Substrate-independent, robust and functional PVDF-g-IL coating based on tunable surface free energy

Abstract

Substrate-independent and robust coatings with desired functions are highly demanded in many fields. The fabrication and fundamental theory of them, however, remain challenging for decades. Herein, we aim to elaborate it from a new perspective, in which the challenge has been attributed to the different or even conflicting requirements on surface free energy (SFE) at substrate/coating (bottom) and coating/air (top) interfaces. In this work, a novel strategy has been developed to tailor SFE continuously and reversibly based on counterion exchange. Polyvinylidene fluoride grafted with ionic liquids (PVDF-g-IL) coating with hierarchical surface roughness was fabricated via solution casting and vapor induced phase separation. In the as-prepared specimen, the surface free energy was calculated based on Neumann method. The resultant high SFE (from the counterion of [Cl−] and hierarchical roughness) contributes to the superior bondability of coating/substrate, corresponding to the excellent universality and robustness of PVDF-g-IL coating assessed via T-peeling test. After that, controlled counterion exchange between [Cl−] and [PFO−] (pentadecafluorooctanate anion) has been employed to tailor SFE at top interface. The consequent high/low magnitudes of SFE enable the super-hydrophilic/super-hydrophobic properties at solid/liquid interface while the tunable SFE dominates serial adsorption at multiple-phase interface.