PDMS/camphor soot composite coating: towards a self-healing and a self-cleaning superhydrophobic surface

A novel self-cleaning polymer composite with self-healing ability to self-repair after chemical and mechanical damage using readily available materials like polydimethylsiloxane (PDMS) and camphor soot particles is developed. With the optimal loading of the camphor soot particles, the composite coating on glass and stainless steel surfaces reveals self-cleaning properties with a water contact angle of 171 degrees. We also demonstrate that any degradation of its surface energy under oxygen plasma etching can be recuperated, demonstrating the self-healing ability of the superhydrophobic surface. The fabricated PDMS/camphor soot hybrid coating exhibited excellent retention of superhydrophobicity against the impact of sand particles from a height of 10-70 cm. In addition, after being damaged chemically by strong acid treatment (1 M HNO3 solution), the coating can also restore its properties after a short thermal cycle. The quantitative measurement of mechanical properties of self-healing superhydrophobic surfaces is challenging due to their high surface roughness at the micro/nano-scale with a tolerance of low stress. In this work, we have conducted a detailed investigation of the mechanical responses of the camphor soot particle-incorporated PDMS composites by using atomic force microscopy (AFM). Using an AFM tip with a radius of approximately 10 nm, we have quantified different mechanical properties such as stiffness, the plastic work, and the effective adhesive work. Such versatile superhydrophobic surfaces can have wide applications ranging from underwater marine vessels to coating surfaces to protect them from moisture and unwanted penetration of water. These composite coatings are environmentally benign and can be readily coated on various substrates by simple spraying.