Experimental data for “Fabrication and Anti-wetting Enhancement mechanism studying of the PVDF Membrane with a Porous-Dense Asymmetric Structure for Enrichment of Salt Lake Brine”

The microstructure of the membranes was examined using scanning electron microscopy (SEM) to analyze fiber diameter distribution, fiber orientation, pore structure, and fiber interlacing. SEM observations were performed with a field-emission scanning electron microscope (FE-SEM, SU8010, Hitachi, Japan / Oxford Instruments). Prior to imaging, the membrane samples were sputter-coated with a thin layer of gold to improve conductivity. Fiber diameters were measured using ImageJ software, with at least 100 randomly selected fibers per sample to ensure statistically meaningful results. Additionally, energy-dispersive X-ray spectroscopy (EDS) coupled with SEM was employed to determine the elemental composition and distribution of the membranes. EDS measurements were conducted at an accelerating voltage of 10–15 kV, with a focus on C, F, Na, Cl, and O elements, in order to verify distribution of element on the surface of membranes before and after MD processes. The surface wettability of the membranes was evaluated using a contact angle measurement system (Krüss DSA25S). Deionized water was used as the probe liquid, and static water contact angles were measured at room temperature with a droplet volume of 2–3 μL. Each sample was measured at no fewer than three different locations, and the average value was reported. The molecular structure and crystalline phase composition of the PVDF membranes were analyzed by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD). FTIR measurements were conducted using a Fourier Transform Infrared spectrometer (iS50, Thermo Fisher Scientific, USA) over a wavenumber range of 4000–500 cm⁻¹, with a resolution of 4 cm⁻¹ and 32 scans per spectrum. Characteristic absorption peaks were used to identify the presence and relative content of different PVDF crystalline phases (α, β, and γ), reflecting the molecular chain conformation. XRD analysis was performed using an X-ray diffractometer (D8 Discover, Bruker, Germany) with Cu Kα radiation (λ = 1.5406 Å) at an operating voltage of 40 kV and a current of 40 mA. Diffraction patterns were collected over a 2θ range of 10°–60° at a scanning rate of 2°·min⁻¹. The relative contents of α, β, and γ crystalline phases were quantitatively analyzed to elucidate the crystalline structure characteristics of the membranes.Direct-contact membrane distillation (DCMD) was employed to evaluate the performance of the prepared membranes. The DCMD setup consisted of a flat-sheet DCMD module with an effective membrane area of 32 cm². The feed solution was heated to 80 °C using a 350 W electric heating rod and continuously circulated at a flow rate of 0.35 L·min⁻¹ by a peristaltic pump. On the permeate side, deionized water with a conductivity below 1 μS·cm⁻¹ was used as the coolant and maintained at 20 °C by a 400 W cooling unit, with a circulation flow rate of 0.35 L·min⁻¹. The low-salinity solution (3.5 wt%) was utilized as the feeding solution to optimize the electrospinning fabrication parameters and to investigate the mass transfer behavior during membrane distillation, whereas the high-salinity solution (10 wt%) was applied to assess the desalination performance and long-term operational stability of the membranes under high-salinity conditions. For all DCMD experiments, the initial working volume of both the feed and permeate reservoirs was fixed at 2.0 L.