Gradient Porous Structure Templated by Breath Figure Method.

Surfaces with gradient topography are important in various fields but are difficult to fabricate. Herein, we report a facile and robust way to fabricate a surface with gradient topography of porous structure, in one direction, based on the breath figure (BF) method for the first time. The influencing factors including relative humidity (RH), sample immersion time, and solvent composition, affecting the speed, time, and model of the droplet growth, respectively, were investigated to control gradient BF pores with different ranges of pore sizes. Applying appropriate parameters, gradient BF pores with a diameter difference over 400% were prepared on one sample. The mechanism of gradient duration of solvent evaporation at different regions of a sample for fabricating gradient pores was proposed and experimentally verified with recording optical and thermographic changes of the sample in the BF procedure. This new method provides a novel site for gradient topography fabrication.