Superhydrophobic Polypropylene Surface via Migration of SiO ₂ Nanoparticles with Low Surface Energy

The modification of polypropylene (PP) to achieve increased hydrophobicity while maintaining structural integrity is an important yet challenging task. In this work, by introducing a hydrophobically modified inorganic filler (silica (SiO₂) modified with perfluorooctyltriethoxysilane (FOTS)), m-SiO₂/PP composites are produced via melt blending, then pressing of composites into sheets with different substrates. Measurement of the contact angle gives that when pressed with polytetrafluoroethylene (PTFE) film substrate, the water contact angle of the composite with 20 wt.% m-SiO₂ can reach 140°, which is 44% higher than that of pure PP (97°).By scanning electron microscopy and micro-infrared analysis, when the composites are pressed into sheets with PTFE substrates, m-SiO₂ migrates to its pressed side. This is due to in PTFE, hydrogen atoms in the polyethylene structure are replaced by fluorine atoms, thereby forming a "fluorine generation" protective layer over the carbon-carbon skeleton. Hence, the fact that in PP composites with PTFE platens, fluorosilane chain-encapsulated PTFE sheets and m-SiO₂ are attracted to each other due to the presence of very stable C─F bonds, which have a very low surface energy. This material has self-cleaning properties and is expected to be widely used for protection against dust and oil.