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Keywords:
2D materials; atomic force microscopy; liquid phase exfoliation; nanomaterials; talc
Abstract
Industrial applications of nanomaterials require large-scale production methods, such as liquid phase exfoliation (LPE). Regarding this, it is imperative to characterize the obtained materials to tailor parameters such as exfoliation medium, duration, and mechanical energy source to the desired applications. This work presents results of statistical analyses of talc flakes obtained by LPE in four different media. Talc is a phyllosilicate that can be exfoliated into nanoflakes with great mechanical properties. Sodium cholate at two different concentrations (below and at the critical micelar concentration), butanone. and Triton-X100 were employed as exfoliation medium for talc. Using recent published statistical analysis methods based on atomic force microscopy images of thousands of flakes, the shape and size distribution of nanotalc obtained using the four different media are compared. This comparison highlights the strengths and weaknesses of the media tested and hopefully will facilitate the choice of the medium for applications that have specific requirements.
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Introduction
Two-dimensional (2D) materials have attracted a lot of interest due to their outstanding properties [1]. However, large-scale production is still a challenge that needs to be addressed to integrate 2D materials into industrial applications. One approach to producing large quantities of few-layer flakes of a broad range of exfoliatable materials is liquid-phase exfoliation (LPE) [2-5].
This method relies on mechanical energy to exfoliate materials in an appropriate liquid medium. To exfoliate a material of interest, it must be reduced to a fine powder and mixed with a liquid that serves as an exfoliation medium. The solution is exposed to a mechanical energy source that leads to the delamination of the material, resulting in a suspension of nanosheets [6]. The energy may be provided by an ultrasonic bath, a shear force mixer, or a tip sonicator. The solution serves three purposes: it provides a medium to propagate the mechanical energy, suspends the exfoliated nanosheets, and prevents them from agglomerating again. The versatility of the method allows it to be employed to obtain nanoflakes of a collection of materials such as graphene [3.7], hexagonal boron nitride [8], transition metal dichalcogenides [9], and others [10.11].
Although the experimental setup is generally designed as described before [6], numerous parameters...