Effect of heterogeneity on hydro/ice-phobic properties of alkylsilane/fluoro-alkylsilane-based coatings on Al substrates

In this work, hydrophobic and anti-ice performances of heterogeneous coatings (HCs) were studied. Multilayer thin films of homogeneous and heterogeneous chemically different alkylsilane compounds, i.e., octadecyltrichlorosilane (OD) and 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PF) were fabricated by alkylsilane/fluoro-alkylsilane deposition on a flat aluminum alloy (AA6061) substrate. The contact angle (CA) values for the homogeneous coatings of OD–OD and PF–PF after a 12-h immersion time (IT) were ~140° and ~120°, respectively. However, significant improvements in CA values were observed for the HCs, PF–OD and OD–PF, with CA values of ~154° and ~160°, respectively, for a 12-h IT. Moreover, very small contact angle hysteresis (CAH) values of ~6°–7° were obtained for PF–OD and OD–PF, whereas large CAH values of ~40°–65° were obtained for the homogeneous coatings. Scanning electron microscopy of the coated surfaces showed a rough structure at the micro-/nano-meter scale and X-ray photoelectron spectroscopy analysis indicated the presence of alkylsilane and/or fluoro-alkylsilane molecules on polished aluminum surfaces. The ice adhesion reduction factor (ARF) of OD–OD and PF–PF homogeneous coatings shows that ice adhesion strength is about 1.5 and 1.7 times lower, respectively, than that obtained on a polished bare Al sample. However, the ARF of PF–OD and OD–PF HCs shows that ice adhesion strength is about 2.7 and 3.5 times, respectively, lower than that obtained on a polished bare Al sample.