posted on 2016-02-18, 17:26authored byChihiro Urata, Benjamin Masheder, Dalton
F. Cheng, Atsushi Hozumi
From a viewpoint of reducing the
burden on the environment and
human health, an alternative method for preparing liquid-repellent
surfaces without relying on the long perfluorocarbons (C((X–1)/2)FX, X ≥ 17) has been strongly demanded lately. In this
study, we have successfully demonstrated that dynamic dewettability
toward various probe liquids (polar and nonpolar liquids with high
or low surface tension) can be tuned by not only controlling surface
chemistries (surface energies) but also the physical (solid-like or
liquid-like) nature of the surface. We prepared smooth and transparent
organic–inorganic hybrid films exhibiting unusual dynamic dewetting
behavior toward various probe liquids using a simple sol–gel
reaction based on the co-hydrolysis and co-condensation of a mixture
including a range of perfluoroalkylsilanes (FASX,
C((X–1)/2)FXCH2CH2Si(OR)3, where X = 3, 9, 13, and 17) and tetramethoxysilane (Si(OCH3)4, TMOS). Dynamic contact angle (CA) and substrate
tilt angle (TA) measurements confirmed that our FASX-hybrid films exhibited excellent dynamic dewetting properties and
were mostly independent of the length of perfluoroalkyl (Rf) groups. For example, 10 μL droplets of ultralow surface tension
liquids (e.g., diethyl ether (γ = 16.26 dyn/cm) and n-pentane (γ = 15.51 dyn/cm)) could move easily on
our FAS9-, FAS13-, and FAS17-hybrid film surfaces at low substrate
TAs (<4°) without pinning. This is comparable or superior
to the best perfluorinated textured and flat surfaces reported so
far. This exceptional dynamic dewetting behavior appeared only when
TMOS molecules were added to the precursor solutions; we assume this
is due to co-condensed TMOS-derived silica species working as spacers
between the neighboring Rf chains, enabling them to rotate
freely and in doing so provide a surface with liquid-like properties.
This led to the distinguished dynamic dewettability of our hybrid
films, regardless of the small static CAs. Our FASX-hybrid films also displayed excellent chemical and physical durability
against thermal stress (∼250 °C), high-temperature (150
°C) oil vapor, and various other media (perfluoro liquid, boiling
water, and weak acid) without degrading their dynamic dewettability.
Such exceptional durability has been rarely seen on conventional perfluorinated
surfaces reported so far.