In-situ design of hierarchical durable silica-based coatings on polypropylene films with superhydrophilic, superhydrophobic and self-cleaning properties

Superhydrophobic surfaces are receiving increasing attention due to their real-world applications. However, these surfaces suffer from a lack of durability and complicated synthetic processes. This research uses a combination of a simple in-situ coating process between oxygen-activated polypropylene films and unreacted silane monomers. The in-situ process uses a modified Stöber method with the addition of the surfactant cetyltrimethylammonium bromide (CTAB) which aggregates silica (SiO ₂) particles in a basic aqueous solution. This resulted in a layer of covalently bonded hierarchical coating of individual and aggregated SiO ₂ “flakes” and particles. These coatings were found to have at least double the surface roughness than samples prepared without CTAB with superhydrophilic properties due to their high surface roughness and hydrophilic surface chemical groups. A second layer of fluorocarbon silane monomers was reacted with the hydroxyl groups on the hierarchical SiO ₂ coating resulting in films with excellent superhydrophobic and self-cleaning properties. The sample containing aggregated SiO ₂ particle structures exhibited higher chemical and physical durability against external irritations including adhesion, different pH levels, detergent, abrasion and UV radiation by retaining high contact angles and low rolling angles. Samples coated with flake structures were negatively affected by mechanical irritations. This simple in-situ SiO ₂ coating process in combination with different concentrations of CTAB has not been investigated and has promising potential for many practical applications such as superhydrophilic, superhydrophobic and self-cleaning surfaces.