Cobalt (II) chloride promoted formation of honeycomb patterned cellulose acetate films

► Honeycomb patterned films were prepared from cellulose acetate (CA)/CoCl2 solutions. ► Water droplets condensed on the (CA)/CoCl2 solution surface act as a template. ► Size and pore regularity in films depends on the CA/CoCl2 molar ratio and humidity. ► Pore formation is caused by hygroscopicity of CoCl2 and its low interaction with CA.