Chiroptical, morphological and conducting properties of chiral nematic mesoporous cellulose/polypyrrole composite films

Abstract

In this work, we describe novel conducting chiral nematic composites prepared via in situ oxidative chemical polymerization of pyrrole onto modified chiral nematic cellulose nanocrystal (CNC) films. The surface of free-standing iridescent CNC films was modified by four different approaches including TEMPO-oxidation, acetylation, desulfation and cationization after the fabrication of sulfated CNC films by evaporation-induced self-assembly (EISA). Structural, thermal, optical and morphological features of the modified films were further evaluated. The modified CNC films show enhanced thermal stability of more than 95 °C relative to the acid form of the CNCs. The chiroptical properties could be customized to yield vibrant iridescent colors ranging from cyan-green to red by the surface treatments. Moreover, our experimental findings reveal that the surface modification approach allows the swelling behavior of the iridescent CNC films to be tailored, a property with potential for the fabrication of novel security devices. Conductive CNC/PPy composite films were prepared by in situ oxidative polymerization of pyrrole onto CNC surfaces using FeCl₃ and HCl as oxidizing agent and dopant, respectively. PPy was also polymerized onto chiral nematic mesoporous cellulose (CNMC) structures obtained through a concomitant assembly of CNCs and condensation of tetramethoxysilane (TMOS) to fabricate porous structures with enhanced specific charge capacity. Results reveal that the chiral nematic structure of CNCs could be replicated by the PPy coating. Furthermore, it was found that the electrochemical performance of CNC/PPy composites was improved after the development of mesoporous structures. These new, easily prepared materials are attractive candidates for environmentally friendly sensors and energy storage devices.