Daytime radiative cooling presents an exciting new strategy for combating global warming, because it can passively cool buildings by reflecting sunlight and utilizing the infrared atmospheric window to eject heat into outer space. Recent progress with novel material designs showed promising subambient cooling performance under direct sunlight. However, large-scale implementation of radiative cooling technologies is still limited by the high-cost and complex fabrication. Here, we develop a nanoporous polymer matrix composite (PMC) to enable rapid production and cost reduction using commercially available polymer processing techniques, such as molding, extrusion, and 3D printing. With a high solar reflectance of 96.2% and infrared emissivity > 90%, the nanoporous PMC achieved a subambient temperature drop of 6.1 °C and cooling power of 85 W/m 2 under direct sunlight, which are comparable to the state-of-the-art. This work offers great promise to make radiative cooling technologies more viable for saving energy and reducing emissions in building cooling applications.

No abstract

No abstract

Bottlebrush polymers are a class of semiflexible, hierarchical macromolecules with unique potential for shape-, architecture-, and composition-based structure–property design. It is now well-established that in dilute to semidilute solution, bottlebrush homopolymers adopt a wormlike conformation, which decreases in extension (persistence length) as the concentration and molecular overlap increase. By comparison, the solution phase self-assembly of bottlebrush diblock copolymers (BBCP) in a good solvent remains poorly understood, despite critical relevance for solution processing of ordered phases and photonic crystals. In this work, we combine small-angle X-ray scattering, coarse-grained simulation, and polymer synthesis to map the equilibrium phase behavior and conformation of a set of large, nearly symmetric PS-b-PLA bottlebrush diblock copolymers in toluene. Three BBCP are synthesized, with side chains of number-averaged molecular weights of 4500 (PS) and 4200 g/mol (PLA) and total backbone degrees of polymerization of 100, 255, and 400 repeat units. The grafting density is one side chain per backbone repeat unit. With increasing concentration in solution, all three polymers progress through a similar structural transition: from dispersed, wormlike chains with concentration-dependent (decreasing) extension, through the onset of disordered PS/PLA compositional fluctuations, to the formation of a long-range ordered lamellar phase. With increasing concentration in the microphase-separated regimes, the domain spacing increases as individual chains partially re-extend due to block immiscibility. Increases in the backbone degree of polymerization lead to changes in the scattering profiles which are consistent with the increased segregation strength. Coarse-grained simulations using an implicit side-chain model are performed, and concentration-dependent self-assembly behavior is qualitatively matched to experiments. Finally, using the polymer with the largest backbone length, we demonstrate that lamellar phases develop a well-defined photonic band gap in solution, which can be tuned across the visible spectrum by varying polymer concentration.

This article describes the design and implementation of a monolithic 24/60‐GHz dual‐band millimeter‐ wave planar CMOS antenna.A finite element method‐based 3D full‐wave electromagnetic solver, high‐frequency structure simulator, is used to simulate and optimize the performance of the antenna. The feeding network adopts the coplanar waveguide (CPW) structure, so the on‐chip antenna can be flip‐chip‐bonded to a CPW RO4003 conversion board for complete radiation‐pattern measurement. The main structure uses meander‐line to save chip area. Dual‐band operation is achieved by providing two major current paths for radiation. The measured input voltage standing wave ratio of the on‐chip dual‐band antenna is smaller than 2 for frequencies 10–25.7 and 58.4–66.6 GHz. The measured maximum power gain is −7 dB at 60 GHz, one of the highest power gains ever reported for a CMOS antenna at 60 GHz. The chip area is only 1 × 0.75 mm2, i.e., 0.75 mm2, excluding the periphery conductor and the dummy metals for metal density requirement. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1731–1737, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26916

No abstract

Additive manufacturing (AM, 3D Printing) of hierarchical polymer structures for a targeted function represents a grand challenge in the field of polymer science and engineering. Because advanced functional materials often do not possess suitable mechanical and rheological properties for conventional fused deposition modeling, a key challenge that researchers face is in integrating custom deposition tool heads that enable printing of non-filamentary materials while preserving synchrony with the motion axes. In this article, we demonstrate a highly versatile hardware and software platform for melt and solutionphase benchtop AM and highlight patterning and post-deposition processing of

A monopole antenna embedded in low temperature cofired ceramic (LTCC) for end-fire radiation is presented in this paper. It provides horizontal polarization at 60 GHz band for short range high speed data communication. The antenna is embedded at edge of an LTCC substrate for end-fire radiation. The size of the antenna without feeding structure is 2.5mm(W) X 1.0mm(D) X 1.38mm(H) and embedded in a substrate of 2.8mm(W) X 2.44mm(D) X 1.38mm(H). The measured -10dB input matching bandwidth is 62~65GHz. Simulation results show about 4.7dB gain and 3dB beamwidth of 85 degree and 125 degree at horizontal and vertical plane.