# Tuning of Morphology and Surface Properties of Porous Silicones by Chemical Modification
## 3 Results and Discussion
The apparent contact angles are summarized in Table 2. The samples exhibiting the petal effect were highly hydrophobic, with apparent CAs of around 130\({}^{\circ}\), while the sample modified with ME had a CA value of 87\({}^{\circ}\). Sample DHH, modified with hexyl groups, had a higher contact angle than DH100. The CA of sample DH70 was 151\({}^{\circ}\), which is at the limit of superhydrophobic materials. Sample DH44 exhibited the \"lotus\" effect, assigned to superhydrophobic materials with low contact angle hysteresis [21], which manifests by very low adhesion, the water droplets rolling very quickly off the surface (Supplementary Materials S3). The CA for this sample was evaluated from video captures, since the droplets rolled too quickly from the surface (estimated CAH close to 0\({}^{\circ}\)). This situation completes the wetting observations in correlation with the chemical structure, confirming that by introducing PDMS segments in large amounts, the hydrophobicity of the materials in fact increased compared with DH100, in spite of an apparently similar water uptake registered for the powder state. In this case, the water absorbed by the filter paper in the first seconds is repelled by the porous powder and cannot protrude between the particles to reach the second filter paper. Indeed, after the measurement, it was found out that the top layer of filter paper was dry to the touch in the case of all the samples in the lower region of the adsorption graph. UVME showed no surprise, having the highest water adsorption capacity, since it contains hydroxyethyl groups, which are hydrophilic. In this case, the contact angle could be calculated from the powder wettability data with the Washburn method, and the obtained value was 86.8\({}^{\circ}\), which is very close to that measured with the water drops. Superhydrophobic porous silicones with CAs over 150\({}^{\circ}\) and low sliding angles (hysteresis) have been reported [23]. The respective materials, chemically modified at the surface with perfluoroalkyl groups, were also oleophobic (CA against n-decane \(\sim\)121\({}^{\circ}\)). On the other hand, superhydrophobic and superoleophilic PDMS-MWNT sponges with very good performance in selective oil absorption have been reported [24]. The authors explained their results as a consequence of very large pores and the key role of MWCNTs being oleophilic and hydrophobic with a large surface area and a rougher surface. To our knowledge, the petal effect for highly hydrophobic porous silicones has not been reported. The morphology of the porous samples was analyzed by SEM in cross section. In most cases, open-cell pores were observed, with particularities depending on the process and composition. In the dehydrocoupling/hydrosilylation series, the morphology was in close dependency with the composition of the reaction mixture. The material obtained from neat PMHS (DH100) had large pores due to rapid H\({}_{2}\) evolution and smaller ones which are characteristic for the materials obtained by emulsion template [13] (Figure 4a). With increasing PDMS content in the DH series, the proportion of large pores (tens of micrometers) diminished at the same observation scale, along with the decrease in the cross-linking degree of the copolymers, and practically disappeared in DH30 without the PMHS precursor (Figure 4). This trend is in agreement with experimental observations of diminished foaming and prolonged cross-linking time when the proportion of PMHSdiminished. Thus, the emulsion template had an increasing role in tuning the pore size. The generation of large pores in dehydrocooupling increased the interconnectivity of the structures, since the small pores are practically windows in the open cells; thus, hierarchical structures formed. When the PMHS was modified with ATMS, the morphology looked like a fine lace: very small pores formed almost exclusively (Figure 4e). Due to the small size, the interconnectivity of the pores could not be clearly observed in all samples.