Liquid droplet evaporation from buckypaper: On the fundamental properties of the evaporation profile

Abstract

Buckypaper is a mesoporous, self-supporting, electrically conducting mat of multiwall carbon nanotubes prepared by filtering a nanotube suspension through a submicron pore diameter membrane and drying the filter cake. Multiple phenomena take place simultaneously when a liquid droplet contacts the buckypaper surface: wetting, spreading, adsorption, capillary filling, evaporation from the surface, evaporation from the pores, infiltration of nanotube–nanotube junctions, gravity induced convective flow, etc. The electrical resistance of the buckypaper as a function of time exhibits a maximum curve during these processes. The fine details of the shape of this curve are slightly different for every solvent. We refer to this characteristic function as the evaporation profile of the studied liquid. In this paper we combine simultaneous electrical resistivity measurement, weight measurement and visible image processing methods to reveal the basic properties of the evaporation profile. A good correlation between the changes in buckypaper mass and electrical resistance was found and the distribution of the liquid penetrating the buckypaper matrix followed specific patterns and was correlated with the shape of the measured evaporation profile. Results are compared with fluid dynamic simulations. The evaporation profile emerges as a reproducible and inexpensive qualitative analytical tool for liquid identification. Alternatively, recording the evaporation profile of a chosen test liquid could become a feasible characterization method for mesoporous materials.