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Nanophotonics relies on precise control of refractive index (RI) which can be designed with metamaterials. Plasmonic superstructures of nanoparticles (NPs) can suggest a versatile way of tuning RI. However, the plasmonic effects in the superstructures demand 1 nm‐level exquisite control over the interparticle gap, which is challenging in a sub‐wavelength NPs. Thus far, a large‐area demonstration has been mostly discouraged. Here, heteroligand AuNPs are prepared, which are stable in oil but become Janus particles at the oil–water interface, called “adaptive Janus particles.” NPs are bound at the interface and assembled into 2D arrays over square centimeters as toluene evaporates, which distinctively exhibits the RI tunability. In visible and NIR light, the 2D superstructures exhibit the highest‐ever RI (≈7.8) with varying the size and interparticle gap of NPs, which is successfully explained by a plasmonic percolation model. Furthermore, fully solution‐processable 2D plasmonic superstructures are proved to be advantageous in flexible photonic devices such as distributed Bragg reflectors.

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The addition of small amounts of carbon nanotubes (CNTs) to cement-based materials modifies their thermal and electrical characteristics. This study investigated the void detection and filling rates of cement grout with multi-walled carbon nanotubes (MWCNTs). MWCNT grouts of 40 mm × 40 mm × 160 mm were fabricated. Specimens were tested by thermal imaging, electrical resistance analyses, and magnetic field tests. The experimental parameters were the concentration of MWCNT and the grout filling rate. The filling rate was investigated by measuring resistance and magnetic field changes with respect to cross-sectional area, taking the voids into consideration. The results of the thermal image tests indicate that 1.0 wt % MWCNT cement grout is optimal for void detection.