3.3.1. Hydrophobic Coating and Characterization of Different Material SurfacesOnce the polymeric materials were prepared and characterized, the first coating experiments were carried out by immersing 1.5 × 1.5 cm glass slides, previously cleaned with plasma (400 W, 5 min), in a ~7 mM CH2Cl2 solution of P4b overnight, without stirring. After this period, the substrates were removed from the solution and dried in a gentle flux of argon. The wettability of such surfaces was evaluated from WCA measurements, using Milli-Q water droplets (ca. 5 µL) by means of the sessile-drop technique. These measurements showed a contact-angle value of 95° (5° for the pristine glass). It is worth mentioning that the P4b robustness was challenged with intensive cleaning three times, with fresh CH2Cl2, in which the oligomer is soluble, in the presence of ultrasounds. After such a strong cleaning process, the substrate extraordinarily still retained a hydrophobic character, with a contact-angle close to 80°. For this reason, and to reinforce the viability of our approach, from now on all the substrates of this work were cleaned under these drastic conditions. For comparison purposes, the same procedure was now repeated using the precursor monomer 4b, previous polymerization. In this case, even though the initial WCA value was relatively high (84°), it immediately dropped down to 55°, confirming that the monomer self-assembly coatings are less stable (for more information about the coating-procedure see Supporting Information S7).AFM surface-topography imaging of a standard P4b glass coating in ambient (air) conditions revealed a consistent average thickness of 1.5 µm and a roughness of 435 ± 32 nm, as measured upon scratching a section of the substrate (see Figure 1b). Other experimental factors such as substrate orientation and time evolution were also studied. For this, four cleaned glass-slides were submerged in a P4b HPLC-grade CH2Cl2 solution for 1 h, 4 h, 8 h, and overnight. Afterwards, they were washed three times with fresh CH2Cl2, dried in a gentle flux of argon, and the WCA was measured. It is worth mentioning that the WCA values after 4 h were comparable with the ones obtained after 8 h, or even overnight (the WCA values ranged between 71° and 76° in all cases). Therefore, and since it is the shortest experimental time used, experiments at 4 h were now repeated, depositing the slides into the solution with two different orientations, one lying on the bottom of the vial (parallel) and the second one resting on the wall (perpendicular). Afterwards, they were washed with fresh CH2Cl2, and dried with a flux of argon, resulting in comparable hydrophobic values (73° vs. 76°, respectively).Beyond the glass, three additional surfaces (aluminum, copper, and stainless steel), were also studied, for comparison purposes. As a general procedure, 1.5 × 1.5 cm slides were cleaned by sonicating in acetone, EtOH 96% and Milli-Q water for 10 min, and dried in a gentle flux of argon. Afterwards, coating with P4b was achieved, following the same formula used for the glass surfaces, and characterized by EDX, showing in all cases signals around 2.3 KeV, characteristic of sulphur atoms (see Supporting Information, S8). Furthermore, carbon and oxygen were also identified, and the measured percentages of these were around the expected ones (±10%).Afterwards, the WCAs were measured, and from there, two main deductions can be extracted (Figure 1). First, in all the cases our coating clearly improves the hydrophobic character, even if the pristine material already exhibits considerable WCA values (see Figure 1a). Second, the WCA differences before and after washing are even less remarkable than for glass, endorsing the robustness of our coating. In fact, once more, coating of the three substrates with the styrene derivative P6b revealed WCA values remarkably reduced, in comparison with P4b, except for copper substrates, most likely due to the affinity of unreacted terminal thiol-groups for this material. Finally, and regardless of the surface, no color modification was detected upon coating.

The polymerization protocol was also tested in situ. For this, the four substrates (including glass) were initially coated by submerging them in a ~7 mM CH2Cl2 solution of 4b, and afterwards placing them on closed vials overnight with iodine, ensuring sublimation. Afterwards, surfaces were washed three times with fresh EtOH 96% to remove the excess of iodine, and dried in a gentle flux of argon. At first sight, the area in contact with iodine had already become scattered, pointing to a polymerization reaction. Accordingly, in all cases there was a considerable increase of WCA values, compared with the corresponding blanks (iodine sublimation in the absence of the P4b coating), and even for the corresponding coating obtained in solution. This did not apply for aluminum and especially stainless-steel, a fact attributed to the iodine effects (the direct interaction of stainless steel with iodine reduces its WCA from 44° to 12°). An EDX analysis of all samples showed the presence of sulphur at 2.3 keV, carbon at 0.27 keV, and oxygen at 0.52 keV.

3.3.3. Oil-Absorbance and Oil/Water-Separation Experiments with Hydrophobic Coated Cotton-TextileBecause of its remarkable water-repellent performance, P4b-coated textiles were then used for oil-absorbance tests and oil/water-separation experiments, simulating the removal of oily pollutants from aqueous phases. Two oily phases, tetradecane (TDC) and olive oil, colored with Disperse red 13, were used as non-volatile model pollutants upon the addition of 15 mL of distilled water. Afterwards, P4b-coated cotton fibers of known weight (dry) were soaked in the oil phase for 15 s, taken out, allowed to drain for 3 h, and weighted again. The coated fibers showed a 127% weight increase with TDC (25% for pristine cotton), and a 172% weight increase with olive oil (94% for pristine cotton). In accordance with this, SEM images of the fibers before and after absorbing TDC and olive oil reveal differences. A piece (1 × 2 cm) of [email protected]P4b was also placed on top of a 20 mL vial, and used as a filter for phase separation of a Miglyol® 840 colored with a red-Disperse-13 and distilled-water mixture (1:1). Immediately after deposition with a syringe, oil quickly saturated the coated-cotton passing through, while water was retained at the top. Another piece of [email protected]P4b (1 × 1 cm) was also successfully used to recover a microemulsion (20 µm average droplet-size) of Miglyol® 840 colored with Disperse red 13 in water stabilized with sodium dodecyl sulfate (SDS). For this, the textile was submerged in a 10× diluted aliquot of the stock emulsion, gently stirred by hand for 5 min, and subsequently taken out of the treated emulsion and left to dry in air. The coated cotton absorbed up to 97% of its own weight, and therefore acquired a remarkable red color, whereas the weight increase for the uncoated cotton was only 8% (Figure 2).