Design of Highly Oleophobic Cellulose Surfaces from Structured Silicon Templates

Abstract

Structured silicon surfaces, possessing hierarchical porous characteristics consisting of micrometer-sized cavities superimposed upon a network of nanometer-sized pillars or wires, have been fabricated by a plasma-etching process. These surfaces have superoleophobic properties, after being coated with fluorinated organic trichlorosilanes, on intrinsically oleophilic surfaces. By comparison with flat silicon surfaces, which are oleophilic, it has been demonstrated that a combination of low surface energy and the structured features of the plasma-etched surface is essential to prevent oil from penetrating the surface cavities and thus induce the observed macroscopic superoleophobic phenomena with very low contact-angle hysteresis and low roll-off angles. The structured silicon surfaces were coated with cellulose nanocrystals using the polyelectrolyte multilayer technique. The cellulose surfaces prepared in this way were then coated with a monolayer of fluorinated trichlorosilanes. These porous cellulose films displayed highly nonwetting properties against a number of liquids with low surface tension, including alkanes such as hexadecane and decane. The wettability and chemical composition of the cellulose/silicon surfaces were characterized with contact-angle goniometry and X-ray photoelectron spectroscopy, respectively. The nano/microtexture features of the cellulose/silicon surfaces were also studied with field-emission scanning electron microscopy. The highly oleophobic structured cellulose surfaces are very interesting model surfaces for the development of biomimetic self-cleaning surfaces in a vast array of products, including green constructions, packaging materials, protection against environmental fouling, sports, and outdoor clothing, and microfluidic systems.

Superamphiphobic surfaces

“…In the Wenzel regime (Fig. 2b), the difference of the measured  CA from the 'true' contact angle of a flat surface ( F ) was described as follows: 40 where R is the ratio between the actual surface area of the rough surface and the apparent area. In this regime, surface roughness can promote either wettability ( CA < 90°) or non-wettability ( CA > 90°), depending on the chemical property of the surface.…”

“…26 27 demonstrated that superamphiphobic surface could be obtained perfluorosilanerendered TiO 2 /single-walled carbon nanotube composite coatings. Interestingly, the wetting ability of such coatings could be tuned from superoleophobic to superoleophilic via ultraviolet 40 irradiation. Moreover, by controlling the dose of UV illumination, superphobicity and superphilicity can exist on the same surface for probing liquids with different surface tensions.…”

“…38 Glass can be 10 tailored by ion etching, and subsequently chemical etching in aqueous HF. 39 Besides the etching techniques discussed above, other etching methods such as plasma etching 40 and water etching 41 can also be applied, depending on the chemical property of the substrate. …”

“…35 Scale bar = 20 m. However, it remains a challenge to create superoleophobic surfaces that resist wetting for organic liquids because of their 40 low surface tensions, for example, 23.8 mN•m -1 for decane, which are much lower than that of water (72.3 mN•m -1 ). To the best of our knowledge, superoleophobic surface was first developed through the design of re-entrant surface curvature, in conjunction with chemical composition and roughened texture 45 surface, by Tuteja et al in 2007.…”

“…A syringe pump is used to generate a water droplet on the substrate, and to control the rate of water pumping and suction through the needle to 40 perform the advancing and receding, respectively. After the dropforming step, water is continuously and slowly pumped into (or sucked from) the droplet at a rate smaller than 0.3 ml•min −1 and  Adv was recorded simultaneously by a frame grabber via a solid state charge coupled device camera (Fig.…”