Abstract
A polypyrrole-carboxylic acid derivative (PPy-COOH) was covalently anchored on the surface of hexamethylene diisocyanate (HDI)-modified graphene oxide (GO) following two different esterification approaches: activation of the carboxylic acids of the polymer by carbodiimide, and conversion of the carboxylic groups to acyl chloride. Microscopic observations revealed a decrease in HDI-GO layer thickness for the sample prepared via the first strategy, and the heterogeneous nature of the grafted samples. Infrared and Raman spectroscopies corroborated the grafting success, demonstrating the emergence of a peak associated with the ester group. The yield of the grafting reactions (31% and 42%) was roughly calculated from thermogravimetric analysis, and it was higher for the sample synthesized via formation of the acyl chloride-functionalized PPy. The grafted samples showed higher thermal stability (~30 and 40 °C in the second decomposition stage) and sheet resistance than PPy-COOH. They also exhibited superior stiffness and strength both at 25 and 100 °C, and the reinforcing efficiency was approximately maintained at high temperatures. Improved mechanical performance was attained for the sample with higher grafting yield. The developed method is a valuable approach to covalently attach conductive polymers onto graphenic nanomaterials for application in flexible electronics, fuel cells, solar cells, and supercapacitors.
Highlights
Polypyrrole (PPy) and its derivatives are conductive polymers that have been extensively investigated over recent years due to their potential applications in a variety of fields including organic solar cells (OSCs), organic field-effect transistors (OFETs), organic light-emitting diodes (OLEDs), rechargeable batteries, supercapacitors, antistatic coatings, textile coatings, transducers in chemical sensors and biosensors, actuator components and fuel cells, among others [1,2,3]
It is important to mention that the hexamethylene diisocyanate (HDI)-graphene oxide (GO) samples show a lower degree of folding than typically observed for pristine GO [27], since the alkyl chains can wrap around the GO nanosheets and shield the wrinkles
The covalent anchoring of PPy-COOH onto the surface of HDI-modified GO was performed by two different esterification reactions, and the grafting yields were estimated from thermogravimetric analysis (TGA)
Summary
Polypyrrole (PPy) and its derivatives are conductive polymers that have been extensively investigated over recent years due to their potential applications in a variety of fields including organic solar cells (OSCs), organic field-effect transistors (OFETs), organic light-emitting diodes (OLEDs), rechargeable batteries, supercapacitors, antistatic coatings, textile coatings, transducers in chemical sensors and biosensors, actuator components and fuel cells, among others [1,2,3]. The improvements attained are generally insufficient to fulfill the requirements of the commercial applications Owing to their large surface area, G nanosheets have a strong tendency to form irreversible agglomerates or even restack due to van der Waals interactions, which limits property improvements [11], and such issues must be resolved to obtain a satisfactory performance of the final G-based nanocomposites. In this regard, novel strategies are pursued to improve the G dispersion and its interfacial adhesion with the PPy matrix
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