Capillary-Induced Wrinkle-to-Fold Transitions Under Biaxial Compression.

Wrinkles in bilayer systems comprising a thin stiff film attached to a soft substrate can globally transition into folds under sufficiently large compression. This phenomenon has been extensively studied primarily using uniaxially compressed systems. However, inducing the wrinkle-to-fold transition at designated locations on a wrinkled surface under small biaxial compression remains a challenge. In this study, we describe a method for causing randomly oriented wrinkles to locally evolve into folds using water droplets. When a droplet comes into contact with the random wrinkles that have spontaneously formed upon film deposition owing to residual biaxial compressive strains, radially extended folds instantaneously emerge at the droplet boundary. Upon water evaporation, the wrinkles beneath the droplet also undergo a transition, leaving a fold network. By contrast, the surface regions distant from where the droplet was placed retain the wrinkle morphology. The folded areas can be controlled by adjusting the volume and number of droplets. These transitions are enabled by the capillary forces of water that help to increase the local compressive strains. This capillary-induced wrinkle-to-fold transition provides a simple mechanism to develop folds in selected locations on wrinkled surfaces of film-substrate systems subject to small biaxial compression, which is unachievable with conventional approaches.

Manganese-mediated C3-selective direct alkylation and arylation of 2-pyridones with diethyl malonates and arylboronic acids.

A manganese-mediated dehydrogenative direct alkylation of 2-pyridones with diethyl malonates has been developed. A similar reaction system is applicable to the direct arylation with arylboronic acids. These manganese-based reactions occur regioselectively at the C3 position of the 2-pyridones. The observed high C3 regioselectivity can complement precedented C-H functionalization protocols of the 2-pyridones in view of the site selectivity.

Nickel-catalyzed direct alkylation of heterocycles with α-bromo carbonyl compounds: C3-selective functionalization of 2-pyridones.

Nickel HAS it: A Ni(cod)2/dppp catalyst system promotes the direct alkylation of electron-rich heterocycles with α-bromo carbonyl compounds and involves an alkyl radical intermediate (see scheme; cod = 1,5-cyclooctadiene, dppp = 1,3-bis(diphenylphosphino)propane). This homolytic radical aromatic substitution (HAS)-type reaction enables the C3-selective direct functionalization of 2-pyridones.

Modulational instability of zone boundary mode and band edge modes in nonlinear diatomic lattices.

We analyze the modulational instability of the zone boundary mode (ZBM) and the band edge modes (BEMs) in a one-dimensional nonlinear diatomic lattice and obtain rigorous results. Some numerical calculations of modulational instability in these modes are presented. These results indicate that the modulational instability of the BEMs leads to excitation of the discrete breathers (DBs) in the band gap, while that of the ZBM leads to excitation of the DBs above the phonon band.

Unlocalized crack initiation and propagation in staggered biomaterials.

Many types of tissues in living organisms exhibit a combination of different properties to fulfil their mechanical functions in complex environments. Nacre with more than 90% brittle and hard phase and a little protein matrix, exhibits high strength and toughness, which is difficult to achieve in artificial materials. Researchers have shown that the toughness of nacre is related to the cracking process. Most of them, however, assume an obvious pre-existing crack on the model and the initiation of the microscopical pre-existing crack is not considered yet. Based on fracture mechanics with the cohesive zone model, we reveal the mechanism of the crack initiation and propagation pattern in staggered biomaterials without any pre-existing crack. The simulation result shows that there are two crack propagation modes: localized mode and unlocalized mode. A crack initiates and propagates in a small area in the localized mode, while cracks initiate at different points and propagate in various paths in the unlocalized mode. The crack initiation mechanism from the intrinsic properties of the material is clarified using energy based stability analysis. The result shows that the shear interfacial mechanism significantly delays the crack initiation.

A concise access to (polyfluoroaryl)allenes by Cu-catalyzed direct coupling with propargyl phosphates.

A copper-based catalyst system for the direct coupling of polyfluoroarenes with propargyl phosphates has been developed. The catalysis can provide a rapid and concise access to (polyfluoroaryl)allenes, which can be important building blocks for the synthesis of fluorinated functional materials.

Refolding of fully reduced bovine pancreatic trypsin.

Refolding of bovine pancreatic trypsin was carried out. When starting with denatured S-S intact trypsin, the recovered activity attained was 95-100%. In contrast, the recovered activity after refolding denatured S-S reduced trypsin was considerably low compared with other proteases that have been worked with previously. Such low recovered activity was attributed to the small amount of fully reduced trypsin used as starting material for complete refolding. Taking this into account, a recovered activity of 86% could be achieved when using inhibitor-immobilized gels.

Hydrogen bond dynamics and microscopic structure of confined water inside carbon nanotubes.

We have investigated the density and temperature dependences of microscopic structure and hydrogen bond dynamics of water inside carbon nanotubes (CNTs) using molecular dynamics simulation. The CNTs are treated as rigid, and smoothly truncated extended simple point charge water model is adopted. The results show that as the overall density increases, the atomic density profiles of water inside CNTs become sharper, the peaks shift closer to the wall, and a new peak of hydrogen atomic density appears between the first (outermost) and second layer. The intermittent hydrogen bond correlation function C(HB)(t) of water inside CNTs decays slower than that of bulk water, and the rate of decay decreases as the tube diameter decreases. C(HB)(t) clearly decays more slowly for the first layer of water than for other regions inside CNTs. The C(HB)(t) of the interlayer hydrogen bonds decays faster than those of the other regions and even faster than that of the bulk water. On the other hand, the hydrogen bond lifetimes of the first layer are shorter than those of the inner layer(s). Interlayer hydrogen bond lifetimes are clearly shorter than those of the constituent layers. As a whole, the hydrogen bond lifetimes of water inside CNTs are shorter than those of bulk water, while the relaxation of C(HB)(t) is slower for the confined water than for bulk water. In other words, hydrogen bonds of water inside CNTs break more easily than those of bulk water, but the water molecules remain in each other's vicinity and can easily reform the bonds.

Flow structure of water in carbon nanotubes: poiseuille type or plug-like?

We have conducted molecular dynamics simulations of water flow in carbon nanotubes (CNTs) for (6,6) to (20,20) CNTs at a streaming velocity of 100 ms. The fluidized piston model (FPM) and the ice piston model (IPM) are employed to drive flow through the CNTs. The results show that the single-file water flow inside (6,6) CNT has a convex upward streaming velocity profile, whereas the velocity profiles in (10,10) to (20,20) CNTs are flat except near the tube wall. The flow structure of cylindrical water in the (8,8) CNT is intermediate between that for the (6,6) CNT and the larger CNTs. The flow parameters are found not to exhibit any dependence on streaming velocity at up to 300 ms in the (12,12) CNT. The hydrogen bond lifetimes of water flowing in CNTs tend to be longer than for the corresponding equilibrium states, and nonzero flow does not reduce the microscopic structure or structural robustness (hydrogen bond lifetime). Although the atomic density profile varies with tube diameter, reflecting the change in static microscopic structure of flow from single file to cylindrical, tube diameter does not induce a clear transition in streaming velocity, temperature, or hydrogen bond lifetime over this diameter range. The results suggest that water flow in CNTs of this size is more pluglike than Poiseuille type, although the flow structure does not strictly accord with either definition.