Cationic “hard–soft” Janus particles for hydrophobic modification of cellulose paper

Paper is an abundant, biodegradable, inexpensive, renewable, and versatile material in our daily life. However, paper is vulnerable to water and thus loses its mechanical properties and durability. Hydrophobic modification of paper surface is often a prerequisite to expand utilizations of paper. Herein, we synthesized cationic “hard–soft” Janus particles via seeded emulsion polymerization for hydrophobic modification of cellulose paper. The cationic “hard–soft” Janus particles consisted of two hemispheres that possess distinct glass transition temperatures ( T g). In the sizing and drying process, the soft hemispheres with low T g deformed and formed films to enhance the adhesion between the hard hemispheres and fiber surface. The hard hemispheres with high T g remained intact and formed nanoscale hierarchical roughness on cellulose surface to enhance the hydrophobicity of sized paper. The positive charges of cationic "hard–soft" Janus particles promoted their adsorption on cellulose fibers. The mechanical properties and water resistance of sized paper were significantly improved by cationic “hard–soft” Janus particles. The abrasion test demonstrated the cationic “hard–soft” Janus particles can protect the paper from external damages to a certain extent. This facile method shows that Janus particles have the potential to combine different materials to provide tailor-made properties on a diverse range of substrates.