Ion Transfer Properties of Layer-by-Layer Films During Contact Electrification

The work reports the interesting charging behaviors of layer-by-layer (LBL) films of strong polyelectrolytes and the role of ion transfer during contact electrification of these films. When they were brought into contact with another material (e.g., stainless steel), films with polycations as the outermost layer typically developed positive charge, while films with polyanions as the outermost layer developed negative charge. We exploited the system to create a naturally antistatic surface by fabricating LBL films terminated with a mosaic layer of polycations and polyanions using microcontact printing. The charging properties of such films were continuously tunable and full switchable. We also investigated the ion specific effects in the ion transfer process, and found that the propensity of the ion transfer properties followed a Hofmeister ion series: the most kosmotropic ions such as hydroxide and fluoride are more likely to transfer while the most chaotropic ions such as iodide and perchlorate barely transfer at all.