Influence of relative humidity on the structure, swelling and electrical conductivity of PEDOT:PSS fibers

Abstract

PEDOT:PSS is a conducting polymer with a wide variety of applications in the field of organic electronics. Over the past few years our group has developed PEDOT:PSS fibers with high electrical conductivity and robust mechanical properties, and we have observed changes in their properties that seemed to stem from seasonal changes in atmospheric relative humidity. In this work, we report the influence of relative humidity on the swelling, electrical conductivity and structure of wet-spun PEDOT:PSS fibers. The diameter of the fibers linearly increased with relative humidity up to the 70–80% range where the increase became exponential. The electrical conductivity reversibly decreased with increasing relative humidity with a similar linear and then exponential behavior. Additionally, an irreversible decrease (aging) in electrical conductivity was also observed. To gain more insight into the structural origin of these changes, wide angle x-ray scattering of the PEDOT:PSS fibers were gathered at different relative humidities in the 10–90% range so that the changes in structure could be observed in situ. On one hand, the lamella stacking distance of PEDOT and PSS chains increased linearly up to the 70–80% relative humidity range where the increase became exponential. On the other hand, the π-π stacking distance between PEDOT chains remained unaltered. We found that the changes in the lamella stacking distance were closely correlated to the changes observed for the diameter and electrical conductivity.