Effect of Hydrophobic Moieties in Water-Soluble Polymers on Physical Exfoliation of Graphene

Abstract

Graphene is a fascinating material with unique properties, such as high mechanical strength and excellent electronic and thermal conductivities, as well as many other beneficial properties. Despite much recent effort, the facile synthesis and colloidal stabilization of graphene in aqueous solutions remains central to both academic research and practical applications. Here, we provide an in-depth insight into how the hydrophobic moieties of polymers affect the physical exfoliation of graphite into graphenes in aqueous solution. Four different polymers with graphene-like moieties, such as phenyl- and pyrenyl-functionalized side chains, were synthesized on the basis of the two water-soluble polymers poly­(vinyl alcohol) (PVA) and dextran. Simply, sonication of graphite with the polymers in an aqueous solution produced stable graphene dispersions even after centrifugation. The ability of the polymers to exfoliate graphene sheets from the graphite was systematically investigated. Notably, 10 wt % phenyl-PVA led to the production of 46.7% bilayer and 26.7% 3- or 4-layer graphene flakes. An in-depth study into this and similar results was performed using density functional theory and MMFF94 computational tools, which led to better understanding of the interaction between graphene and the polymers in the solution. The polymers used can efficiently cleave graphite into graphene pieces without significant degradation of the sp2 carbon bonding network and then stabilize them in the aqueous solution, in contrast with the so-called “reduced graphene oxide”. This approach is advantageous for the large-scale production of high-quality, few-layer graphene. Moreover, a judicious combination of the parent polymer backbone and the functional side chains might allow the control of the size and number of layers of the graphene flakes made in the aqueous solution. Lastly, graphene gels were directly prepared from the aqueous graphene/polymer solution; further, their potentials for two model applications, as a dye adsorbent and gel electrolyte, were demonstrated.

Supramolecular Approaches to Graphene: From Self‐Assembly to Molecule‐Assisted Liquid‐Phase Exfoliation

“…Over the past years, it has been proven that graphene can be dispersed in water by using a wide range of polymers acting as DSAs, [14,195,197,198,[215][216][217][223][224][225][226][227][228][229][230][231][232] such as cellulose acetate (CA), [233] ethyl cellulose (EC), [229] polyvinylpyrrolidone (PVP), [224] lignin, [230] gum arabic (GA), [225,226] gelatin derived from animal skin and bones, [227] and even more complex systems such as bovine serum albumin (BSA), [223] hyaluronan (PyHA) [216] and DNA [198] functionalized with pyrene head-groups.…”

“…In this framework, Yoon and co-workers have shown that graphene dispersions can be stabilized by four different polymers based on either poly(vinyl alcohol) (PVA) or dextran functionalized with conjugated moieties, such as phenyl or pyrene (see PyDT and PyPVA in Figure 10). [217] The ability of these polymers to stabilize graphene dispersions was systematically investigated. Moreover, graphene hydrogels and aerogels were prepared from the aqueous dispersion of the graphene/polymer.…”

Chemical functionalization and characterization of graphene-based materials

“…In any case, the strong polymer/graphene interactions make extremely difficult to separate the produced composites, which in some cases resulted in interesting materials. In this connection, Yoon and co-workers produced stable graphene dispersions by simply sonicating graphite with four different polymers based on either poly(vinyl alcohol) (PVA) or dextran 123. The water-soluble polymers with phenyl-and pyrenyl-functionalized side chains facilitated the formation of stable aqueous dispersions of graphene without degrading its sp 2 hybridized structure.…”

Exfoliation of 2D Materials for Energy and Environmental Applications

“…The chemical structures of such polymers can be modified for the aqueous dispersion of 2D nanomaterials. A recent work reported the synthesis of four different polymer derivatives by using two well‐known water‐soluble polymers, PVA and DT, for the physical exfoliation of graphite in aqueous solutions . PVA and DT were chosen owing to their ability to disperse single‐walled carbon nanotubes in aqueous solutions.…”