In Situ Identification of Dewetting-Induced Large-Scale Deformation of Vertically Aligned Single-Walled Carbon Nanotubes*

We investigated dynamical processes of capillary-mediated deformation of vertically aligned single-walled carbon nanotubes (VA-SWCNTs) via {\it in situ} observation of their wetting and dewetting behaviors using an environmental scanning electron microscope. Three types of wetting behaviors on a VA-SWCNT sample were observed, namely conical shaped water aggregates, spherical droplets on tips of conical shaped water aggregates, and extensively distributed water layers. The former two types both resulted in dimples on the VA-SWCNT surface, failing to induce large-scale deformation of VA-SWCNTs. In contrast, the latter caused the formation of wall-like structures and crack propagation in the VA-SWCNT film during the dewetting process due to directional retraction of vapor-liquid interfaces. Compared to the previous studies based on {\it ex situ} observations of dried samples, our {\it in situ} observation successfully captured temporal evolution of the dewetting-induced deformation, which represents initial stages of capillary processes that lead to the self-organization of VA-SWCNTs reported in recent literatures.