Aqueous Graphene Dispersions–Optical Properties and Stimuli-Responsive Phase Transfer

Abstract

We demonstrate essentially complete exfoliation of graphene aggregates in water at concentrations up to 5% by weight (166-fold greater than previous high concentration report) using recently developed triblock copolymers and copolymeric nanolatexes based on a reactive ionic liquid acrylate surfactant. We demonstrate that the visible absorption coefficient in aqueous dispersion, 48.9 ± 1.3 cm(2)/mg at 500 nm, is about twice that currently accepted, and we show that this value is a greatest lower bound to extant macroscopic single sheet optical studies of graphene when one considers both fine structure constant and excitonic mechanisms of visible absorption. We also show that dilute and concentrated graphene dispersions are rheo-optical fluids that exhibit an isotropic to nematic transition upon application of a shear field, and we demonstrate stimuli-responsive phase transfer.

Supercritical Fluid‐Facilitated Exfoliation and Processing of 2D Materials

“…[154] These yields, at least, do not depend on visible absorption coefficient. [156] The experimental results of Nair and co-workers agree with the fine structure constant-based value, 91 cm 2 mg −1 in dispersion (2/3 the value for light polarized parallel to a graphene plane), for randomly oriented nanosheets. [155] One inconsistency that is difficult to resolve in this study is that TEM of multisheet platelets exhibit the standard and well established intersheet spacing of about 0.35 nm, while the AFM data of exfoliated sheets were interpreted assuming a sheet thickness of 0.8 nm.…”

“…It should be mentioned, however, that yields 800% higher and 33% more concentrated (50 mg mL −1 ) have been reported using sonication in water. [156] This means that these estimates [70] of yield are fivefold too high. Such a thickness is consistent with graphene oxide and reduced graphene oxide, but not with pristine graphene.…”

A Kinetic Model for Exfoliation Kinetics of Layered Materials

“…We illustrate in Figure 1r ecently reported [47] apparent optical density at 500 nm as afunction of sonication time for two graphene-in-water dispersions,w herein the graphene weight concentration was 5%.T hese dispersions were stabilized using a( nanolatex) nanogel [48] derived [49,50] from ah ydrophilic imidazolium acrylate monomer that also is an ionic liquid. Thew eight ratio of nanogel to graphene was 0.5.…”

“…The apparent optical density,O D app ,w as obtained by diluting aweighed aliquot of the dispersion with water sufficiently to obtain am easured optical density in the range of 0.1 to 1.5. [47] with permission. Ther elative contribution of non-absorbing scat- Figure 1.…”

“…All effects of stabilizer (polymer) concentration, temperature,mixing,sonication, etc., are embodied in the respective rate constants,a sp seudo first-order constants.T he chopping of larger areal sheets into smaller sheets is aw ell known aspect of graphene sonication, [47] and such processes are not considered in this model. All effects of stabilizer (polymer) concentration, temperature,mixing,sonication, etc., are embodied in the respective rate constants,a sp seudo first-order constants.T he chopping of larger areal sheets into smaller sheets is aw ell known aspect of graphene sonication, [47] and such processes are not considered in this model.…”