## 2 Materials and Methods
### Membrane Distillation Setup  
The membrane distillation performance was evaluated with a lab-scale DCMD setup (Figure 6). The flat-sheet module had a feed and permeate channel with dimensions of 6 cm width and 18 cm length. The channel height and spacer thickness was 2 mm. On the permeate side, purified water with electrical conductivity below 20 \(\upmu\)S\(\cdot\)cm\({}^{-1}\) was used. The feed and distillate were circulated counter-currently on their respective sides of the membrane with a flow velocity of 0.13 m/s using peristaltic pumps (Watson-Marlow, 520 DuN/R2, Zwijnaarde, Belgium). \(T_{f,in}\) and \(T_{p,out}\) was kept constant at 60 \({}^{\circ}\)C and 45 \({}^{\circ}\)C, respectively, for all experiments. The temperatures were kept constant using two heating baths ([PERSON], Ministat 230w-cc-NR, Offenburg, Germany) and monitored using four thermocouples (Thermo Electric Company, PT100 TF, Balen, Belgium). The flux was measured by evaluating the weight variations in the feed and distillate tank, using an analytical balance (Sartorius GmbH, ED8801-CW, Goettingen, Germany). The average of at least two experiments \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Coating** & **Coating Components** & **Mass Fraction in Coating Solution** & **Application Method** & **Network Formation** \\ \hline
1 & PFD solution & 5 wt. \% & Roll-to-roll system & No organic crosslinking \\
2 & PFD solution & 10 wt. \% & Roll-to-roll system & No organic crosslinking \\
3 & Ak/T/D/BTFO2N & 5 wt. \% & Bar coater & Acrylic polymerization \\
4 & Ak/T/D/BTFO2N & 30 wt. \% & Roll-to-roll system & Acrylic polymerization \\
5 & V/Mc/F13 & 5 wt. \% & Bar coater & Vinyl + SH addition \\
6 & V/Mc/F13 & 5 wt. \% & Spray coater & Vinyl + SH addition \\
7 & V/Mc/F13 & 5 wt. \% & Spray coater & Vinyl + SH addition \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Composition of the coatings used in this study (perfluorodecyl: PFD; the second system: Ak/T/D/BTFO2N; the third system: V/Mc/F13). is reported. The electrical conductivity at the feed and permeate side were monitored by portable conductivity meters (WTW GmbH, pH/Cond 340i, Weilheim, Germany). The energy efficiency (\(EE\)) of the process is defined in Equation (3). The total heat transfer through the membrane \(Q_{m}\) is considered to be equal to the heat transfer in the feed channel, as described by [PERSON] et al. [45]. \[EE\ (\%)\ =\ \ \ \frac{N\cdot\Delta H\cdot A}{F\cdot C_{p}\cdot(T_{in}\ -\ T_{out})} \tag{3}\]  
\(N\) (kg\(\cdot\)m\({}^{-2}\).h\({}^{-1}\)) is the water flux and \(\Delta H\) (J\(\cdot\)kg\({}^{-1}\)) the enthalpy of evaporation. \(F\) is the mass flow rate in the channels expressed in kg\(\cdot\)s\({}^{-1}\), \(A\) (m\({}^{2}\)) is the effective membrane surface area, \(C_{p}\) is the specific heat capacity of the solution (J\(\cdot\)kg\({}^{-1}\cdot\)\({}^{\circ}\)C\({}^{-1}\)), \(T_{in}\) and \(T_{out}\) are the bulk temperatures at the channel inlet and outlet of the module expressed in \({}^{\circ}\)C, respectively. The calculations were carried out for the feed and permeate channel and the average and standard deviation are reported. Long term stability tests were performed using 35 g\(\cdot\)L\({}^{-1}\) NaCl as feed concentration. The experimental conditions were chosen differently from the screening tests, because these experiments run overnight. The flux should be limited, to prevent spilling over of the permeate vessel. Therefore, lower temperatures have been chosen for these experiments: \(T_{f}\) and \(T_{p}\) were 45 \({}^{\circ}\)C and 40 \({}^{\circ}\)C respectively with a cross flow velocity of the feed of 0.1 m\(\cdot\)s\({}^{-1}\) and a salinity of 35 g\(\cdot\)L\({}^{-1}\). The goal of this experiment was mainly to investigate the stability of the coating under constant shear of the feed liquid, not the thermal stability. In general, the thermal stability of the hybrid coatings is 150 \({}^{\circ}\)C and higher, up to 300 \({}^{\circ}\)C. This thermal stability has been measured for another application elsewhere [4].