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Nanobubbles exist at solid–liquidinterfaces between purewater and hydrophobic surfaces with very high stability, lasting incertain cases up to several days. Not only semispherical but alsoother shapes, such as micropancakes, are known to exist at such interfaces.However, doubt has been raised as to whether or not the nanobubblesare gas-phase entities. In this study, surface nanobubbles at a purewater–highly ordered pyrolytic graphite (HOPG) interface wereinvestigated by peak force quantitative nanomechanics (PF-QNM). Multipleisolated nanobubbles generated by the solvent-exchange method werepresent on the terraced areas, avoiding the steps of the HOPG surface.Adjacent nanobubbles coalesced and formed metastable nanobubbles.Coalescence was enhanced by the PF-QNM measurement. We determinedthat nanobubbles can exist for a long time because of nanoscale contactangle hysteresis at the water–HOPG interface. Moreover, thehydrophilic steps of HOPG were avoided during coalescence, providingevidence that the nanobubbles are truly gas phase. [ABSTRACT FROM AUTHOR]

We studied the dependence on tacticity of the dynamic phase separation behavior of thermoresponsive poly( N, N-diethylacrylamide) (PDEA) in an aqueous solution. Using a laser temperature-jump technique combined with transient photometry, we determined the time constants of the phase separation and found that both atactic and isotactic-rich PDEAs had fast and slow phase separation processes (τ fast and τ slow ). The fast process (τ fast ) was independent of the tacticity, irrespective of the concentration. On the other hand, the slow process had a strong dependence on the tacticity. We found the slow phase separation process got considerably faster with increasing isotacticity in dilute solutions. This effect due to the tacticity of the PDEA is totally different from that of poly( N-isopropylacrylamide) and can be explained on the basis of the difference between the hydrophobicity of atactic PDEA and that of isotactic-rich PDEA.

Water condensation on a hybrid hydrophilic-hydrophobic surface was investigated to reveal nucleation mechanisms at the microscale. Focused ion beam (FIB) irradiation was used to change the wettability of the hydrophobic surface with 10 nm order spatial resolution. Condensation experiments were conducted using environmental scanning electron microscopy; droplets, with a minimum diameter of 800 nm, lined up on the FIB-irradiated hydrophilic lines. The heterogeneous nucleation theory was extended to consider the water molecules attracted to the hydrophilic area, thereby enabling explanation of the nucleation mechanism under unsaturated conditions. Our results showed that the effective surface coverage of the water molecules on the hydrophilic region was 0.1-1.1 at 0.0 °C and 560 Pa and was dependent on the width of the FIB-irradiated hydrophilic lines and hydrophobic area. The droplet nucleation mechanism unveiled in this work would enable the design of new surfaces with enhanced dropwise condensation heat transfer.