Additive manufacturing of eco-friendly building insulation materials by recycling pulp and paper.

Thermal insulation materials by recycling pulp and paper wastes play an important role in environmental sustainability of green buildings. As society is pursuing the goal of zero carbon emissions, it is highly desirable to use eco-friendly materials and manufacturing technologies for building insulation envelopes. Here we report additive manufacturing of flexible and hydrophobic insulation composites from recycled cellulose-based fibers and silica aerogel. The resultant cellulose-aerogel composites exhibit thermal conductivity of 34.68 mW m-1 K-1, mechanical flexibility with a flexural modulus of 429.21 MPa, and superhydrophobicity with water contact angle of 158.72°. Moreover, we present the additive manufacturing process of recycled cellulose aerogel composites, providing enormous potential for high energy efficiency and carbon-sequestration building applications.

Transparent thermal insulation ceramic aerogel materials for solar thermal conversion.

Thermal management in energy-efficient solar thermal energy conversion and transparent windows requires advanced materials with low thermal conductivity and high transparency, such as transparent silica aerogel materials. However, the large scatter domains in porous silica materials would deteriorate their optical transparency. Herein, we report transparent silica aerogels by controlling hydrolyzation and meanwhile silylation modification to enhance the integrity of the microstructure under ambient pressure drying. The transparent silica aerogel materials show a broad-spectrum transparency of 70% from 400 nm and 800 nm, showing promising applications in transparent windows and solar thermal energy conversion systems. The scalability for transparent windows could be achieved with a composite material by incorporating transparent polymeric materials. The solar receiver coupled with a transparent silica aerogel could reach 122 °C within 12 min at a solar irradiance of 1 Sun, ∼200% higher than that in the ambient atmosphere. The engineered structure of the transparent porous silica backbone provides a pathway for solar thermal systems and transparent window applications.

Manufacturing silica aerogel and cryogel through ambient pressure and freeze drying.

Achieving a mesoporous structure in superinsulation materials is pivotal for guaranteeing a harmonious relationship between low thermal conductivity, high porosity, and low density. Herein, we report silica-based cryogel and aerogel materials by implementing freeze-drying and ambient-pressure-drying processes respectively. The obtained freeze-dried cryogels yield thermal conductivity of 23 mW m-1 K-1, with specific surface area of 369.4 m2 g-1, and porosity of 96.7%, whereas ambient-pressure-dried aerogels exhibit thermal conductivity of 23.6 mW m-1 K-1, specific surface area of 473.8 m2 g-1, and porosity of 97.4%. In addition, the fiber-reinforced nanocomposites obtained via freeze-drying feature a low thermal conductivity (28.0 mW m-1 K-1) and high mechanical properties (∼620 kPa maximum compressive stress and Young's modulus of 715 kPa), coupled with advanced flame-retardant capabilities, while the composite materials from the ambient pressure drying process have thermal conductivity of 28.8 mW m-1 K-1, ∼200 kPa maximum compressive stress and Young's modulus of 612 kPa respectively. The aforementioned results highlight the capabilities of both drying processes for the development of thermal insulation materials for energy-efficient applications.

Printing Air-Stable High-Tc Molecular Magnet with Tunable Magnetic Interaction.

High-Tc molecular magnets have amassed much promise; however, the long-standing obstacle for its practical applications is the inaccessibility of high-temperature molecular magnets showing dynamic and nonvolatile magnetization control. In addition, its functional durability is prone to degradation in oxygen and heat. Here, we introduce a rapid prototyping and stabilizing strategy for high Tc (360 K) molecular magnets with precise spatial control in geometry. The printed molecular magnets are thermally stable up to 400 K and air-stable for over 300 days, a significant improvement in its lifetime and durability. X-ray magnetic circular dichroism and computational modeling reveal the water ligands controlling magnetic exchange interaction of molecular magnets. The molecular magnets also show dynamical and reversible tunability of magnetic exchange interactions, enabling a colossal working temperature window of 86 K (from 258 to 344 K). This study provides a pathway to flexible, lightweight, and durable molecular magnetic devices through additive manufacturing.

Laser-Induced Cooperative Transition in Molecular Electronic Crystal.

The competing and non-equilibrium phase transitions, involving dynamic tunability of cooperative electronic and magnetic states in strongly correlated materials, show great promise in quantum sensing and information technology. To date, the stabilization of transient states is still in the preliminary stage, particularly with respect to molecular electronic solids. Here, a dynamic and cooperative phase in potassium-7,7,8,8-tetracyanoquinodimethane (K-TCNQ) with the control of pulsed electromagnetic excitation is demonstrated. Simultaneous dynamic and coherent lattice perturbation with 8 ns pulsed laser (532 nm, 15 MW cm-2 , 10 Hz) in such a molecular electronic crystal initiates a stable long-lived (over 400 days) conducting paramagnetic state (≈42 Ωcm), showing the charge-spin bistability over a broad temperature range from 2 to 360 K. Comprehensive noise spectroscopy, in situ high-pressure measurements, electron spin resonance (ESR), theoretical model, and scanning tunneling microscopy/spectroscopy (STM/STS) studies provide further evidence that such a transition is cooperative, requiring a dedicated charge-spin-lattice decoupling to activate and subsequently stabilize nonequilibrium phase. The cooperativity triggered by ultrahigh-strain-rate (above 106 s- 1 ) pulsed excitation offers a collective control toward the generation and stabilization of strongly correlated electronic and magnetic orders in molecular electronic solids and offers unique electro-magnetic phases with technological promises.

