Attension theta lite 100

Schottky field emission scanning electron microscope (SEM, Zeiss Supra 55VP, Carl Zeiss AG, Jena, Germany) was used for morphology evaluation. The samples were dried in ambient air for 24 h, then immersed in liquid nitrogen and cut. The samples were coated by Balzers sputter coater (SCD 050, BAL-TEC, Oerlikon Balzers, Bergisch Gladbach, Germany) with a thin film of carbon before SEM imaging. The contact angles of the samples were measured by optical tensiometer (Attension Theta Lite 100, Biolin Scientific, Espoo, Finland). Three to five measurements were recorded for the average value. A digital micrometer (293–330 Mitutoyo, Kawasaki, Japan) was used for sample thicknesses measurement. Porosity (ε) of the membrane samples was measured by determining the net wet (W₁) and dry mass (W₂) based on the following equation [41 (link)]: $$\epsilon =\frac{\left(W_1-W_2\right)/{\rho }_i}{\left[\frac{W_1-W_2}{{\rho }_i}\right] +\left[W_2/{\rho }_m\right]} \times 100$$
where $${\rho }_i$$ and $${\rho }_m$$ are the density of the solvent and membrane, respectively.
Membrane tensile strength was obtained by an LS₁ tensile testing device (AMETEK, Lloyd Instruments, Ltd., UK). The structural parameter (S value) of the membrane was calculated by the following equation by considering membrane tortuosity ( $$\tau$$ ), porosity (ε), and support layer thickness ( $$t$$ ): $$S=\frac{t\tau }{\epsilon }$$