Multiple Carbon Morphologies Derived from Polyion Complex-Based Double Hydrophilic Block Copolymers as Templates and Phenol as a Carbon Precursor

Abstract

This study demonstrates the multiple carbon morphologyformingabilities of two dissimilar polyion complex (PIC)-based double hydrophilicblock copolymers (DHBC) along with three different phenol concentrationswhen subjecting the blend in aqueous media via a hydrothermal-assistedcarbonization strategy. The morphological transition from worm-liketo spherical along with granular is found for the blend of oppositelycharged poly(ethylene glycol) (PEG)-conjugated poly(amino acid) blockcopolymers, PEG-poly(l-lysine) (PEG-PLys) and PEG-poly(glutamicacid) (PEG-PGlu), along with three different concentrationsof phenol. In contrast, after mixing the combination of PEG-PLysand PEG-poly(aspartic acid) (PEG-PAsp) separately with threedifferent phenol contents, elliptical to irregular to spherical structuraltransition occurred. Fourier transform infrared and circular dichroismspectroscopic studies indicated that the formation of worm-like hybridmicellar structures is attributed to the presence of the & beta;-sheetstructure, whereas spherical-shaped hybrid micellar structures areformed due to the existence of & alpha;-helix and random coil structures.We discuss the mechanism for the secondary structure-induced morphologyformation based on the theory related to the packing parameter, whichis commonly used for analyzing the shape of the micellar structures.Secondary structures of the PIC-based DHBC system are responsiblefor forming multiple carbon morphologies, whereas these structuresare absent in the case of the amphiphilic block copolymer (ABC) system.Furthermore, ABC-based template methods require organic solvent, ultrasonication,and a prolonged solvent evaporation process to obtain multiple carbonmorphologies. Scanning electron microscopy observations suggestedthere is no significant morphological change even after subjectingthe hybrid micelles to carbonization at elevated temperatures. Ramanscattering studies revealed that the degree of graphitization andthe graphitic crystallite domain size of the carbonized sample dependon the phenol content. Carbon materials exhibited the highest specificsurface area of 579 m(2) g(-1) along witha pore volume of 0.398 cc g(-1), and this observationsuggests that the prepared carbons are porous. Our findings illustratethe facile and effective strategy to fabricate the multiple carbonmorphologies that can be used as potential candidates for energy storageapplications.