Extensive research on the preparation of superhydrophobic surfaces has been reported in the past decade, ranging from basic research to practical applications. Such surfaces usually exhibit water contact angles (CAs) larger than 1508. However, studies on superoleophobic surfaces, on which nonpolar (NP) liquid droplets (in particular, small volumes ca. 3-5 mL) that have appreciably low surface tensions (LSTs) can easily roll across and off, and which have a minimum tilt angle (TA) for droplet motion of less than 108, [1][2][3] are rare, despite of the practical advantages they offer. It is very challenging to fabricate surfaces that strongly promote dewetting of NP liquids, such as n-hexadecane and n-dodecane, because of their LSTs (g lv = 27.5 and 25.4 dyn cm À1 at 20 8C, respectively [4] ). When most superhydrophobic surfaces encounter such NP-LST liquids, they exhibit Wenzel wetting behavior: the liquid droplet sticks to the surface and does not roll off or dewet at any TA (poor dynamic oleophobicity). [5] Although textured surfaces with low surface energy usually maintain high advancing CAs (q A ), when the high-surface-tension (HST) liquid is replaced with a NP-LST one, receding CAs (q R ) are greatly decreased, which results in marked increases in CA hysteresis values (Dq = q A Àq R ). However, a few reports have described the formation of superoleophobic surfaces that are capable of preserving the excellent mobility of NP-LST liquid droplets. [2,3] Tuteja et al. [2] successfully fabricated perfluorinated patterned surfaces with a q A value of more than 1508 and TA = 158 for a 10 mL drop of n-octane (g lv = 21.8 dyn cm À1 at 20 8C [4] ). Zhang and Seeger [3] also prepared a superoleophobic surface consisting of CF 3 -terminated oxidized-silicone nanofilaments with topographical features similar to the "perfectly hydrophobic surface" reported by Gao and McCarthy. [6a] In that case, the minimum TAs needed for movement of 5 mL droplets of NP-LST liquids, such as n-decane (g lv = 23.8 dyn cm À1 at 20 8C [4] ) and nhexadecane, was only approximately 2-58. [3] For the prepara-tion of surfaces with such excellent dynamic oleophobicity, Zhang and Seeger [3] emphasized the necessity of producing weak interactions between the NP-LST droplets and the substrate surfaces.In contrast to such topographically modified surfaces, there have only been a few reports of flat or smooth surfaces with a low CA hysteresis value for both HST and NP-LST liquids. Proper control of both the molecular architecture (branched or ring-shaped molecules) and the physical nature of the modified surface (liquid-like surface that results from high mobility of functional groups in the surface-tethered molecules) are required to realize excellent dynamic dewetting behavior and to allow HST/NP-LST liquid droplets to easily dewet from the surface at low TAs, independent of the magnitude of the CA (this is a practical definition of "ultralyophobic"). [6b] Fadeev and McCarthy [7] and several other groups [8] have previously reported ultralyophobic ...

Seamless control of resistance to liquid drop movement for polar (water) and nonpolar alkane (n-hexadecane, n-dodecane, and n-decane) probe liquids on substrate surfaces was successfully demonstrated using molten linear poly(dimethylsiloxane) (PDMS) brush films with a range of different molecular weights (MWs). The ease of movement of liquid drops critically depended on polymer chain mobility as it relates to both polymer MW and solvent swelling on these chemically- and topographically identical surfaces. Our brush films therefore displayed lower resistances to liquid drop movement with decreasing polymer MW and surface tension of probe liquid as measured by contact angle (CA) hysteresis and tilt angle measurements. Subsequently, while mobility of water drops was inferior and became worse at higher MWs, n-decane drops were found to experience little resistance to movement on these polymer brush films. Calculating CA hysteresis as Δθ(cos) = cos θ(R) - cos θ(A) (θ(A) and θ(R) are the advancing and receding CAs, respectively) rather than the standard Δθ = θ(A) - θ(R) was found to be advantageous for estimation of the actual dynamic dewetting behavior of various probe liquids on an inclined substrate.

