Thermal transport in layered, two-dimensional (2D) black phosphorus (BP) is of great interest, not only due to its importance in the designs of BP devices, [1] but also because it provides a unique platform to study the physics of heat transport in highly anisotropic materials. [2] BP belongs to the orthorhombic Cmca point group, [3] with its puckered honeycomb basal planes weakly bonded together by interlayer van der Waals'forces. Due to the nature of its crystal structure, second order tensors (e.g., the thermal conductivity tensor Λ) of BP have three independent components along the principal axes of zigzag (ZZ), armchair (AC) and through-plane (TP), see Figure 1a, and the thermal conductivity tensor is strongly anisotropic along these axes. [4] (In this paper, we use ΛZZ, ΛAC and ΛTP to denote the three independent components of the thermal conductivity tensor.) Here, we accurately measured and report the anisotropic thermal conductivity tensor (ΛZZ, ΛAC and ΛTP) of bulk BP in a temperature range of 80 ≤ T ≤ 300 K. Our temperature dependence measurements provide a crucial benchmark for future studies of anisotropic heat transport in BP and phosphorene.To date, there are only few experimental works on anisotropic thermal conductivity of BP, even at 300 K. Luo et al. [5] and Lee et al. [6] measured BP flakes with a thickness of 9 -30 nm and 60 -310 nm using the opto-thermal Raman method and the micro-bridge technique, respectively, and reported ΛZZ = 11 -45 W m -1 K -1 and ΛAC = 5 -22 W m -1 K -1 at room temperature. These values of ΛZZ and ΛAC are substantially lower than predictions by first-principles calculations [4, 7, 8] for bulk BP and phosphorene. While these low values of thermal conductivity were attributed to additional boundary scattering of phonons in the thin flakes, [5, 6] we note that scattering of phonons along the basal planes by the interfaces is rather weak [9] and thus this explanation might not be satisfactory. The low values could also originate from degradation of the BP flakes by oxidation, [10] as the BP flakes in both studies were exposed to the air for a substantial amount of time during sample preparation and measurements. With the degradation, the reported thermal conductivity is probably not intrinsic. Jang et al. [11] encapsulated their BP flakes of thickness of 138 -552 nm with a 3- Zhu et al.'s samples were not seriously oxidized, their pump-probe measurements in the through-plane direction might be lower than the intrinsic ΛTP because the mean-free-paths () of a substantial portion of heat-carrying phonons are much longer than the characteristic length scales of their measurements (<500 nm), i.e., the thickness of the samples or the thermal penetration depth d. [12][13][14] In fact, we obtained a ΛTP value ~25 % higher than Jang et al. 's and Zhu et al.'s measurements, [4, 11] when we used a much lower modulation frequency in our measurements to achieve a larger thermal penetration depth.With the relatively few published works on the thermal properties of BP, kn...

Poly(vinyl alcohol) (PVA) hydrogels with tissue-like viscoelasticity, excellent biocompatibility, and high hydrophilicity have been considered as promising cartilage replacement materials. However, lack of sufficient mechanical properties is a critical barrier to their use as load-bearing cartilage substitutes. Herein, we report hydroxylated boron nitride nanosheets (OH-BNNS)/PVA interpenetrating hydrogels by cyclically freezing/thawing the aqueous mixture of PVA and highly hydrophilic OH-BNNS (up to 0.6 mg/mL, two times the highest reported so far). Encouragingly, the resulting OH-BNNS/PVA hydrogels exhibit controllable reinforcements in both mechanical and thermal responses by simply varying the OH-BNNS contents. Impressive 45, 43, and 63% increases in compressive, tensile strengths and Young's modulus, respectively, can be obtained even with only 0.12 wt% (OH-BNNS:PVA) OH-BNNS addition. Meanwhile, exciting improvements in the thermal diffusivity (15%) and conductivity (5%) can also be successfully achieved. These enhancements are attributed to the synergistic effect of intrinsic superior properties of the as-prepared OH-BNNS and strong hydrogen bonding interactions between the OH-BNNS and PVA chains. In addition, excellent cytocompatibility of the composite hydrogels was verified by cell proliferation and live/dead viability assays. These biocompatible OH-BNNS/PVA hydrogels are promising in addressing the mechanical failure and locally overheating issues as cartilage substitutes and may also have broad utility for biomedical applications, such as drug delivery, tissue engineering, biosensors, and actuators.

Branched MnOOH nanorods with diameters in the range of 50-150 nm and lengths of up to tens of micrometers were prepared by using potassium permanganate (KMnO(4)) and PEG 400 (PEG=polyethylene glycol) as starting materials through a simple hydrothermal process at 160 °C. After annealing at 300 °C under a N(2) atmosphere for 5 h, MnOOH nanorods became gradually dehydrated and transformed into mesoporous Mn(3)O(4) nanorods with a slight size-shrinking. The as-obtained mesoporous Mn(3)O(4) nanorods had an average surface area of 32.88 m(2) g(-1) and a mean pore size of 3.7 nm. Through tuning the experimental parameters, such as the annealing atmosphere and temperature, β-MnO(2), Mn(2)O(3), Mn(3)O(4), MnO, and Mn(5)O(8) were selectively produced. Among these structures, mesoporous Mn(3)O(4) nanorods were efficient for the catalytic degradation of methylene blue (MB) in the presence of H(2)O(2) at 80 °C.

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Thermal radiation from a black body increases with the fourth power of absolute temperature (T4), an effect known as the Stefan–Boltzmann law. Typical materials radiate heat at a portion of this limit, where the portion, called integrated emissivity (εint), is insensitive to temperature (|dεint/dT| ≈ 10−4 °C–1). The resultant radiance bound by the T4 law limits the ability to regulate radiative heat. Here, an unusual material platform is shown in which εint can be engineered to decrease in an arbitrary manner near room temperature (|dεint/dT| ≈ 8 × 10−3 °C–1), enabling unprecedented manipulation of infrared radiation. As an example, εint is programmed to vary with temperature as the inverse of T4, precisely counteracting the T4 dependence; hence, thermal radiance from the surface becomes temperature‐independent, allowing the fabrication of flexible and power‐free infrared camouflage with unique advantage in performance stability. The structure is based on thin films of tungsten‐doped vanadium dioxide where the tungsten fraction is judiciously graded across a thickness less than the skin depth of electromagnetic screening.