Maintaining constant body temperature is the most basic function of textiles. However, traditional fabrics irradiate a massive amount of thermal energy to the ambient environment due to the high emissivity of the materials used for textiles. This phenomenon weakens the thermal function, causing vast thermal energy loss by dissipation as infrared (IR) irradiation. To improve thermal comfort and reduce extra energy consumption, smart thermal management textiles must maintain constant body temperature by regulating IR irradiation from the human body or by compensating heat losses by joule heating. Here, a smart dual‐sided nonwovens’ preparation procedure and properties for use as a textile with this combination of properties are shown. The nonwoven combines a high porosity with high IR reflectance and low IR emittance. The nonwoven is adjustable from reflective to emissive when turned inside out. It is consequently permeable to air and vapor and simultaneously mitigates thermal heat losses with radiation. In addition, low sheet resistance and superior flexibility make it possible to use them in flexible electronics and wearable devices. It can be further equipped with a porous Joule heating layer adding active control to the personal thermal comfort.

Microscopic electric fields govern the majority of elementary excitations in condensed matter and drive electronics at frequencies approaching the Terahertz (THz) regime. However, only few imaging schemes are able to resolve sub-wavelength fields in the THz range, such as scanning-probe techniques, electro-optic sampling, and ultrafast electron microscopy. Still, intrinsic constraints on sample geometry, acquisition speed and field strength limit their applicability. Here, we harness the quantum-confined Stark-effect to encode ultrafast electric near-fields into colloidal quantum dot luminescence. Our approach, termed Quantum-probe Field Microscopy (QFIM), combines far-field imaging of visible photons with phase-resolved sampling of electric waveforms. By capturing ultrafast movies, we spatio-temporally resolve a Terahertz resonance inside a bowtie antenna and unveil the propagation of a Terahertz waveguide excitation deeply in the sub-wavelength regime. The demonstrated QFIM approach is compatible with strong-field excitation and sub-micrometer resolution—introducing a direct route towards ultrafast field imaging of complex nanodevices in-operando.

The field of passive daytime radiative cooling materials has significantly developed in the last decade. Many new materials emerged that show a cooling effect below ambient temperature, even with direct sunlight illumination. [1] The key to achieving a net cooling power is minimizing energy absorption and maximizing energy emission. A multitude of approaches were proposed that lead to the desired optical properties, including photonic structures, [2] polymeric materials, [3] and composite materials. [4] A material is primarily a good candidate for passive radiative cooling if it exhibits a high emissivity in the wavelength range of thermal radiation at ambient temperature. This wavelength range is located in the mid to far infrared (IR) region (%3-50 μm). Second, a low absorptivity in the solar region is required because any energy uptake from the sun directly reduces the cooling power. This energy absorption is prevented by including a reflective metal layer below the emitter material, [4b,5] using a solar filter approach, [6] or by efficient scattering of solar wavelengths by the material itself. [3a,7] Third and most complex is to avoid radiative energy uptake by the surrounding atmosphere. As this radiance appears in a similar wavelength regime as the emitted thermal radiation, special care must be taken. The most common approach here is to focus emission on the first (8-13 μm) and second (16-28 μm) atmospheric transmission window where low atmospheric radiation is present. With a confined emission in this spectral region, the lowest temperatures below ambient can be reached. However, the cooling power at ambient temperature is reduced in comparison to a blackbody emitter. [1a,8] The material thickness is an essential parameter for the applicability of passive cooling materials and was discussed by several groups in the literature. [5b,9] For example, in the work of Zhou et al., a PDMS layer on an aluminum substrate is considered. [5b] The authors chose a 150 μm-thick layer and found that above 100 μm thickness, the emissivity in the 8-13 μm wavelength range was close to unity. In the work of Zhu et al., the thickness of a PDMS layer on a reflective silver layer was discussed, and a thickness of 200 μm was suggested. [9b] The authors found that up to this thickness, the emissivity in the wavelength range from 2.5 to 25 μm was increasing, but for a higher thickness of 300 μm, there were only minor changes. Besides PDMS as emitting layer, the group of Zhu et al. investigated the thickness of a composite material consisting of In 2 O 3 particles in a polymethyl methacrylate matrix. [10] They found the thickness of their composite needs to be larger than 25 μm to have high emissivity within the

Efficient thermal insulation at high temperatures poses stringent requirements on suitable materials. Low density, porous inorganic structures with pore sizes in the sub‐micrometer range are of particular interest for such materials to control heat conduction. Simultaneously, thermal radiation has to be suppressed, which depends on the optical properties of the constituents. Here, the authors demonstrate a direct observation of the transition from a conduction dominated to a radiation dominated thermal transport mechanism for the case of particulate silica materials at temperatures reaching up to 925 °C. A detailed analysis of the radiative transport through bulk silica as well as solid and hollow silica particles is provided. Optical transparency at high temperatures is the driving force, whereas surface wave modes barely contribute, particularly in case of the insulating particle packings. The existing analytical framework of laser flash analysis is extended to qualitatively describe the radiative and conductive heat transport by two independent diffusive transport models. The analysis provides a better understanding of the challenges to fabricate and analyze efficient thermal insulation materials at high operating temperatures, where multiple heat transport mechanisms need to be controlled.

No abstract