High-Concentration, Surfactant-Stabilized Graphene Dispersions

TLDR

The study presents a method to produce graphene dispersions stabilized in water with sodium cholate at concentrations up to 0.3 mg/mL. The process employs low‑power sonication for up to 400 h followed by centrifugation to generate stable dispersions. The method yields dispersions whose concentration rises with sonication time and whose quality is optimal at centrifugation rates of 500–2000 rpm; TEM shows 1–10‑layer flakes averaging ~4 layers and ~1 µm in length, largely defect‑free below 2000 rpm, and the dispersions can be cast into high‑quality free‑standing films, demonstrating scalable liquid‑phase processing for diverse applications.

Abstract

A method is presented to produce graphene dispersions, stabilized in water by the surfactant sodium cholate, at concentrations up to 0.3 mg/mL. The process uses low power sonication for long times (up to 400 h) followed by centrifugation to yield stable dispersions. The dispersed concentration increases with sonication time while the best quality dispersions are obtained for centrifugation rates between 500 and 2000 rpm. Detailed TEM analysis shows the flakes to consist of 1−10 stacked monolayers with up to 20% of flakes containing just one layer. The average flake consists of ∼4 stacked monolayers and has length and width of ∼1 μm and ∼400 nm, respectively. These dimensions are surprisingly stable under prolonged sonication. However, the mean flake length falls from ∼1 μm to ∼500 nm as the centrifugation rate is increased from 500 to 5000 rpm. Raman spectroscopy shows the flake bodies to be relatively defect-free for centrifugation rates below 2000 rpm. The dispersions can be easily cast into high-quality, free-standing films. The method extends the scope for scalable liquid-phase processing of graphene for a wide range of applications.