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Background: There are many patents on design of a material surface with special wetting property, however, theoretical methods are lacked. The wetting property of a nanofiber member has attracted much attention. A material with different sizes or with different structures possesses different wetting properties. No theory can explain the phenomenon. Methods: The contact angle, fiber fineness, pore size and layer of the nanofiber membrane were tested. The contact angles were measured for membranes with different thicknesses. The geometrical potential is used to explain the experimental phenomenon. Results: The wetting property of a nanofiber membrane mainly depends on fiber diameter and thickness. Conclusion: Wetting property of a PVA nanofiber membrane depends upon not only the hydrophilic groups, but also the geometrical structure of its surface, the latter prevails when the porous size of the membrane tends to a nanoscale, and the wetting property can be inverted from hydrophilicity to hydrophobicity.

PACS 45.50.Tn -Dynamics and kinematics of a particle and a system of particles: Collisions PACS 45.70.Vn -Granular models of complex systems; traffic flow PACS 05.65.+b -Self-organized systems Abstract -An experimental study of the behavior of hollow balls filled with some granules (mung beans or millets) bouncing repeatedly off a static flat horizontal surface is presented. We observed that the bounce number of the ball is limited and decreases regularly with an increasing number of granules. Moreover, for two balls containing a different kind of granules, their bounce numbers are basically equal when the two balls have the same mass of granules. While there is no clear relationship between the first rebound height of one ball and the number of granules, there appears an exponential decay of the second rebound height with an increase of the granule number. Furthermore, a two-dimensional numerical model has been created to find out the law of the ball's rebound height and the dissipation law of the granule nested system. A generalized prediction equation to reasonably explain the law of the bounce number has also been proposed.