# Preparation and Application of ZIF-8 Thin Layers
## 3 Results
### Wetting Properties  
The wetting properties of the ZIF-8 layers were assessed via contact angle measurements. The results are shown in Table 2. Measurements on a PVDF layer and on a HKUST-1 layer (values taken from [33]) are included for comparison. The results show that oil infusion with GPL 105 leads to a low contact angle hysteresis for both water and diiodomethane. Untreated ZIF-8 layers show high advancing contact angles, but the droplets are pinned to the surface so that the receding contact angles for water and diiodomethane could not be measured accurately. This is most likely due to the roughness of the highly porous ZIF-8 layers. Oil infusion with GPL 100 shows lower advancing contact angles than the untreated surfaces, but the droplets are also pinned to the surface. GPL 100 has a much lower viscosity than GPL 105 (20 cP vs. 800 cP at room temperature [42]). The higher viscosity of GPL 105 seems to result in a smoother oil surface, while after infusion with GPL 100, the surface roughness still has a considerable effect on the wetting properties. The variation of PVDF fraction in the ZIF-8 layers does not show any considerable effect on the advancing or receding contact angles. The wetting properties of the ZIF-8/PVDF (20%) monolayer are similar to the corresponding double layer. The ZIF-8 e-coating shows higher water contact angle hysteresis. This is most likely due to the higher roughness of the e-coating compared to the surfaces fabricated with the doctor-blade technique. Compared to the values of HKUST-1 taken from the literature [33], a considerably smaller contact angle hysteresis was achieved with the ZIF-8 layers. Considering all the contact measurements, the fluid properties of the oil and the roughness of the base surface structure are the key  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sample** & \(R_{d}\)**/**nm** & \(R_{d}\)**/**nm** & \(R_{p}\)**/**nm** & \(R_{e}\)**/**nm** &
\begin{tabular}{c} **Scan** \\ **Length/mm** \\ \end{tabular} \\ \hline PVDF & 0.415 \(\pm\) 0.00 & 0.522 \(\pm\) 0.01 & 2.417 \(\pm\) 0.06 & 1.953 \(\pm\) 0.03 & 0.75 \\ \hline ZIF-8/ & & & & & \\ PVDF (40\%) & 0.895 \(\pm\) 0.05 & 1.245 \(\pm\) 0.09 & 6.561 \(\pm\) 1.21 & 5.159 \(\pm\) 0.34 & 0.75 \\ \hline ZIF-8/ & & & & & \\ PVDF (20\%) & 0.568 \(\pm\) 0.04 & 0.780 \(\pm\) 0.05 & 4.146 \(\pm\) 0.35 & 3.130 \(\pm\) 0.29 & 0.75 \\ \hline ZIF-8/ & & & & & \\ PVDF (10\%) & 0.510 \(\pm\) 0.05 & 0.661 \(\pm\) 0.07 & 5.655 \(\pm\) 2.25 & 4.273 \(\pm\) 1.09 & 0.75 \\ \hline ZIF-8 & & & & & \\ (e-coating) & 3.411 \(\pm\) 0.45 & 4.386 \(\pm\) 0.63 & 61.990 \(\pm\) 29.77 & 15.164 \(\pm\) 2.99 & 0.75 \\ \hline HKUST-1 [33] & & & & & \\ (e-coating) * & 2.233 \(\pm\) 0.23 & 2.780 \(\pm\) 0.26 & 11.097 \(\pm\) 0.70 & 9.037 \(\pm\) 0.70 & 1 \\ \hline \hline \end{tabular}  
* Roughness parameters were measured in one dimension instead of two dimensions for the ZIF-8 and PVDF layers.  
\end{table}
Table 1: Surface roughness parameters—\(R_{a}\): arithmetical average roughness, \(R_{q}\): root mean square roughness, \(R_{p}\): maximum peak height, \(R_{p}\): maximum valley depth for ZIF-8 and PVDF layers. The parameters for HKUST-1 were taken from ref. [33] and included for comparison.  
parameters that define the wetting properties of the resulting oil-infused surface, while the surface chemistry of the base material has a little influence.