No abstract

Extensive research on the preparation of superhydrophobic surfaces has been reported in the past decade, ranging from basic research to practical applications. Such surfaces usually exhibit water contact angles (CAs) larger than 1508. However, studies on superoleophobic surfaces, on which nonpolar (NP) liquid droplets (in particular, small volumes ca. 3-5 mL) that have appreciably low surface tensions (LSTs) can easily roll across and off, and which have a minimum tilt angle (TA) for droplet motion of less than 108, [1][2][3] are rare, despite of the practical advantages they offer. It is very challenging to fabricate surfaces that strongly promote dewetting of NP liquids, such as n-hexadecane and n-dodecane, because of their LSTs (g lv = 27.5 and 25.4 dyn cm À1 at 20 8C, respectively [4] ). When most superhydrophobic surfaces encounter such NP-LST liquids, they exhibit Wenzel wetting behavior: the liquid droplet sticks to the surface and does not roll off or dewet at any TA (poor dynamic oleophobicity). [5] Although textured surfaces with low surface energy usually maintain high advancing CAs (q A ), when the high-surface-tension (HST) liquid is replaced with a NP-LST one, receding CAs (q R ) are greatly decreased, which results in marked increases in CA hysteresis values (Dq = q A Àq R ). However, a few reports have described the formation of superoleophobic surfaces that are capable of preserving the excellent mobility of NP-LST liquid droplets. [2,3] Tuteja et al. [2] successfully fabricated perfluorinated patterned surfaces with a q A value of more than 1508 and TA = 158 for a 10 mL drop of n-octane (g lv = 21.8 dyn cm À1 at 20 8C [4] ). Zhang and Seeger [3] also prepared a superoleophobic surface consisting of CF 3 -terminated oxidized-silicone nanofilaments with topographical features similar to the "perfectly hydrophobic surface" reported by Gao and McCarthy. [6a] In that case, the minimum TAs needed for movement of 5 mL droplets of NP-LST liquids, such as n-decane (g lv = 23.8 dyn cm À1 at 20 8C [4] ) and nhexadecane, was only approximately 2-58. [3] For the prepara-tion of surfaces with such excellent dynamic oleophobicity, Zhang and Seeger [3] emphasized the necessity of producing weak interactions between the NP-LST droplets and the substrate surfaces.In contrast to such topographically modified surfaces, there have only been a few reports of flat or smooth surfaces with a low CA hysteresis value for both HST and NP-LST liquids. Proper control of both the molecular architecture (branched or ring-shaped molecules) and the physical nature of the modified surface (liquid-like surface that results from high mobility of functional groups in the surface-tethered molecules) are required to realize excellent dynamic dewetting behavior and to allow HST/NP-LST liquid droplets to easily dewet from the surface at low TAs, independent of the magnitude of the CA (this is a practical definition of "ultralyophobic"). [6b] Fadeev and McCarthy [7] and several other groups [8] have previously reported ultralyophobic ...

The effects of surface chemistry and the mobility of surface-tethered functional groups of various perfluorinated surfaces on their dewetting behavior toward polar (water) and nonpolar (n-hexadecane, n-dodecane, and n-decane) liquids were investigated. In this study, three types of common smooth perfluorinated surfaces, that is, a perfluoroalkylsilane (heptadecafluoro-1,1,2,2-tetrahydrooctyl-dimethylchlorosilane, FAS17) monomeric layer, an amorphous fluoropolymer film (Teflon AF 1600), and a perfluorinated polyether (PFPE)-terminated polymer brush film (Optool DSX), were prepared and their static/dynamic dewetting characteristics were compared. Although the apparent static contact angles (CAs) of these surfaces with all probe liquids were almost identical to each other, the ease of movement of liquid drops critically depended on the physical (solidlike or liquidlike) natures of the substrate surface. CA hysteresis and substrate tilt angles (TAs) of all probe liquids on the Optool DSX surface were found to be much lower than those of Teflon AF1600 and FAS17 surfaces due to its physical polymer chain mobility at room temperature and the resulting liquidlike nature. Only 6.0° of substrate incline was required to initiate movement for a small drop (5 μL) of n-decane, which was comparable to the reported substrate TA value (5.3°) for a superoleophobic surface (θ(S) > 160°, textured perfluorinated surface). Such unusual dynamic dewetting behavior of the Optool DSX surface was also markedly enhanced due to the significant increase in the chain mobility of PFPE by moderate heating (70 °C) of the surface, with substrate TA reducing to 3.0°. CA hysteresis and substrate TAs rather than static CAs were therefore determined to be of greater consequence for the estimation of the actual dynamic dewetting behavior of alkane probe liquids on these smooth perfluorinated surfaces. Their dynamic dewettability toward alkane liquids is in the order of Optool DSX >> Teflon AF1600 ≈ FAS17.