Building Dual-Scale Roughness Using Inorganic Pigments for Fabrication of Superhydrophobic Paper

This study reports the fabrication of superhydrophobic paper via a facile two-step dip coating method. Ground calcium carbonate (GCC) and montmorillonite (MTM) were used as inorganic pigment nanoparticles, and cellulose nanofibers were utilized as a binder to study the effect of forming a superhydrophobic surface on filter paper with alkyl ketene dimer (AKD) treatment. The micro GCC-treated paper showed a contact angle of 156.7 ± 2.4° but a relatively large tilt angle (∼15°). Counterintuitively, the nano MTM-treated paper surface was only hydrophobic with large hysteresis even after AKD sizing three times. Although none of the pigments by themselves could form good performance superhydrophobic coating on paper, by combining the two pigments, we built MTM nanostructures on top of the GCC micrometer-structures to form a surface with dual-scale roughness. The contact angle measurements showed that the MTM/GCC treated paper had a contact angle of 162.4 ± 3.3° and a tilt angle of less than 5°.