Solvent-free synthesis of self-regenerative superhydrophobic film from silicone waste with drag-reduction and selective oil absorption behaviour

Abstract

In the present work, we devised an ecological solution for recycling silicone waste into functionalized films possessing superhydrophobicity with low drag and oil adsorption characteristics. We used two ecological approaches to transform silicone waste into nanoparticles with inherently distinct surface characteristics. These spheroidal silica nanoparticles, with an average size of 150 nm, showed hydrophilic and hydrophobic characteristics. The detailed characterization confirmed hydrophobic silica being grafted with –CH3 oligomers compared to hydrophilic counterparts. These silica nanoparticles were used to fabricate flexible superhydrophobic films through a solvent-free approach. Films synthesized using hydrophilic particles showed better de-wetting characteristics with advancing angle > 150°, low hysteresis (<5°) and sliding angle (<5°) at an optimum volumetric concentration. High de-wetting stability and low adhesion of ∼ 20 μN with water droplet were noticed for these films due to homogenous particle distribution, leading to significant protrusions and favourable line tension. High van der Waals interaction energy aided better mixing of hydrophilic particles in the matrix than the hydrophobic counterpart. This also resulted in high mechanical strength ∼ 7 MPa (matrix strength ∼ 3 MPa) and better robustness under different harsh conditions, sustaining more than ten months of weathering and one month of immersion. Films showed real-time self-regeneration capability, retaining high de-wetting due to surface chemistry and morphology rejuvenation. The film also displayed extremely low drag, promoting water droplet mobility at ∼ 0.5 m/s wind velocity and oil–water separation capability. The fluorine-free flexible superhydrophobic films synthesized using silicone waste exhibited multi-dimensional characteristics for wide-range applications.