Easydrop

The hydrophilicity of the membrane surface was represented by contact angle that was measured using Kruss GmbH FNY12MKE Easy Drop, Germany under ambient conditions. Fourier-transform infrared spectroscopy (FTIR) analysis was conducted using a Nicolet 6700 Thermo Scientific-FITR spectrometer (United States) to identify the functional groups present on the membrane. Membrane surface zeta potential was measured using the Malvern Surface Zeta Potential Cell, Malvern Instruments, UK. The zeta potential of membrane surface was measured in 0.1 mM NaCl at pH 7 using 300–350 nm latex particles as the tracer particles (DTS1235 Malvern UK).
The overall membrane porosity (ε) was calculated using the gravimetric method^{29 (link)}, as defined in Equation (1): $$\epsilon =\frac{{\omega }_1-{\omega }_2}{A\times l\times d_w}$$ where ω₁ is the wet membrane weight (g), ω₂ is the dried membrane weight (g), A is the membrane surface area (m²), l is the membrane thickness (m), and d_w is the water density (998 kg/m³).
Using the porosity data and Guerout–Elford–Ferry equation^{35 (link),36 (link)}, the relative pore sizes of the fabricated membranes were calculated using Equation (2): $$r_m=\sqrt{\frac{\left(2.9-1.75\epsilon \right)8\eta lQ}{\epsilon \times A\times \mathrm{\Delta }P}}$$ where η is the water viscosity (8.9 × 10⁻⁴ Pa.s), Q is the volume of pure water permeated through the membrane per unit time (m³/s), and ΔP is the operational pressure (0.4 MPa).

The dispersive
(γ_S^d)
and polar (γ_S^p) surface energies of PET and PP were determined from the
contact angle of various test liquids (see Table S1 of the Supporting Information) on film samples using sessile
drop method (EasyDrop, Krüss GmbH, Hamburg, Germany). Prior
to the measurement, PET and PP were hot-pressed (4122 CE, Carver Inc.,
Wabach, USA) at 240 and 190 °C, respectively, under a weight
of 2 tons to produce polymer films of ∼0.3 mm in thickness.
The polymer film was then affixed on a glass slide using double-sided
tape. A liquid droplet of 10 μL was carefully deposited on the
surface of the polymer film, and the sessile drop was analyzed using
the ellipse fitting method (Krüss ADVANCE, version 1.9.0.8).
An average of five measurements was taken for each type of test liquid.
The γ_S^d and γ_S^p of PET and PP were calculated using the Owen–Wendt–Rabel–Kaelble
(OWRK) approach.^{31 (link)}

The surface topography of the R-ST was measured by atomic force microscopy (AFM; NX10, Park Systems Co., Suwon, Korea), followed by image analysis using XEI Software (Park Systems Co.). Water contact angle analysis was carried out by a contact angle goniometer (EasyDrop, model FM40Mk2, Krüss, Hamburg, Germany) using a drop-shape analysis program. Raman and X-ray photoelectron spectra (XPS) of samples were collected using Raman spectrometer (Micro Raman PL Mapping System, Dongwoo Optron Co., Ltd., Gwangju, Korea) and x-ray photoelectron spectrometer (AXIS Supra, Kratos Analytical, UK), respectively. The base pressure in the XPS chamber was 5 × 10^− 10 mbar. A wide scan was performed correcting the binding energies with C 1 s as reference energy (C 1 s = 284.8 eV). Fourier transform infrared (FTIR) spectra were collected by an FTIR spectrophotometer (Nicolet 560, Nicolet Co., Madison, WI). All spectra were recorded in absorption mode in the wavelength range of 1000-4000 cm^− 1 with a resolution of 4.0 cm^− 1 and 16-times scanning. Electron backscattered diffraction (EBSD) analysis was carried out by using the TEAM™ EBSD Analysis System combined with energy-dispersive X-ray (EDAX) to evaluate the texture and grain size of the samples setting the voltage at 20 kV and current at 6.0 nA.