Influence of Textile Architecture on the Electrical Resistivity of Inkjet Printed Ag Nanoparticle Inks

Textile substrates provide promising platforms for wearable technology that can provide both strength and flexibility making them potentially more comfortable to wear than rigid wearable alternatives. They can be made stretchable, breathable, and washable and are easily integrated into clothing. Inkjet printing is widely used to fabricate printed electronic devices and is also a common tool for patterning textiles. However, it is well known that the rough and porous textile surface makes it difficult to reliably print electrically conductive structures onto textile substrates. Here we report the use of X-Ray computed tomography (CT) to reveal the distribution of Ag ink after ink jet printing onto polyester textile substrates. CT images clearly show that the penetration of ink into the textiles is strongly influenced by the fibrous architecture of the fabric with capillarity confining the ink within the yarn tows running in the warp and weft directions of the weave. We have used image segmentation methods to identify connectivity of the silver objects after heat treatment and this demonstrates that connectivity, and hence electrical conductance, is less likely between tows running in each direction. This information shows that the electrical conductivity of a printed patch of Ag ink can be represented by a number of electrically independent Ag networks running in parallel and that the conductivity scales approximately with the size of the largest Ag network present.<br/><br/>Here we use CT imaging to analyse the distribution of Ag after printing and sintering in 6 different woven fabrics each made from the same polyester fibre with fibre diameter either 10 μm or 16 μm. Each fabric is a plain weave but with different yarn and fibre densities giving fabric weights in the range 80 – 450 g.cm^-2. We used a Fujifilm Dimatix 2800 to print 10 pL drops of a Ag nanoparticle ink at 10 μm drop spacing, with 5 layers of overprinting, to print identical patterns on each textile. After sintering at 150 °C the electrical properties of individual yarn tows in the fabric were measured using a 4-point probe. The printed fabric conductance values span three orders of magnitude, confirming the strong influence of fibre architecture on electrical properties. Image segmentation of the CT results from each fabric conclusively shows that the highest electrical conductance correlates with the presence of largest volume amongst the interconnected Ag objects. Three of the fibre architectures that show the highest electrical performance have equivalent conductivity values that are over an order of magnitude lower than that of bulk Ag and are also considerably lower than that achievable by inkjet printing Ag inks onto polymer film substrates. This work confirms that textile substrates can be used as substrates for printed conducting structures and that the fibre architecture controls the distribution of ink, the likely precision and resolution of deposition, as well as the conductivity of the printed structure.