Construction And Evaluation Of Surface Free Energy Model Based On PVDF-g-IL Coating

Surface features of material are closely related to the wettability,adhesion,adsorption,biocompatibility and other properties.In practice,coating techniques have been widely employed to achieve these functions and attract both scientific and industrial interests.To attain durable coatings with certain function,one must carefully address two interfaces,i.e.,the bottom interface where the coating meets substrate and the top interface(i.e.,surface)where the coating is exposed to air.From the view of surface free energy(SFE),the requirements at two interfaces of coating are of great difference.At bottom interface,high SFE of coating is always demanded since it facilitates the adhesion between coating and substrate which is the key for its universality and long-term stability.The requirement on SFE at coating surface,however,depends crucially on application scenarios.The different or even conflicting requirements on SFE at two interfaces lead to either poor coating universality/durability or unsatisfactory performance.In this work,therefore,we prepared coatings with adjustable surface energy by using ionic liquid grafted polyvinylidene fluoride(PVDFg-IL)with the help of water vapor induced phase separation(VIPS).VIPS plays double roles in the fabrication of PVDF-g-IL coating.On one hand,it can produce hierarchically rough structures on its surface;on the other hand,this is an efficient way to induce the enrichment of IL on coating surface.Compared with traditional coatings,PVDF-g-IL coating in this work exhibits continuously tunable surface free energy based on the exchange of counterion(free anion between Cl and PFO).As a result,the bottom interface has been enhanced via higher SFE in Cl state while the customized top interface contributes to various functions including switchable super-wettability and optimized adsorption performances.The specific research contents include the following three aspects:(1)PVDF-g-IL coating: preparation via VIPS and manipulation of surface free energy: Based on excellent miscibility of PVDF and the adopted IL,IL was fixed on the PVDF molecular chain by electron beam radiation;Then,PVDF-g-IL coating has been prepared with the help of vapor induced phase separation(VIPS).There are both hierarchically rough structures and enrichment of IL on coating surface.The surface free energy has been measured.Its magnitudes can be tailored via the exchange of counterion(free anion between Cl and PFO)which has been validated by means of XPS and FTIR.(2)Roles of tunable surface free energy at dual-phase interface: The bonding performance at bottom interface and wettability at top interface of PVDF-g-IL coating have been investigated in detail.In the former,the bonding performance between PVDF and EVA(ethylene vinyl acetate copolymer)has been assessed via T-type peeling test.After PVDF-g-IL coating treatment,the bonding strength has been improved significantly(from 200 N/m to about 950 N/m);In the latter,the combination of hierarchical roughness and tunable SFE contributes to switchable super-wettability(0°～150°),producing significant influence on printing and gating.(3)Roles of tunable surface free energy at multi-phase interface: The adsorption behaviors of PVDF-g-IL coating have been investigated by taking perfluorinated compounds and microplastics as model system.A novel “serial adsorption” strategy has been developed,in which PVDF-g-IL coating can effectively capture perfluorinated compounds and microplastics at the same time with enhanced adsorption dynamics and capacity.It can be attributed to the following reasons.Firstly,hierarchically rough structure can provide more adsorption sites;Secondly,the adsorption of perfluorinated compounds enhances the hydrophobic interaction between the coating and microplastics;Finally,the influence of air cushion has been depressed during the adsorption of microplastics.