# Tuning of Morphology and Surface Properties of Porous Silicones by Chemical Modification
## 1 Introduction
When CAH values are very high, the water drops are pinned on the surface, like in the case of rose petals [21]. Silicones are inherently hydrophobic materials, providing low energy surfaces. Superhydrophobicity can be achieved by chemical modification of silica films or by creating micro-/nanostructures from PDMS using lithography, templates, or chemical reactions, as recently reviewed [22]. For example, a superhydrophobic and oleophobic silicone sponge with hierarchical structures was obtained by introducing a secondary structure on the pore walls of a hydrophobic and oleophilic silicone sponge [23]. Superhydrophobic and superoleophilic behavior was reported for PDMS-MWCNT porous composites, based on the combination of methyl groups on the surface of PDMS and increased surface roughness due to MWCNTs [24]. However, apart from a few exceptions, the literature on porous silicones rarely addresses the surface properties in correlation with chemical structure. On the one hand, assessing the surface properties of porous materials may be challenging, and on the other hand, most porous silicones are designed for specific applications and emphasis is given to their performance. Also, in most articles, the basic materials are commercially available silicone kits, and parameters other than composition or chemical structure are followed. In our previous report, the emulsion template method was adapted based on a pair of siloxane surfactants soluble in water and in toluene, respectively, and used to obtain porous silicones [13]. In this method, the continuous phase is a solution of silicones in toluene, and the disperse phase is water. The pores are formed by rapid UV-initiated thiol-ene photoaddition reaction, which ensures the cross-linking of the vinyl-containing silicone precursor, followed by the solvent's evaporation. Herein, the emulsion template method was combined with the dehydrocoupling reaction and chemical modification in order to obtain silicone materials with tunable morphology and surface properties. First, PMHS was cross-linked in emulsion with a Pt catalyst without other additions. Then, the composition of the reaction precursors was varied in order to introduce PDMS segments and lower the cross-linking density. Next, the PMHS was chemically modified in situ with n-hexane or allytrimethylsilane, aiming to obtain porous materials with increased hydrophobic behavior. In another series, a dimethyl-methylvinyl siloxane copolymer was cross-linked by thiol-ene photoaddition and chemically modified in situ with mercaptoethanol to induce hydrophilic behavior. The resultant materials were investigated in powder state by performing tensiometry wetting measurements, and the obtained results were correlated with qualitative observations and contact angle measurements. Depending on the chemical structure and morphology, the wetting behavior of these materials can span from hydrophilic to superhydrophobic, with \"lotus\" or \"petal\" effects. As a consequence, a large diversity of related materials can be obtained by very simple and mild methods, with applications spanning from the sorption of organic compounds to self-cleaning. In particular, the petal effect, observed on three of our samples, and which has rarely been reported in the case of porous silicenes, is considered interesting for applications, such as single-molecule spectroscopy and controlled transport of small volumes of liquid in open microfluidic devices [25].