Challenges in Liquid‐Phase Exfoliation, Processing, and Assembly of Pristine Graphene

Abstract

Recent developments in the exfoliation, dispersion, and processing of pristine graphene (i.e., non-oxidized graphene) are described. General metrics are outlined that can be used to assess the quality and processability of various "graphene" products, as well as metrics that determine the potential for industrial scale-up. The pristine graphene production process is categorized from a chemical engineering point of view with three key steps: i) pretreatment, ii) exfoliation, and iii) separation. How pristine graphene colloidal stability is distinct from the exfoliation step and is dependent upon graphene interactions with solvents and dispersants are extensively reviewed. Finally, the challenges and opportunities of using pristine graphene as nanofillers in polymer composites, as well as as building blocks for macrostructure assemblies are summarized in the context of large-scale production.

Single‐Particle Tracking for Understanding Polydisperse Nanoparticle Dispersions

“…Whether colloidal nanoparticles are chemically synthesized or dispersed from aggregates, controlling material dimensions still presents a challenge. For carbon nanotubes and 2D materials, colloidal dispersion from aggregates is usually performed for via ultrasonication, which is a cavitation process with sufficient energy to open inside hydrophobic areas for conjugation . However, this process results in product polydispersity as a function of energy input, treatment duration, and even the particular geometry of the dispersion setup .…”

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Manganese‐Oxide‐Based Electrode Materials for Energy Storage Applications: How Close Are We to the Theoretical Capacitance?

“…However, unlike CNTs and carbon fibers, graphene and rGO are 2D planar materials and cannot be easily “woven” into 3D networks . When layers of graphene nanosheets are placed together, the restacking problem often occurs, which can severely affect the electrolyte transfer throughout the material (when restacking happens, MnO x as the active materials would be immobilized inside, and no longer be accessible by electrolyte) …”

From Flatland to Spaceland: Higher Dimensional Patterning with Two‐Dimensional Materials

“…In many cases, 2D materials are produced as dispersed nanosheets of sub‐micrometer to micrometer‐scale lateral dimension in aqueous solutions or organic solvents, particularly when prepared using solution‐based growth or exfoliation techniques . When suspended in a fluid phase, nanosheets exhibit complex behaviors that include self‐avoidance and uniform dispersion due to electrostatic repulsion, aggregation (to disordered flocs) or (re)stacking to aligned 2D multilayer flocs, liquid crystal alignment driven by large excluded volume effects associated with very high aspect ratio and high concentration, interfacial accumulation, and mechanical deformation by weak electrostatic or van der Waals forces in the liquid phase or at the liquid‐air interface or deposition substrates .…”