Development of superhydrophobicity in fluorosilane-treated diatomaceous earth polymer coatings

[Display omitted] •Inexpensive superhydrophobic coatings can be made using fluorosilane treated diatomaceous earth (DE) in simple polymer-particle systems.•A minimum amount (1.2%) of fluorinated silane coupling agents was required to make diatomaceous earth particles superhydrophobic.•A minimum of 40% treated (DE) with high molecular mass polymer binders was required to make superhydrophobic coatings.•Untreated and treated diatomaceous earth behave differently in polymer coatings.•After achieving superhydrophobicity, the water contact angles became independent of the polymeric binder used. Superhydrophobic coatings were prepared using 3-(heptafluoroisopropoxy)- propyltrimethoxysilane (HFIP-TMS) treated diatomaceous earth (DE) particles with high molecular mass polystyrene or poly(vinyl acetate) as polymer binders. DE is a highly hydrophilic material and treatment of the DE with HFIP-TMS turned it into superhydrophobic diatomaceous earth (HFIP-DE). Thermogravimetric analysis (TGA) was used to determine the amount of grafted fluorosilane on the surface of the DE particles. The results showed that approximately 1.8% of HFIP-TMS grafted onto the surface of DE particles resulted in superhydrophobicity with contact angles as high as 164° for the particles themselves and also in coatings. Fourier transformed infrared spectroscopy (FTIR) was used to confirm the presence of HFIP-TMS on the surface of DE particles. The development of the hydrophobicity in the coatings with either polystyrene (PS) or poly(vinyl acetate) (PVAc) as binders was followed as a function of the particle loading using contact angle measurements and scanning electron microscopy. It was found that for these model DE-binder systems, the contact angles of the coatings were independent of the polymers used as long as the particle loading was greater than a minimum amount (∼40% treated DE particles). It was also found that more treated DE particles moved to the air interface as the particle loadings in the coatings increased and then levelled off.