Hierarchical Structural Engineering of Ultrahigh-Molecular-Weight Polyethylene.

Nature has inspired the design of next-generation lightweight architectured structural materials, for example, nacre-bearing extreme impact and paw-pad absorbing energy. Here, a bioinspired functional gradient structure, consisting of an impact-resistant hard layer and an energy-absorbing ductile layer, is applied to additively manufacture ultrahigh-molecular-weight polyethylene (UHMWPE). Its crystalline graded and directionally solidified structure enables superior impact resistance. In addition, we demonstrate nonequilibrium processing, ultrahigh strain rate pulsed laser shock wave peening, which could trigger surface hardening for enhanced crystallinity and polymer phase transformation. Moreover, we demonstrate the paw-pad-inspired soft- and hard-fiber-reinforced composite structure to absorb the impact energy. The bioinspired design and nonequilibrium processing of graded UHMWPE shed light on lightweight engineering polymer materials for impact-resistant and threat-protection applications.

An All-Ceramic, Anisotropic, and Flexible Aerogel Insulation Material.

To exploit the high-temperature superinsulation potential of anisotropic thermal management materials, the incorporation of ceramic aerogel into the aligned structural networks is indispensable. However, the long-standing obstacle to exploring ultralight superinsulation ceramic aerogels is the inaccessibility of its mechanical elasticity, stability, and anisotropic thermal insulation. In this study, we report a recoverable, flexible ceramic fiber-aerogel composite with anisotropic lamellar structure, where the interfacial cross-linking between ceramic fiber and aerogel is important in its superinsulation performance. The resulting ultralight aerogel composite exhibits a density of 0.05 g/cm3, large strain recovery (over 50%), and low thermal conductivity (0.0224 W m-1 K-1), while its hydrophobicity is achieved by in situ trichlorosilane coating with the water contact angle of 135°. The hygroscopic tests of such aerogel composites demonstrate a reversible thermal insulation. The mechanical elasticity and stability of the anisotropic composites, with its soundproof performance, shed light on the low-cost superelastic aerogel manufacturing with scalability for energy saving building applications.

Correlation at two-dimensional charge-transfer FeSe interface.

The charge transfer and spin coupling effects are explored at the interface of two-dimensional (2D) superconducting FeSe nanosheets and molecular photochromic potassium-7,7,8,8-tetracyanoquinodimethane (KTCNQ). Light-induced conductivity in 2D FeSe nanosheets is enhanced by the electron doping from KTCNQ by the destabilized spin-Peierls phase through their interface. Furthermore, the spin coupling at the interface of FeSe and KTCNQ shifts the dimerization transition temperature of KTCNQ. Our results suggest 2D exfoliated FeSe nanosheets as a versatile strongly correlated platform for the study of interfacial electron doping and spin coupling.

Strongly Correlated Aromatic Molecular Conductor.

Strongly correlated electronic molecules open the way for strong coupling between charge, spin, and lattice degrees of freedom to enable interdisciplinary fields, such as molecular electronic switches and plasmonics, spintronics, information storage, and superconducting circuits. However, despite exciting computational predictions and promising advantages to prepare flexible geometries, the electron correlation effect in molecules has been elusive. Here, the electron correlation effects of molecular plasmonic films are reported to uncover their coupling of charge, spin, lattice, and orbital for the switchable metal-to-insulator transition under external stimuli, at which the simultaneous transition occurs from the paramagnetic, electrical, and thermal conducting state to the diamagnetic, electrical, and thermal insulating state. In addition, density functional theory calculation and spectroscopic studies are combined to provide the mechanistic understanding of electronic transitions and molecular plasmon resonance observed in molecular conducting films. The self-assembled molecular correlated conductor paves the way for the next generation integrated micro/nanosystems.

Alkali-Metal-Intercalated Percolation Network Regulates Self-Assembled Electronic Aromatic Molecules.

In the continuously growing field of correlated electronic molecular crystals, there is significant interest in addressing alkali-metal-intercalated aromatic hydrocarbons, in which the possibility of high-temperature superconductivity emerges. However, searching for superconducting aromatic molecular crystals remains elusive due to their small shielding fraction volume. To exploit this potential, a design principle for percolation networks of technologically important film geometry is indispensable. Here the effect of potassium-intercalation is shown on the percolation network in self-assembled aromatic molecular crystals. It is demonstrated that one-dimensional (1D) dipole pairs, induced by dipole interaction, regulate the conductivity, as well as the electronic and optical transitions, in alkali-metal-intercalated molecular electronic crystals. A solid-solution growth methodology of aromatic molecular films with a broad range of stability is developed to uncover electronic and optical transitions of technological importance. The light-induced electron interactions enhance the charge-carrier itinerancy, leading to a switchable metal-to-insulator transition. This discovery opens a route for the development of aromatic molecular electronic solids and long-term modulation of electronic efficacy in nanotechnologically important thin films.