent performance. Self-powered THz modulators are essential for achieving better conduction, modulation, and manipulation of THz waves. Herein, a self-powered terahertz modulator, which is based on metamaterials, liquid crystals (LCs), and rotary triboelectric nanogenerators (R-TENGs), is proposed to realize the driving of different array elements. The corresponding designs can achieve an integrated design and preparation method for dynamic spectrum-reconfigurable liquid crystal metamaterials. In addition, for the type of cross-structure metamaterial liquid crystal box, a phase modulation of 1 GHz is achieved at frequencies of 0.117 and 0.161 THz with modulation depths of 13 and 11%, respectively. Because the R-TENG with a multifan blade and circular electrodes can generate 18 peaks of electric output in every rotation, it can successfully provide sufficient frequency alternating-current electric energy to drive the terahertz modulator and achieve a self-powered function. Our findings lay a solid theoretical foundation for further building self-powered THz communication systems and promote the development of a theoretical system for LC-driving spectrum-reconfigurable devices in the THz domain.

Hydrochromic and piezochromic dual-responsive optical film derived from poloxamer and ethyl cellulose for visual fingerprints identification

Developing new materials that could identify fingerprint using the naked eye and observe the level 3 microscopic details is challenging. Here, we designed a novel hydrochromic and piezochromic dual-responsive optical film, which achieved the visual transparency transition. The performances of hydrochromic and piezochromic responses from high transparency to opaque whiteness were attributed to the introduction of poloxamer. The hygroscopic swelling of the disordered micelles led to light scattering, causing the hydrochromic response. The piezochromic response may be ascribed to the microcracks in the fragments of poloxamer crystals, which changed the refractive index of light. The fascinating combination of hydrochromic and piezochromic response was effectively applied in fingerprint identification. Hydrochromic response accurately recognized sweat pores, and piezochromic response could gradually reveal the ridges and valleys according to the different color of imprinted fingerprints. The film could identify fake fingerprints based on the differences in sweat pores between fake fingerprints and living fingers. More importantly, the film could easily detected not only the clear ridges but also the detailed sweat pores using the naked eye, indicating that the film has profound research significance in fingerprint analysis and liveness fingerprint detection.

Hydrochromic film for dynamic information storage using cellulose nanofibers and silica nanoparticles

A hydrochromic composite film was fabricated by incorporating silica nanoparticles (SiNPs) with cellulose nanofibers (CNFs). The CNF/SiNP composite film underwent a reversible change in transparency in response to external moisture variation. The CNFs improved the dimensional stability of the CNF/SiNP composite film and induced morphological differences in SiNP agglomerates, which control the water vapor condensation in a porous film. The condensed water in the pores reduced the difference in refractive index over the CNF/SiNP film, enhancing its transparency. The selective transparency of the composite film was challenged by printing CNF/SiNP inks at different composition ratios. The differing susceptibility of the printed patterns to moisture provided selective transparency at specific patterns, which can store dynamic information such as QR or numerical codes by simple water vapor adsorption and desorption.

Novel Green Reversible Humidity-Responsive Hemiaminal Dynamic Covalent Network for Smart Window

Recently, smart windows have attracted widespread attention on account of their unique features, yet traditional smart windows still rely on external energy support to accomplish dynamic reversible switching, which not only confines usage but also causes waste of energy. For this purpose, we have prepared hemiaminal dynamic covalent network (HDCN) film with outstanding flexibility and strength by a simple and low-cost method, in which the modulus is 206.28 MPa and the elongation at break is 39.02%. Additionally, the transition from a transparent to an opaque state is achieved when the film is stimulated by humidity, and the dynamic transformation of the film to different phases of transparency is obtained when the film is exposed to different relative humidities (60-99%). Most importantly, HDCN film fulfills the modern green requirements and enables complete dissolution in a certain mildly acidic solution, avoiding environmental pollution when the material is discarded due to loss of function. The dynamic tunability of HDCN film demonstrates great advantages and potential in smart windows and anticounterfeiting.