Formation mechanism of ordered porous nitrocellulose membranes by breath figure templating

Nitrocellulose (NC) membrane is a widely utilized component in biosensors due to its tunable porous structure and the ability to immobilize protein. The commercial NC membrane is produced via evaporation induced phase separation technique, in which the condensed water could be induced inevitably, leading to the difficulty in precise control of porous structure. To clarify the influence of condensed water on the phase separation behavior of NC membrane separately, the formation mechanism of NC/Methyl acetate (MA) and NC/Acetone solutions is investigated systematically via in-situ optical microscopy observation, infrared thermal imaging and scanning electron microscopy. It is found that the NC/MA system obeys the traditional breath figure (BF) mechanism due to the high hydrophobicity of MA. When the solution surface temperature drops below the dew point during evaporation, water droplets start to condense and self-assemble on the solution surface to form orderly packed pores. On the other hand, owing to the strong hydrophily of acetone, the pore formation mechanism of NC/ Acetone system is the combination of vapor induced phase separation and immersion precipitation. The solution absorbs water vapor from air spontaneously, meanwhile, condensed water droplets are created during evaporation. BF pattern pores can also be initiated on the surface via precise control of dynamics. In addition, these NC membranes with honeycomb pores are successfully applied for cell culture. This work provides an effective way to design NC membranes with desired porous structure and tunable performances.