Synergistic Effect of Dual Ionic Liquid PVDF‑HFP Polymer Inclusion Membranes: Linking Mechanical, Chemical, Microstructural and Gold Recovery Performance

Abstract

Poly (vinylidene fluoride‑co‑hexafluoropropylene) (PVDF‑HFP) polymer inclusion membranes (PIMs) are widely used across separation industries because of their ability to selectively separate ions or molecules, their chemical stability, and their mechanical flexibility. Still, improving how the membrane performs without making the membrane material properties deteriorate remains a challenge. In this study, Aliquat 336 and Cyphos IL 104 were blended with PVDF‑HFP and fabricated through the solvent casting method. The main objective of this study is to understand how the ionic liquids can affect the membrane’s chemical properties, physical properties, mechanical stability, and its ability to recover gold through an H-cell setup.  FTIR analysis confirmed the presence of Aliquat 336, showing bands associated with quaternary ammonium groups, while Cyphos IL 104 displayed vibrations related to phosphonium‑related P–C. SEM images further revealed clear differences in how the membrane morphology looked. Pure PVDF-HFP alone had compact surfaces; Aliquat 336 membranes appeared to have smoother features, and Cyphos IL 104 membranes developed rougher surfaces with micro-voids. The addition of ionic liquids also increased membrane porosity from 25 % in the pure membrane to 45 % with the addition of ionic liquids. At the same time, the contact angle dropped from 90° to 58°, indicating improved hydrophilicity. Mechanical testing showed that pure PVDF‑HFP had the highest tensile strength (30 MPa), modulus (450 MPa), and tear resistance (2.5 N/mm). Membranes with higher Aliquat 336 content retained better tear resistance, close to 2.0 N/mm, while maintaining smoother membrane surfaces. In comparison, the addition of Cyphos IL 104 adversely impacts the mechanical properties. Gold extraction experiments showed promising performance. The PVDF-HFP/A15C20 membrane achieved 76 % recovery within 12 h. The combination of both Aliquat 336 and Cyphos IL 104 improved ion transport while maintaining acceptable membrane stability properties. Overall, the results showed that the ionic liquid composition has a strong influence on both the membrane’s durability properties and separation performance. These findings provide a useful approach for developing membranes in precious metal recovery applications.