Shrinking rate of conducting grains in HCl–protonated polyaniline, polypyrrole, and polypyrrole/polyaniline blends with their thermal aging

Abstract

ABSTRACT:The dc electrical conductivity () of HClprotonated polyaniline, polypyrrole, and their blends was measured from 80 to 300 K for thermal aging times between approximately 0 and 600 h. The thermal aging took place at 70°C under room atmosphere. The change of with the temperature (T) and the decrease of with the thermal aging time (t) are consistent with a granular metal type structure, in which conductive grains are randomly distributed into an insulating matrix. Aging makes the grains shrink in a corrosion-like process. From ϭ (T) measurements the ratio s/d, where s is the average separation between the grains and d their diameter, as well as the rate d(s/d)/dt of their decrease with t were calculated. These revealed that the conductive grains consist of a shell, in which aging proceeds at a decreasing rate, and a central core, which is consumed at a much slower rate. Our measurements not only permitted the estimation of the shell thickness, which lies between 0 and 5 Å, but also gave quantitative information about the quality of the shells and the cores from their aging rates.

Synthesis, characterization, and thermal aging behavior of HCl‐doped polyaniline/TRGO nanocomposites

“…According to the XRD patterns, the crystallite size in the (200) plane, i.e., 25.3° does not change considerably after 500 h of thermal aging. In comparison, the results obtained for thermal aging of PANI showed that thermal aging decreases the size of conductive grains . Thus, it may be concluded that TRGO can hinder the grain size reduction by thermal aging.…”

“…D band around 1307 cm −1 and G band around 1593 cm −1 are dominant vibrational modes that are present in the Raman spectrum for graphitic structures. The intensity ratio of D to G ( I D / I G ) corresponds to disorder/order of graphene structures …”

“…In which, t is the elapsed time of thermal aging; σ and σ 0 denote the conductivity before aging and after ageing for t hours, respectively; and τ is the characteristic time of the aging process in hours. This model could be used for all ICP's except polypyrrole . An increase in τ is an indication of more stability in thermal aging.…”

“…Unfortunately, electrical conductivity of ICP's, including PANI, decreases over time which is known as aging process. Furthermore, exposing to elevated temperatures could hasten this adverse effect . In fact, in many applications, such as concentrated photovoltaic (CPV's), the temperature of the device reaches to a temperature far beyond the ambient, which could cause the conductivity of ICP's to decrease gradually.…”

“…As a result, many research efforts have been dedicated to understand the mechanism of the thermal aging process in PANI and other ICP's . Vaporization and removal of dopants, structural changes such as oxidation, crosslinking, chain scission, change in morphology, and crystalline grain size reduction have been proposed as contributing mechanisms for conductivity degradation in pure PANI . Amongst, the deprotonation of polymer backbone is known to be one of the most dominant mechanisms .…”