Characteristics of the electroosmotic flow of non-aqueous electrolyte systems

The original goal was to study polysulfides in a sulfur battery by capillary electrophoresis (CE). Polysulfides are unstable and difficult to determine. Even different solvents have different effects on polysulfide equilibrium reactions. Consequently, the same solvent and electrolyte salt as in sulfur batteries had to be used in CE: 1,2-Dimethoxyethane (DME); Bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) However, this non-aqueous electrolyte system has some interesting properties in terms of electroosmotic flow: The use of DME electrolyte shows cathodic electroosmotic flow, see start point (A) in the following diagram; Mix of electrolyte with Methanol (at a ratio > 50 %): the following diagram shows the electroosmotic flow, which changes from cathodic (A) to anodic (B); Counterion (Li, Na and K) of Bis(trifluoromethane)sulfonimide show different electroosmotic mobilities. Unfortunately, the CE cannot be used for the analysis of polysulfides, since migrating polysulfides in the electric field show unavoidable degradation processes due to rapid equilibrium reactions, e.g. S62- into S3BL -. Nevertheless, the investigation of the electroosmotic flow was quite interesting and will be discussed here. Pictorial and schematic representations of the capillary inner surface are suggested to explain the direction and rate of the electroosmotic mobility.