Hirofumi Daiguji

In this tutorial review, recent developments in modeling and experimental studies on nanofludics were reported. Nanofluidic studies were categorized into two groups depending on the characteristic length scale. When the size of the nanochannels and pores is 5-100 nm, electrostatic interactions are dominant, and ion and fluid flow can be analyzed by continuum dynamics. Various nanofluidic devices were proposed to manipulate aqueous solutions and biomolecules at the nanoscale. The successful devel

Theoretical modeling of ionic distribution and transport in silica nanotubes, 30 nm in diameter and 5 μm long, suggest that when the diameter is smaller than the Debye length, a unipolar solution of counterions is created within the nanotube and the coions are electrostatically repelled. By locally modifying the surface charge density through a gate electrode, the ion concentration can be depleted under the gate and the ionic current can be significantly suppressed. It is proposed that this coul

Theoretical modeling of ionic distribution and transport in a nanochannel containing a surface charge on its wall, 30 nm high and 5 microm long, suggests that ionic current can be controlled by locally modifying the surface charge density through a gate electrode, even if the electrical double layers are not overlapped. When the surface charge densities at the right and left halves of a channel are the same absolute value but of different signs, this could form the basis of a nanofluidic diode.

When the Debye length is on the order of or larger than the height of a nanofluidic channel containing surface charge, a unipolar solution of counterions is generated to maintain electrical neutrality. A pressure-gradient-driven flow under such conditions can be used for ion separation, which forms the basis for electrochemomechanical energy conversion. The current−potential (I−φ) characteristics of such a battery were calculated using continuum dynamics. When the bulk concentration is large and

Electroosmotic flow (EOF), a consequence of an imposed electric field onto an electrolyte solution in the tangential direction of a charged surface, has emerged as an important phenomenon in electrokinetic transport at the micro/nanoscale. Because of their ability to efficiently pump liquids in miniaturized systems without incorporating any mechanical parts, electroosmotic methods for fluid pumping have been adopted in versatile applications-from biotechnology to environmental science. To unders

The adsorption–desorption isotherms and relaxation curves of water in chromium terephthalate metal–organic frameworks (MOFs), MIL-101, were measured by the gravimetric method at 298 K and 1 atm. The obtained isotherms were compared to those obtained by the volumetric method, which showed good agreement. The measured isotherms exhibited three-step and two-step curves during adsorption and desorption, respectively. The hysteresis between adsorption and desorption isotherms was not pronounced, and

Water adsorption in MIL-101(Cr) (MIL = Materials Institute Lavoisier) was investigated by molecular simulations. Grand canonical Monte Carlo simulations were performed to understand the pore-filling processes of water in the large, medium, and small cavities of MIL-101(Cr) at different pressures. With increasing pressure, the water molecules first adsorb around unsaturated Cr atoms, forming multimolecular chains and clusters. The simulations show that capillary condensation in the medium and lar

A fabrication method for hollow melamine-formaldehyde microcapsules from microbubble templates is presented. This method is based on the direct encapsulation of microbubbles, and thus does not require a liquid- or solid-core decomposition process. This study determined the conditions for controlling the surface morphology, shell thickness, and diameter distribution of hollow microcapsules. Results showed that the surface morphology of these hollow microcapsules depended on the reaction time, gly

Owing to its high mobility and low sintering temperature, ZnO is a promising electron-transporting layer for flexible and tandem applications of perovskite solar cells. However, ZnO inevitably triggers the degradation of perovskite materials. Such degradation can be inhibited when ZnO films with improved stoichiometry and minimized defects are used. In this work, a high efficiency with substantial stability of ZnO-based perovskite solar cells is achieved using a high-working-pressure sputtering