developing multifunctional surfaces with unique capabilities, including superhydrophobicity, [1,2] self-cleaning, [3,4] anti-icing, [3,5] anti-biofoulin, [6,7] biological sensors, [6] and radiative cooling. [6,8] For example, Namib Desert beetles use the superhydrophobicsuperhydrophilic micropatterned skin to harvest water from fog. [12][13][14] Plants such as lotus utilize microstructures on leaves to influence wetting behavior and enable self-cleaning. [12,15] Sharks' unique skin morphology augments the near-wall vorticity during turbulent flow. This augmentation reduces the skin friction and enables sharks to be one of the most efficient swimming species in the ocean. [16][17][18] These dragreducing microstructures are particularly interesting to the scientific community. Thus, researchers have focused on periodic microstructures aligned in the flow direction, similar to sharkskin. [19] In prior modeling and experimentation, researchers have decreased frictional drag by using different variations of linear periodic microstructures. For example, Xu et al. developed a series of linear microtrenches demonstrating a maximum drag reduction of ≈30% in high Reynolds number applications. [20] In addition, Park et al. studied the impact of grating parameters on drag reduction and demonstrated a max drag reduction of 75%. [21] Lithography is one of the standard processes for manufacturing superhydrophobic periodic microstructures. [20][21][22] Periodic micro/nanoscale structures from nature have inspired the scientific community to adopt surface design for various applications, including superhydrophobic drag reduction. One primary concern of practical applications of such periodic microstructures remains the scalability of conventional microfabrication technologies. This study demonstrates a simple template-free scalable manufacturing technique to fabricate periodic microstructures by controlling the ribbing defects in the forward roll coating. Viscoelastic composite coating materials are designed for roll-coating using carbon nanotubes (CNT) and polydimethylsiloxane (PDMS), which helps achieve a controllable ribbing with a periodicity of 114-700 µm. Depending on the process parameters, the patterned microstructures transition from the linear alignment to a random structure. The periodic microstructure enables hydrophobicity as the water contact angles of the samples ranged from 128° to 158°. When towed in a static water pool, a model boat coated with the microstructure film shows 7%-8% faster speed than the boat with a flat PDMS film. The CNT addition shows both mechanical and electrical properties improvement. In a mechanical scratch test, the cohesive failure of the CNT-PDMS film occurs in ≈90% higher force than bare PDMS. Moreover, the nonconductive bare PDMS shows sheet resistance of 747.84-22.66 Ω □ −1 with 0.5 to 2.5 wt% CNT inclusion.

The construction and evaluation of wholly skutterudite thermoelectric modules with a high volume-power-density is described. Such modules afford the maximum power output for the minimum use of material. Synthesis of the component ntype unfilled skutterudite CoSb 2.75 Sn 0.05 Te 0.20 and p-type filled skutterudite Ce 0.5 Yb 0.5 Fe 3.25 Co 0.75 Sb 12 was achieved using a scalable ball-milling route that provides sufficient material for the construction and assessment of performance of 12 modules. Impedance spectroscopy at room temperature is shown to provide a rapid means of evaluating the quality of module fabrication. The results show a high degree of reproducibility in module performance across the 12 modules, with an average internal resistance of 102(4) mΩ. Electrical measurements on the component n-and p-type materials reveal power factors (S 2 /ρ) of 1.92 and 1.33 mW m −1 K −2 , respectively, at room temperature and maximum figures of merit of ZT = 1.13 (n-type) and ZT = 0.91 (p-type) at 673 and 823 K, respectively. The figure of merit of the module at room temperature (ZT = 0.12) is reduced by ca. 39% from the average of the n-and p-type component materials at the same temperature, as a result of thermal-and electrical-contact resistance losses associated with the architecture of the module. I−V curves for the module determined for ΔT in the range 50−450 K show an almost linear dependence of the open-circuit voltage on ΔT and allow calculation of the power output, which reaches a maximum value of 1.8 W (0.9 W cm −2 ) at ΔT = 448 K.

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