We present the results of a combined experimental and theoretical investigation of the mechanics of self-burial of some plant seeds whose morphologies respond to environmental changes in humidity. The seeds of Erodium and Pelargonium have hygroscopically responsive awns that play a critical role in their self-burial into soil. The awn, coiled in a dry state, uncoils to stretch linearly under highly humid condition because of a tilted arrangement of cellulose microfibrils in one of the layers of the awn's bilayered structure. By measuring the mechanical characteristics of the awns of Pelargonium carnosum, we find that the extensional force of the awn can be aptly modeled by the theory of elasticity for a coiled spring. We further show that although the resistance to the seed-head penetrating relatively coarse soils without spinning is large enough to block the digging seed, the rotation of the seed greatly reduces the soil's resistance down to a level the awn can easily overcome. Our mechanical analysis reveals that the self-burial of the seed is a sophisticated outcome of the helically coiled configuration of the awn.
We report a method to create a self‐cleaning, transparent surface on poly(methyl methacrylate) (PMMA) using a dry etching with CF4 plasma and a subsequent hydrolysis process with water immersion. During the CF4 plasma treatment, nanoscale pillar structures were formed and its aspect ratio tended to increase. However, the transparency was reduced due to the deposition and the accumulation of undesired capping layers, which cover the structures. The hydrolysis was used to remove the capping layers of metal fluoride. As a result, the surface improves their clarity based on the transmittance up to 95%, because the reflectivity was reduced. With a subsequent hydrophobic coating, a superhydrophobic surface was achieved showing robust anti‐wetting and anti‐dewing effects.
A circular reactor was placed outdoors to investigate the possibility of using natural sunlight in TiO2 photocatalysis system for the removal of toxic metals (Cd, Cr, Cu, Hg, Ni, Zn) and EDTA complex. The results show that the system containing both solar light and TiO2 more effectively removed metal-EDTA complex than either solar light or TiO2 system alone. The removal of each metal was more than 90% in the presence of TiO2/solar light, and EDTA (TOC basis) was reduced more than 80% in 120 min. Photocatalytic removal efficiency of heavy metal-EDTA increased with increasing TiO2 dosage. However, over 1.5g/L of TiO2 dosage, the efficiency reached a plateau.
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