Abstract
Despite the superior properties of graphene, the strong π–π interactions among pristine graphenes yielding massive aggregation impede industrial applications. For non-covalent functionalization of highly-ordered pyrolytic graphite (HOPG), poly(2,2,2-trifluoroethyl methacrylate)-block-poly(4-vinyl pyridine) (PTFEMA-b-PVP) block copolymers were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization and used as polymeric dispersants in liquid phase exfoliation assisted by ultrasonication. The HOPG graphene concentrations were found to be 0.260–0.385 mg/mL in methanolic graphene dispersions stabilized with 10 wt % (relative to HOPG) PTFEMA-b-PVP block copolymers after one week. Raman and atomic force microscopy (AFM) analyses revealed that HOPG could not be completely exfoliated during the sonication. However, on-line turbidity results confirmed that the dispersion stability of HOPG in the presence of the block copolymer lasted for one week and that longer PTFEMA and PVP blocks led to better graphene dispersibility. Force–distance (F–d) analyses of AFM showed that PVP block is a good graphene-philic block while PTFEMA is methanol-philic.
Highlights
Graphene, a two-dimensional structured material, is a type of carbon allotrope exhibiting a hexagonal structure with sp2 -bonding
Adhesion forces between the block (PTFEMA block or PVP block) and graphene surface were investigated by measuring Force–distance (F–d) curves obtained with an atomic force microscope (AFM, XE-7, Park System, Suwon, Korea) with modified cantilevers
In the case of pristine highly-ordered pyrolytic graphite (HOPG) dispersion, there was no graphene in the supernatant solution due to the rapid sedimentation, the bottom precipitates were taken for analyses
Summary
A two-dimensional structured material, is a type of carbon allotrope exhibiting a hexagonal structure with sp2 -bonding This unique structure gives superior properties, such as light transparency [1], mechanical strength [2], thermal conductivity [3,4], and electron mobility [5], amongst others. Liquid-phase exfoliation has been considered as the most efficient approach for industrial applications due to its low cost for mass production [20] Both covalent and non-covalent functionalizations of graphene have been extensively studied in liquid-phase exfoliation. In order to prepare stable graphene dispersions with minimal aggregation, various types of solvents (e.g., inorganic, organic, and fluorinated oils) and surfactants (ionic, non-ionic, short, and polymeric) have been exploited [26,27,28,29]. Graphene dispersions were prepared from highly-ordered pyrolytic graphite (HOPG) in methanol with four different types of PTFEMA-b-PVP block copolymers, and the characteristics of their dispersion states were investigated
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