Comparing methods for preparing slippery liquid-like polydimethylsiloxane coatings

Slippery covalently attached liquid surfaces (SCALS, also called quasi-liquid surfaces, liquid-like surfaces and slippery omniphobic covalently attached surfaces) have recently emerged as a new family of materials with many useful properties such as droplet-shedding, deicing and antifouling. They can also serve as model systems in studies of wetting, evaporation and self-assembly phenomena. They are made of nano-thin layers of polymers or oligomers that are liquid at ambient temperature and covalently attached to a smooth substrate. Here we lay out procedures for preparation of the most common SCALS system: polydimethylsiloxane bound to silica surfaces via silane chemistry. The apparent simplicity of these layers and their methods of preparation is misleading, and obtaining reproducible results requires careful control of the reaction parameters. The exact details of the synthetic methods for SCALS determine the observed results; it is therefore essential to report both the synthetic detail and the characterization results to improve reproducibility and to advance understanding of the field. Here a range of synthetic methods used in the literature were reproduced in three different laboratories across the world, their comparative advantages and disadvantages discussed and the resulting SCALS characterized. For each synthetic method, the key parameters that contribute to their performance and ease of reproducibility were identified and optimized.