||Hideaki Teshima, Takashi Nishiyama, Koji Takahashi, Nanoscale pinning effect evaluated from deformed nanobubbles, Journal of Chemical Physics, 10.1063/1.4973385, 146, 1, 2017.01, Classical thermodynamics theory predicts that nanosized bubbles should disappear in a few hundred microseconds. The surprisingly long lifetime and stability of nanobubbles are therefore interesting research subjects. It has been proposed that the stability of nanobubbles arises through pinning of the three-phase contact line, which results from intrinsic nanoscale geometrical and chemical heterogeneities of the substrate. However, a definitive explanation of nanobubble stability is still lacking. In this work, we examined the stability mechanism by introducing a "pinning force." We investigated nanobubbles at a highly ordered pyrolytic graphite/pure water interface by peak force quantitative nano-mechanical mapping and estimated the pinning force and determined its maximum value. We then observed the shape of shrinking nanobubbles. Because the diameter of the shrinking nanobubbles was pinned, the height decreased and the contact angle increased. This phenomenon implies that the stability results from the pinning force, which flattens the bubble through the pinned three-phase contact line and prevents the Laplace pressure from increasing. The pinning force can also explain the metastability of coalesced nanobubbles, which have two semispherical parts that are joined to form a dumbbell-like shape. The pinning force of the semispherical parts was stronger than that of the joint region. This result demonstrates that the contact line of the semispherical parts is pinned strongly to keep the dumbbell-like shape. Furthermore, we proposed a nanobubble generation mechanism for the solvent-exchange method and explained why the pinning force of large nanobubbles was not initially at its maximum value, as it was for small nanobubbles..
||Hideaki Teshima, Koji Takahashi, Yasuyuki Takata, Takashi Nishiyama, Wettability of AFM tip influences the profile of interfacial nanobubbles, Journal of Applied Physics, 10.1063/1.5010131, 123, 5, 2018.02, To accurately characterize the shape of interfacial nanobubbles using atomic force microscopy (AFM), we investigated the effect of wettability of the AFM tip while operating in the peak force tapping (PFT) mode. The AFM tips were made hydrophobic and hydrophilic by Teflon AF coating and oxygen plasma treatment, respectively. It was found that the measured base radius of nanobubbles differed between AFM height images and adhesion images, and that this difference depended on the tip wettability. The force curves obtained during the measurements were also different depending on the wettability, especially in the range of the tip/nanobubble interaction and in the magnitude of the maximum attractive force in the retraction period. The difference suggests that hydrophobic tips penetrate the gas/liquid interface of the nanobubbles, with the three phase contact line being pinned on the tip surface; hydrophilic tips on the other hand do not penetrate the interface. We then quantitatively estimated the pinning position and recalculated the true profiles of the nanobubbles by comparing the height images and adhesion images. As the AFM tip was made more hydrophilic, the penetration depth decreased and eventually approached zero. This result suggests that the PFT measurement using a hydrophilic tip is vital for the acquisition of reliable nanobubble profiles..
||Hideaki Teshima, Yasuyuki Takata, Koji Takahashi, Adsorbed gas layers limit the mobility of micropancakes, Applied Physics Letters, 10.1063/1.5113810, 115, 7, 2019.08, In contrast to surface nanobubbles, the properties of atomically flat gas phases such as micropancakes remain unclear. In this study, we investigated nanoscopic gas phases existing at the interface between highly ordered pyrolytic graphite and air-supersaturated pure water using high-sensitivity frequency-modulation atomic force microscopy (AFM). Micropancakes appeared on a disordered gas layer overlying an ordered gas layer and moved in the direction of AFM scanning. Their movement stopped at the edge of the disordered gas layers, whereas the two gas layers did not move at all. The limited mobility of micropancakes is explained by assuming that the disordered and ordered gas layers, which are composed of strongly adsorbed gas molecules, behave like solid surfaces, and that the surface heterogeneity between them results in a pinning effect..
