Molecular dimensions and surface diffusion assisted mechanically robust slippery perfluoropolyether impregnated mesoporous alumina interfaces

Abstract

Accomplishing mechanically robust omniphobic surfaces is a long-existing challenge, and can potentially find applications in bioengineering, tribology and paint industries. Slippery liquid impregnated mesoporous α-Al2O3 interfaces are achieved with water, alkanes, water based and oil based high viscosity acrylic paints. Incredibly high abrasion-resistance (wear coefficients ≤10−8 mm3 N−1 m−1) and ultra-low friction coefficients (≥0.025) are attained, attributing to the hard alumina matrix and continuous replenishment of perfluoropolyether aided by capillarity and surface diffusion processes. A variety of impregnating liquids employed suggest that large molecules, faster surface diffusion and lowest evaporation rate generate the rare combination of high wear-resistance and omniphobicity. It is noteworthy that these novel liquid impregnated Al2O3 composites exhibit outstanding load bearing capacity up to 350 MPa; three orders of magnitude higher than achievable by the state of the art omniphobic surfaces. Further, our developed thermodynamic calculations suggest that the relative thermodynamic stability of liquid impregnated composites is linearly proportional to the spreading coefficient (S) of the impregnating liquid with the matrix material and is an important tool for the selection of an appropriate matrix material for a given liquid.

Perfluoropolyether-Impregnated Mesoporous Alumina Composites Overcome the Dewetting–Tribological Properties Trade-Off

“…In our previous study 23 These Fomblin ® oil impregnated MPA composites outperforms the traditionally available omniphobic surfaces 12,17,19,36,37 that are approached by Hexadecane molecules. Also, the newly formed surfaces of wear% debris may be devoid of Fomblin ® oil as schematically shown in Figure 1d.…”

“…In the very recent times, Nepenthes Pitcher plant inspired slippery liquid infused porous surfaces (SLIPS) have shown excellent anti%sticking properties 22 , high load bearing capacity 23 , anti%fouling properties 24 , anti%frosting 25 , and anti%icing 26 properties. We exploited this design principle to an anomalous material system which is perfluoropolyether impregnated polar mesoporous α─Al 2 O 3 (MPA) whose surfaces are devoid of protruding micro or nano features or apolar rendering functionalization treatments.…”

“…Sample Preparation and Microstructural Chracterizations: Mesoporous α─Al 2 O 3 green compacts were synthesized by employing slip casting process 23,27,28 . Both cuboidal and cylindrical shaped green compacts were manufactured to utilize them as a tribo pair.…”

“…The microstructural investigations of more than ten sintered and polished samples, and all the abraded samples were performed with Hitachi S4800 high resolution scanning electron microscope (HRSEM) in secondary electron (SE) mode at 1.5 keV acceleration voltage and 10 KA beam current. The sample preparation and the resulting microstructures of unworn samples are highly reproducible as discussed elsewhere 23,27 . Post abrasion, the impregnated…”

“…We utilized commercially available Fomblin ® Y LVAC 25/6 perfluoropolyether for generating both flooding and unflooding configurations (refer to experimental section for preparation) atop impregnated 70%90 % dense MPA sampes as depicted in Figure 1 Hexadecane, Dodecane, Fomblin ® oil wet the alumina surfaces. 23,27 Static contact angles of Hexadecane, Dodecane, water with flat α−Al 2 O 3 are 0° and that of Fomblin ® oil is 18°. 23 .…”