Fluid/Fiber Interactions and the Conductivity of Inkjet Printed Ag on Textile Substrates

X-ray tomographic reconstruction reveals that the distribution of Ag after inkjet printing and sintering a nanoparticle conducting ink on a woven polyester textile substrate is strongly controlled by the fiber surface properties and fabric architecture. Capillarity confines the transport of the ink predominantly within the warp or weft yarns of the fabric and there is little transport of ink between the yarns. Changing the fiber surface energy through the Scotchgard treatment leads to an increase in the contact angle, reducing ink transport along the fibers and an increase in conductance. A similar effect is seen when printed drop spacing is reduced, increasing the local Ag concentration. Electrical conductivity is strongly influenced by the fiber density in each yarn direction and, in this case, the different densities lead to different electrical conductance values. Through the use of image segmentation, it is possible to identify a low level of electrical interconnection between the warp and weft yarns. Conductance within a yarn is shown to depend on Ag concentration via a percolation mechanism and this is confirmed by a simple model relating the volume of the largest interconnected Ag object present to the measured conductance. These results illustrate the complexity of the interaction between conductive inks and fibrous substrates and that concepts, such as sheet resistance, used to characterize printed conductors on solid substrates are not applicable to textile substrates.