# Durability of Superamphiphobic Polyester Fabrics in Simulated Aerodynamic Icing Conditions
## 2 Materials and Methods
### Substrate Preparation  
Plain weave polyester fabrics (poly(ethylene terephthalate) or PET), purchased from Karstadt (Essen, Germany), were immersed in a solution of trichloromethylsiloxane (Sigma-Aldrich Chemie GmbH, Taufkirchen, Germany)(0.4 vol.%) in toluene (Fisher Scientific GmbH, Schwerte, Germany) containing water at 150 ppm, for 3 h (1-step). To increase the thickness of the coating, the solution was exchanged and replaced by a fresh solution (2-step). We refer to them as a 1-step and 2-step procedure. Upon removal from the solution, they were rinsed with n-hexane (Fisher Chemical) and dried with nitrogen. This process was used to grow a SNF network on the fabrics, making them superhydrophobic.  
Superamphiphobicity was achieved by binding fluorine groups to the surface of the SNF. Coated fabrics were activated in an oxygen plasma chamber (120 W, Femto, Diener Electronic GmbH + Co. KG, Ebhausen, Germany) for 2 min. They were then immersed in a solution of 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFDTS, 0.05 vol.%) in n-hexane for 20 min. Upon removal, they were rinsed in n-hexane and dried with nitrogen gas. The procedure has been detailed in [15; 18].  
Fluorination is necessary to make the fabric superamphiphobic, however, superhydrophobicity is sufficient for many applications. Fluorination improves the water repellency of the coating by lowering its surface energy; contact angles increase and roll-off angles decrease. For comparison, we coated the SNF with a nanometer thin PDMS film. A PDMS film reduces the surface energy of the coating, while being more environmentally friendly than fluorine. Moreover, PDMS provides the filaments with \"slippery\" properties, potentially reducing the adhesion of ice.  
To coat silicone nanofilaments with PDMS brushes, the fabrics coated with SNF were activated in an oxygen plasma (2 min, 120 W) and thereafter dipped into a solution for 15 s. The solution consisted of 0.43 mL (8.0 mmol, 1 wt.%) of sulfuric acid (H\({}_{2}\)SO4, 95%-97%) and 8.9 mL of dimethoxydimethylsilane (65 mmol, 10 wt.%) in 100 mL of 2-propanol. Prior to dipping the fabrics, the reaction mixture was stirred for 30 s and allowed to be stagnant for 30 min at room temperature. After dipping, excess solution was removed with a paper towel. The sample was then placed in a desicator for 20 min with the plasma-activated side facing upward. The humidity inside the desicator was regulated between 50% and 70% by releasing nitrogen gas, that has passed through a wash bottle containing Milli-Q water, into the desiccator. After 20 min, the sample was removed and washed with toluene, 2-propanol, and water respectively, then dried under a nitrogen stream. After coating with PDMS, the surface was superhydrophobic.  
The fabrics were imaged before and after coating by scanning electron microscopy (SEM), Figure 1. SEM images were taken using a Zeiss LEO 1530 Gemini SEM (Carl Zeiss AG, Oberkochen, Germany) at gun voltages of 3 kV with an in-lens detector. To avoid charging, samples were sputtered with 7 nm Pt using a BaITeC MED 020 modular high vacuum coating system before measurement, with an argon pressure of \(2\times 10^{-5}\) bar and a current of 30 mA (Bal-Tec AG, Balzers, Liechtenstein). The bare fibers in the fabric were smooth with frequent but random minor defects. The fabrics that were coated once (1-step) show a slightly more uniform coverage of SNF on the fibers than those coated twice. The average thickness of the coating increased from approximately 1.5 \(\upmu\)m after the first step to approximately 2.5 \(\upmu\)m after the second step. The thickness of the nanofilaments varied between 50 and 100 nm and the spacing between filaments ranged from 100 nm to 2 \(\upmu\)m (2 step). No change of the morphology could be detected after fluorination or coating with PDMS.