Abstract
In this study, liquid droplets of 1-allyl-3-methylimidazolium dicyanamide have been processed by initiated chemical vapor deposition (iCVD) with a cross-linked polymer film consisting of (hydroxyethyl)methacrylate and ethylene glycol dimethacrylate to develop free-standing, ion-conductive membranes. We found that the obtained films are solids and have a conductivity of up to 18 ± 6 mS/cm, associated with the negatively charged counterion, indicating no loss of conductivity, compared to the ionic liquid in the liquid state. The membranes were conductive within a large process window and in air, thanks to the fact that the iCVD process does not affect the mobility of the anion in the ionic liquid. Furthermore, we demonstrate that varying the deposition conditions can influence the homogeneity and conductivity of the resulting membranes. The promising results of this study represent an important stepping stone on the way to novel ion-conductive membranes.
Highlights
Ionic liquids (ILs) are salts that are liquid below 100 °C, many are still in their liquid state at room temperature
It has been shown that HEMA is able to penetrate ionic liquid droplets and enhances their spreading during initiated chemical vapor deposition (iCVD).[39]
Profilometry and dynamic contact angle (dCA) measurements proved that precoating the substrates before drop-casting the liquid IL results in better spreading of AMID and leads to more uniform solid films
Summary
Ionic liquids (ILs) are salts that are liquid below 100 °C, many are still in their liquid state at room temperature. ILs can be tailored to specific applications by changing sidechains or functional groups, contributing to their versatility.[1,2] their high proton or anion conductivity makes ionic liquids highly attractive for a large variety of new applications, including but not limited to their use as solvents,[3,4] electrolytes[5−7] especially for Li-ion batteries,[8−10] for separation processes,[11,12] heat storage,[13] or utilizing them as proton-exchange membranes in fuel cells.[14−16] For many applications, it would be much easier to handle ILs in a solid state in the form of a membrane. We propose the development of a solidification process for ILs that ensures retention of sufficiently high conductivity to apply the resulting ion-conductive membranes in the desired electrochemical applications. The other ion remains unbound and mobile in the solid membrane, leading to conservation of a significant amount of initial conductivity
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