Polydimethylsiloxane‐Silane Synergy enables Dropwise Condensation of Low Surface Tension Liquids

Abstract

Despite decades of research on promoting the dropwise condensation of steam, achieving dropwise condensation of low surface tension liquids remains a challenge. The few coatings reported to promote dropwise condensation of low surface tension liquids either require complex fabrication methods, are substrate dependent or have poor scalability. Here, the rational development of a coating, which is applicable to all conventionally used condenser metals, is presented by combining a low contact angle hysteresis polydimethylsiloxane with a low surface energy silane using atmospheric vapor phase deposition. The siloxane-silane coating enables the dropwise condensation of fluids with surface tensions as low as 15 mN m −1 in pure vapor conditions. This siloxane-silane coating enables a 274%, 347%, and 636% heat transfer enhancement during ethanol, hexane, and pentane condensation, respectively, when compared to filmwise condensation on the same un-coated surfaces. Furthermore, this coating exhibits 15 days of steady dropwise condensation with no apparent signs of coating degradation. This study not only demonstrates the possibility of achieving stable dropwise condensation of low surface tension fluids on scalable, structure-less surfaces, it also develops design principles for creating facile, substrate-independent, durable, and scalable omniphobic coatings for a plethora of applications.

Advances in micro and nanoengineered surfaces for enhancing boiling and condensation heat transfer: a review

“…Very few surface modification techniques have succeeded in achieving scalable and sustainable dropwise condensation of low surface tension liquids. 234–236 Studies on lubricant infused structured surfaces (LIS) have introduced the methodology of modifying micro and nanostructured surfaces with lubricant infusion for enabling enhanced condensation of liquids. 230,237–239 Lubricant infused nanostructured surfaces have successfully been implemented to achieve stable dropwise condensation of toluene, ethanol, hexane, and pentane which are low surface tension fluids (Fig.…”

Sprayable Superoleophobic Coatings for Pumpless Handling of Low‐Surface‐Tension Liquids

“…In recent work, researchers have prepared a siloxane‐silane coated surface using chemical vapor deposition (CVD) to enhance the dropwise condensation of low‐surface‐tension liquids. [ 44 ] Although the coating successfully reduced the contact angle hysteresis and enabled dropwise condensation, the surfaces remained oleophilic (contact angles well below 90°). To fabricate surfaces that can successfully repel low‐surface‐tension liquids, researchers have shown that specially designed re‐entrant structures are required to prevent the liquid from spreading.…”

Durable, Ultrathin, and Antifouling Polymer Brush Coating for Efficient Condensation Heat Transfer

“…It can lead to a significantly high thermal resistance of more than 10 –5 m 2 ·K·W – 1 on a copper substrate, − compromising the heat transfer benefits from the dropwise condensation mode. To reduce the thermal resistance, ultrathin polymer brushes (ideally at the nanoscale level), such as polydimethylsiloxane (PDMS) brushes, − can be grafted onto the metal substrate. The coatings are ultrathin (∼6 nm) with low thermal resistance (<10 –7 m 2 ·K·W – 1 , Figure S1, Supporting Information) and able to repel water drops with low contact angle hysteresis (<10°).…”