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 morphology forming abilities of two dissimilar polyion complex (PIC)-based double hydrophilic block copolymers (DHBC) along with three different phenol concentrations when subjecting the blend in aqueous media via a hydrothermal-assisted carbonization strategy. The morphological transition from worm-like to spherical along with granular is found for the blend of oppositely charged poly(ethylene glycol) (PEG)-conjugated poly(amino acid) block copolymers, PEG-poly(l-lysine) (PEG-PLys) and PEG-poly(glutamic acid) (PEG-PGlu), along with three different concentrations of phenol. In contrast, after mixing the combination of PEG-PLys and PEG-poly(aspartic acid) (PEG-PAsp) separately with three different phenol contents, elliptical to irregular to spherical structural transition occurred. Fourier transform infrared and circular dichroism spectroscopic studies indicated that the formation of worm-like hybrid micellar structures is attributed to the presence of the ß-sheet structure, whereas spherical-shaped hybrid micellar structures are formed due to the existence of α-helix and random coil structures. We discuss the mechanism for the secondary structure-induced morphology formation based on the theory related to the packing parameter, which is commonly used for analyzing the shape of the micellar structures. Secondary structures of the PIC-based DHBC system are responsible for forming multiple carbon morphologies, whereas these structures are 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 carbon morphologies. Scanning electron microscopy observations suggested there is no significant morphological change even after subjecting the hybrid micelles to carbonization at elevated temperatures. Raman scattering studies revealed that the degree of graphitization and the graphitic crystallite domain size of the carbonized sample depend on the phenol content. Carbon materials exhibited the highest specific surface area of 579 m2 g-1 along with a pore volume of 0.398 cc g-1, and this observation suggests that the prepared carbons are porous. Our findings illustrate the facile and effective strategy to fabricate the multiple carbon morphologies that can be used as potential candidates for energy storage applications.