The wetting and pagoda instability (PI) on soluble fibers.

We discover a new kind of instability when inserting a soluble fiber into liquid. Because the dissolved fiber looks like a Chinese pagoda, we designate this instability as pagoda instability (PI). During the process of PI, coupling of dissolution and wetting leads to special phenomena, i.e. periodic instability, dissolving-induced jet flow, etc., and optimizes the fiber shape, which can be used to screen the capillary force. In this paper, we study PI of moving contact line on the surface of soluble fibers, obtain a phase diagram of the different shapes of the dissolved fibers, reveal evolution dynamics and mechanisms of the interface and the energy influenced by the competition between interface energy and chemical potential, and propose a criterion of PI to predict the occurrence of PI and shape of the dissolved fibers. At the end of this paper, to show the important application of PI, we design and prepare a new AFM tip, which can shield the precision of AFM measurement from the capillary effect caused by ambient humidity, liquid film, etc.