Nanoscale Morphology and Electrical Behaviour of a Pressure Sensitive Ink

Pressure Sensitive Ink is an electrically conductive composite material made by Peratech Ltd. The conductivity of the inks is sensitive to touch pressure, which have a range of applications in areas including telecommunications and robotics and are printable as functional electronic devices. The inks are complex and composed of electrically conductive acicular (needle-like) refractory filler particles dispersed in an insulating organic base ink. Inks mixed, prepared and stored in a variety of conditions have been studied using high resolution scanning and transmission electron microscopy, focused ion beam and EDX elemental analysis in conjunction with DC electrical characterization. The research has aimed to investigate possible links between the structure and electrical behaviour of the inks. The results have shown that inks stored for greater amounts of time, prior to printing, lose touch sensitivity. Causes for this are uncertain, but may be linked with the growth of nanoscale features on the filler particles and partial settling of constituents. EDX analysis revealed candidate elements for the nanoscale features found on filler particles. Modeling current-voltage plots with non-linear fits has shown there might be a switching of conduction mechanism with increasing compression of the inks. Additionally, the unclear process by which inks lose touch sensitivity was shown to be temperature dependent. Inks more vigorously blended were found to have shorter filler particles through a statistical survey of filler particle lengths, measured through scanning electron microscopy imaging. Inks produced with a lower filler particle to base ink ratio were found to be less sensitive to touch pressure than those made with comparatively more filler particles. A survey of filler particle clumps (groups of 3 or more particles) revealed that the addition of hyper-dispersant, an anti – clumping chemical agent, aided better dispersion of filler particles and increased the touch sensitivity of low filler particle fraction inks.