Abstract Synthetic routes for LiCoO 2 mesocrystals with porous and single‐crystalline structures through the topotactic transformation of precursor crystals are developed. Octahedral LiCoO 2 frameworks of 4–6 μm in diameter, consisting of 600–800 nm subunits, are obtained from octahedral solid particles of Co 2 (OH) 3 Cl. Hollow LiCoO 2 plates about 600 nm wide and 40 nm thick composed of 100–400 nm subunits are produced from hexagonal disks of β‐Co(OH) 2 . The LiCoO 2 mesocrystals exhibit enhanced charge–discharge cycle stability and rate performance as a cathode material for lithium‐ion batteries. The high reactive surface area, owing to the porous framework, and high lithium‐ion and electron conductivities, originating from the single‐crystalline nature, effectively enhance their electrochemical properties.
Abstract Fluorine-free superhydrophobic surfaces have been required to meet environmental regulations in recent years. A new nanoarchitectonics is required to achieve superhydrophobicity without using perfluoroalkyl compounds. In the present work, surface-modified exfoliated nanosheets with polydispersed sizes were utilized to prepare coatings with high surface roughness and low surface energy. Fluorine-free superhydrophobic surfaces were obtained by spray coating of surface-modified exfoliated nanosheets based on transition-metal oxides. The water contact angle (θw) 166.0 ± 0.5° is the highest compared with that of the fluorine-free substrate-independent coatings in previous reports. The significant factors related to θw were studied using machine learning combined with our chemical insight in the small data obtained in the present work. The resultant superhydrophobic coatings exhibited unique properties, such as sliding of water droplets, superoleophilic behavior, recyclability, and durability. The present design strategy can be applied to development of various functional coatings using exfoliated 2D materials with polydispersity.
Abstract Stimuli‐responsive properties of soft materials originate from dynamic structure changes. Layered polydiacetylene (PDA) shows color‐change properties with the application of external stimuli, such as thermal and mechanical stresses. Layered organic materials possessing intercalation capabilities and dynamic properties have potentials for tuning their structures and properties by the intercalated guests. A variety of sensing and imaging devices can be developed by control of the stimuli responsivity. Here, the key structures, processes, and mechanisms for tuning the stimuli‐responsive color‐change properties of layered PDA are studied by in situ analyses with heating and cooling. The in situ analyses indicate that heating initiates thermal motion of the alkyl side chains of the PDA main chain in the host layers around 60 °C, regardless of the type of intercalated guests. Further heating induces torsion of the PDA main chain leading to color changes at different temperatures, depending on the types of the intercalated guest. Then, the layered structure is irreversibly deformed with lowering the crystallinity. The results indicate that the stimuli‐responsive color‐change properties are controlled by the rigidity of the layered structures consisting of the host layers and guests. The control strategy based on rigidity tuning can be applied to a variety of soft materials with stimuli responsivity.
Departmental variations of the hierarchical lamellar structures of whorls, a siphonal canal, and spines of shells of a gastropod Murex pecten (Venus comb) were characterized with comparison of their mechanical properties, such as bending strength and hardness.
Micrometre-thick calcareous shells consisting ofc-axis-oriented calcite nanorods are produced on an organic sheet as mimetics of foraminiferal tests and isopod cornea cuticles.