||Hideaki Teshima, Naoto Nakamura, Qin Yi Li, Yasuyuki Takata, Koji Takahashi, Zigzag gas phases on holey adsorbed layers, RSC Advances, 10.1039/d0ra08861g, 10, 73, 44854-44859, 2020.11, We report for the first time a zigzag-shaped gas phase at a highly-ordered pyrolytic graphite/water interface. The novel shape of the gaseous domain is triggered by the holes of the underlying solid-like layers, which are composed of air molecules. Specifically, many holes were created by heating in the thin solid-like layers, which roughened them. The gas domains that formed on these layers deformed from circular to zigzag-shaped as the contact lines expanded while avoiding the holes of the underlying layers. We explained the formation and growth processes of these gas structures in terms of thin film growth, which varies with the mobility of the constituent molecules. This journal is.
||Hideaki Teshima, Sirshendu Misra, Koji Takahashi, Sushanta K. Mitra, Precursor-Film-Mediated Thermocapillary Motion of Low-Surface-Tension Microdroplets, Langmuir, 10.1021/acs.langmuir.0c00148, 36, 19, 5096-5105, 2020.05, In contrast to microdroplet condensation with high contact angles, the one with low contact angles remains unclear. In this study, we investigated dynamics of microdroplet condensation of low-surface-tension liquids on two flat substrate surfaces by using reflection interference confocal microscopy. Spontaneous migration toward relatively larger droplets was first observed for the microdroplets nucleated on the hydrophilic quartz surface. The moving microdroplets showed a contact angle hysteresis of a0.5°, which is much lower than the values observed on typical flat substrates and is within the range observed on slippery lubricant-infused porous surfaces. Because the microdroplets on the hydrophobic polydimethylsiloxane surface did not move, we concluded that the ultrathin precursor film is formed only on the hydrophilic surface, which reduces a resistive force to migration. Also, reduced size of droplets promotes the thermocapillary motion, which is induced by a gradient in local temperature inside a small microdroplet arising due to the difference in size of adjacent droplets..
||Sota Hirokawa, Hideaki Teshima, Pablo Solís-Fernández, Hiroki Ago, Yoko Tomo, Qin Yi Li, Koji Takahashi, Nanoscale Bubble Dynamics Induced by Damage of Graphene Liquid Cells, ACS Omega, 10.1021/acsomega.0c01207, 5, 19, 11180-11185, 2020.05, Graphene liquid cells provide the highest possible spatial resolution for liquid-phase transmission electron microscopy. Here, in graphene liquid cells (GLCs), we studied the nanoscale dynamics of bubbles induced by controllable damage in graphene. The extent of damage depended on the electron dose rate and the presence of bubbles in the cell. After graphene was damaged, air leaked from the bubbles into the water. We also observed the unexpected directional nucleation of new bubbles, which is beyond the explanation of conventional diffusion theory. We attributed this to the effect of nanoscale confinement. These findings provide new insights into complex fluid phenomena under nanoscale confinement..
||Hideaki Teshima, Qin Yi Li, Yasuyuki Takata, Koji Takahashi, Gas molecules sandwiched in hydration layers at graphite/water interfaces, Physical Chemistry Chemical Physics, 10.1039/d0cp01719a, 22, 24, 13629-13636, 2020.06, Hydration structures are ubiquitous at solid/liquid interfaces and play a key role in various physicochemical and biological phenomena. Recently, it has been reported that dissolved gas molecules attracted to hydrophobic surfaces form adsorbed gas layers. Although a hydration structure and adsorbed gas layers coexist on the surface, the relationships between them remain unknown. In this study, we investigated a highly ordered pyrolytic graphite/pure water interface with and without adsorbed gas layers using frequency-modulation atomic force microscopy. We penetrated the adsorbed gas layers with the strong load force of the AFM tip and thereby obtained the frequency shift curves inside them. By comparing the curves with those measured on a bare HOPG surface, we found that the adsorbed gas layers were located at regions where the molecular density of water was low and were sandwiched between hydration layers with high water density. Moreover, the distance between adjacent hydration layers was larger than that predicted by simulations and was the same with and without the adsorbed gas layers. We propose that gas molecules on the hydrophobic surface interact with the hydration structure before forming the adsorbed gas layers, and extend the distance between hydration layers. This journal is.