A bio-enabled, environmentally-friendly, and maximally mild layer-by-layer approach has been developed to surface modify inherently hydrophobic Kapton HN substrates to allow for great printability of both water- and organic solvent-based inks thus facilitating the full-inkjet-printing of flexible electronic devices. Different from the traditional Kapton surface modification approaches which are structure-compromising and use harsh conditions to target, and oxidize and/or remove part of, the surface polyimide of Kapton, the present Kapton surface modification approach targeted the surface electric charges borne by its additive particles, and was not only the first to utilize environmentally-friendly clinical biomolecules to build up a thin film of protamine-heparin complex on Kapton, but also the first to be conducted under minimally destructive and maximally mild conditions. Besides, for electrically charged ink particles, the present surface modification method can enhance the uniformity of the inkjet-printed films by reducing the “coffee ring effect”. As a proof-of-concept demonstration, reduced graphene oxide-based gas sensors, which were flexible, ultra-lightweight, and miniature-sized, were fully-inkjet-printed on surface modified Kapton HN films and tested for their sensitivity to dimethyl methylphosphonate (a nerve agent simulant). Such fabricated sensors survived a Scotch-tape peel test and were found insensitive to repeated bending to a small 0.5 cm radius.

This work describes a facile, mild and general wet chemical method to change the material and the geometry of inkjet-printed interdigitated electrodes (IDEs) thus drastically enhancing the sensitivity of chemiresistive sensors. A novel layer-by-layer chemical method was developed and used to uniformly deposit semiconducting single-wall carbon nanotube (SWCNT)-based sensing elements on a Kapton^® substrate. Flexible chemiresistive sensors were then fabricated by inkjet-printing fine-featured silver IDEs on top of the sensing elements. A mild and facile two-step process was employed to convert the inkjet-printed dense silver IDEs into their highly porous gold counterparts under ambient conditions without losing the IDE-substrate adhesion. A proof-of-concept gas sensor equipped with the resulting porous gold IDEs featured a sensitivity to diethyl ethylphosphonate (DEEP, a simulant of the nerve agent sarin) of at least 5 times higher than a similar sensor equipped with the original dense silver IDEs, which suggested that the electrode material and/or the Schottky contacts between the electrodes and the SWCNTs might have played an important role in the gas sensing process.

Kapton HN films were surface modified, for the first time, by taking advantage of their additive and using only weak polyelectrolytes, for all-inkjet-printed flexible electronic devices.

Kapton polyimide films are one of the most commonly used flexible and robust substrates for flexible electronic devices due to their excellent thermal, chemical, mechanical, and electrical properties. However, such films feature an inert and highly hydrophobic surface that inhibits the deposition of functional materials with water-based fluids (solutions, suspensions, inkjet inks, etc.), which raise the need for their surface modification to reduce their inherent surface inertness and/or hydrophobicity in order to allow for the fabrication of electronic devices on the substrates. Traditional Kapton surface modification approaches use harsh conditions that not only cause environmental and safety problems but also compromise the structural integrity and the properties of the substrates. This chapter focuses on two recently-developed mild and environmentally friendly wet chemical approaches for surface modification of Kapton HN films. Unlike the traditional methods that target the polyimide matrix of Kapton films, these two methods target the slip additive embedded in the polyimide matrix. The surface modified Kapton films resulted from these two methods allowed for not only great printability of both water- and organic solvent-based inks (thus facilitating the full-inkjet-printing of entire flexible electronic devices) but also strong adhesion between the inkjet-printed traces and the substrate films.