Conductive Polymer-Coated Threads as Electrical Interconnects in e-Textiles

An organic polymer electrical interconnect is demonstrated. The ionomer mixture poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS; 1:2.5, w:w) was cast onto silk fibers from a 50:50 (v:v) ethylene glycol solution by a dip-coating process. Dynamic mechanical analysis (DMA) results show that Young's modulus and mechanical strength are maintained during the coating process from acidic solution (pH similar to 1). DMA dynamic temperature scans reveal two new thermal transitions once PEDOT:PSS is applied to the silk fiber, and they are assigned to the glass transition temperature (59 degrees C) and melting point (146 degrees C) of the ionomer pair. Electrical conductivities of 8.5 S/cm were achieved with four cycles of the dip-coating process, only 10x less than Ag-coated thread control samples. SEM imaging of the PEDOT:PSS-coated fibers show slight texturing to the fibers due to the coating, as well as significant charging in the uncoated samples when compared to PEDOT:PSS-coated samples. The conductive fibers fabricated by this process were successfully applied as electrical interconnects in flexible, fully functional 555 timer circuits stitched into fabric substrates.