Freshwater scarcity has become a severe global crisis, and sorption-based atmospheric water harvesting (SAWH) is a promising solution. Traditional lithium chloride-based hygroscopic hydrogels suffer from sluggish adsorption-desorption kinetics caused by disordered pore channels and insufficient internal mass transfer. In this work, a photothermal hygroscopic hydrogel (DFHG-Li) with vertically aligned directional channels is synthesized through directional freezing-assisted polymerization. Directed ice templates create unobstructed mass transfer tunnels, graphene oxide endows excellent solar-to-thermal conversion performance, and evenly anchored LiCl offers abundant water capture sites. Characterizations confirm complete pore integrity and uniform salt distribution. Optimized DFHG-Li reaches swelling equilibrium in merely 3 min and delivers a high water uptake of 3.37 g g^-1 at 90% RH. Under 1 sun irradiation, its surface temperature rises to 51.2 °C within 15 min, achieving a desorption efficiency of 91.5% in 70 min. After 20 adsorption-desorption cycles, over 89% of its initial water absorption capacity is maintained. This work provides an effective structural regulation strategy to boost mass transfer for high-efficiency solar-driven atmospheric water harvesting.

Cubic boron arsenide (BAs) is a promising filler for polymer-based thermal interface materials owing to its ultrahigh intrinsic thermal conductivity and electrically insulating nature. However, the interfacial thermal conductance (ITC) between BAs and polymer matrices has not been systematically quantified. Heat transport across BAs/epoxy interfaces was investigated by molecular dynamics simulations for five low-index surface terminations, and the calculated ITC varies by a factor of 1.72 among them. B-terminated interfaces systematically exhibit higher ITC than their As-terminated counterparts. The molecular functionalization of the surface shows that aminopropoxy functionalization at 16% coverage increases the ITC to 277 MW m^-2 K^-1, nearly twice that of the pristine B-terminated interface. Spectral analysis indicates that surface-bound functional groups act as vibrational bridges between BAs and epoxy, while covalent cross-linking with the epoxy network further strengthens the existing interfacial heat-transfer channels. The area-normalized interfacial coupling stiffness reveals that the termination dependence of ITC is governed by the strength of the cross-interface vibrational coupling. This work provides systematic quantitative data for BAs/polymer interfaces and shows that surface termination control and covalent functionalization can be combined to improve interfacial thermal conductance.

At cryogenic temperatures, thermal transport is predominantly governed by long-wavelength acoustic phonons with exceptionally long intrinsic mean free paths, leading to significant departures from the diffusive transport behavior characteristic of room temperature. Understanding these transport mechanisms is essential for emerging technologies, including quantum computing, cryogenic electronics, and aerospace systems. This review summarizes the fundamental physics governing phonon-mediated thermal transport in the cryogenic regime. We first introduce the classical Casimir-Knudsen framework for geometry-limited transport and then discuss how this picture is modified by reduced dimensionality, competing scattering mechanisms, collective phonon transport, and wave effects. Particular emphasis is placed on the physical origins of thermal-conductivity behaviors that deviate from the conventional T³ scaling. We further examine the implications of cryogenic phonon transport for self-heating and thermal management in electronic and quantum devices. Finally, we identify key unresolved questions, particularly regarding predictive modeling and thermal management in cryogenic quantum devices. By providing a unified overview of recent advances, this review aims to stimulate further progress in the fundamental understanding and engineering of thermal transport at cryogenic temperatures.

Cu₂SnSe₃ exhibits exceptionally low lattice thermal conductivity (κ_L) and a nonclassical temperature dependence among ternary copper-based diamondoid compounds, yet the microscopic origins of these phonon behaviors remain poorly understood. In this work, we theoretically investigate the intrinsic phonon transport in Cu₂SnSe₃ by employing a two-channel thermal transport model that separates particle-like (κ_p) and coherent contributions (κ_c), while fully incorporating both three-phonon (3ph) and four-phonon (4ph) scattering processes. Our calculations show that κ_c is negligible at 300 K but becomes progressively more significant at elevated temperatures, while κ_p remains the dominant contributor to κ_L over the entire temperature range. 4ph scattering is identified as the primary factor driving the deviation from the classical T^-1 dependence, yielding a temperature scaling of T^-1.1 that closely matches the experimental T^-1.2 behavior. This strong 4ph scattering originates from flat optical phonon modes in the 1.2-2.2 THz range, which provide an exceptionally large scattering phase space. The low κ_L (e.g., ~ 0.8 W m^-1 K^-1 at 773 K) of Cu₂SnSe₃ relative to other ternary copper-based diamondoid compounds is attributed to the asymmetric potential energy of Cu atoms, which induces large atomic displacement parameters and pronounced anharmonicity in the Cu-related low-frequency optical branches. Furthermore, qualitative analyses of cation disorder and anion substitution show that disorder leads to significant phonon broadening, while replacing Se with S hardens the acoustic branches and markedly shifts the optical modes upward. Our findings not only clarify the origins of the nonclassical temperature dependence and low κ_L in Cu₂SnSe₃, but also provide a general guideline for designing diamondoid thermoelectrics with intrinsically suppressed κ_L.