A novel, facile, layer-by-layer substrate surface modification for the fabrication of all-inkjet-printed flexible electronic devices on Kapton

A facile, environmentally-friendly, low-cost, and scalable deposition process has been developed and automated to apply polyelectrolyte multilayers (PEMs) on flexible Kapton HN substrates. Two weak polyelectrolytes, poly(acrylic acid) and polyethylenimine, were deposited in an alternating, layer-by-layer fashion under controlled pH and ionic strength. Compared to strong polyelectrolytes, weak electrolytes can control the properties of the PEMs more systmatically and simply. To our knowledge, this work on surface modification of Kapton is not only the first to use only weak polyelectrolytes, but is also the first to take advantage of the surface properties of calcium-bearing additive particles present in Kapton HN. The resulting surface-modified Kapton HN substrate allowed for the inkjet printing of water-based graphene oxide (GO) inks and organic solvent-based inks with good adhesion and with desired printability. While the deposition of a single PEM layer on a Kapton substrate significantly reduced the water contact angle and allowed for the inkjet-printing of GO inks, the deposition of additional PEM layers was required to maintain the adhesion during post-printing chemical treatments. As a conceptual demonstration of the general applicability of this PEM surface modification approach, a flexible, robust, single-layered gas sensor prototype was fully inkjet printed with both water- and ethanol-based inks and tested for its sensitivity to diethyl ethylphosphonate (DEEP), a simulant for G-series nerve agents. The electrical conductivity and morphology of the sensor were found to be insensitive to repeated bending around a 1 cm radius.