Design and High-Resolution Characterization of Silicon Wafer-like Omniphobic Liquid Layers Applicable to Any Substrate

Abstract

Liquid fouling can reduce the functionality of critical engineering surfaces. Recent studies have shown that minimizing contact angle hysteresis is a promising strategy for achieving omniphobic (all-liquid repellent) properties, thereby inhibiting fouling. Prior omniphobic films can repel a broad range of liquids, but the applicability of these coatings has always been limited to silicon wafers or smooth glass. Here we develop a facile procedure to generate an omniphobic coating on any surface, including metals, paper, ceramics, etc. The coating involves depositing an ultrasmooth, silicon wafer-like silica layer and then treating this layer with a highly reactive chlorosilane, which grafts polydimethylsiloxane chains onto the surface. Negligible contact angle hysteresis (≤1°) for various liquids, including ultralow surface tension oils, alcohols, and fluoro-solvents, was achieved on many different substrates regardless of their initial roughness or chemistry. In fact, the contact angle hysteresis was so low we were forced to propose an alternate measurement technique, using tilt angles, that reduced the inherent errors associated with traditional contact angle goniometry. The coating’s durability was characterized and, when it was damaged, could be repeatedly repaired, fully restoring the omniphobic properties to their initial state.

Lossless, Passive Transportation of Low Surface Tension Liquids Induced by Patterned Omniphobic Liquidlike Polymer Brushes

“…Surface Coating: The PDMS brush coating was applied following a previously reported procedure. [25] Briefly, silicon wafers were cleaned by excess toluene and isopropyl alcohol using jets from a wash bottle inside a fume hood, and dried with compressed air. They were then treated with oxygen plasma (Plasma etch PE-25) for 1 min at 106 mTorr vacuum pressure and 400 W power.…”

“…First, a layer of PDMS brushes was grafted onto the surface of a silicon wafer using vapor-phase deposition, as described elsewhere. [25] The PDMS brushes exhibited CAH < 2° with most LST liquids (Table S1, Supporting Information). Next, the desired patterns, initially wedge-shaped channels, were masked on the PDMScoated substrates (see Experimental Section).…”

Macroscopic Evidence of the Liquidlike Nature of Nanoscale Polydimethylsiloxane Brushes

“…PDMS brush surfaces exhibit excellent liquid repellency and have been described as liquidlike because the ultralow low glass transition temperature of PDMS ( T g = −125 °C) would indicate that the siloxane chains remain highly mobile and in an amorphous state at room temperature . PDMS brushes have shown excellent dynamic dewetting properties with contact angle hysteresis (CAH) below 5° for a wide range of liquids. ,,− However, a smooth, chemically homogeneous surface will inherently exhibit low CAH. For example, an ultrasmooth gold surface was reported to exhibit zero CAH with water and is clearly not liquidlike in any way.…”

“…PDMS brushes were deposited through vapor-phase deposition of chlorosilane molecules using a previously described, solvent-free method. , The covalently tethered PDMS brushes were well-characterized, and care was taken to ensure there were no free chains between the ice and silicon substrate using extensive sonication in toluene (“Methods” section). The effect of ice sliding velocity υ ice , freezing temperature T , and PDMS brush thickness t , on the ice adhesion strength τ ice was investigated.…”

Depletion of the Lubricant from Lubricant-Infused Surfaces due to an Air/Water Interface

“…These polymer brushes claim to create a liquid-like surface which, similar to the liquid layer of LIS, provide a mobile interface to reduce adhesion. 35,[41][42][43][44][45][46][47] This functionalisation is also used as a platform to stabilise lubricant. 20,22,34,35,48 Manufacture of these layers can be simple: plasma activation of glass then coating with silicone oil for at least 24 hours to form a bond between the siloxane backbone and the glass.…”