Preparation and characterization of graphite nanosheets from ultrasonic powdering technique
Introduction
Nanocomposites of polymers with inorganic materials have been shown to exhibit a significant increase in the properties of polymers and even generate certain new properties that cannot be derived from their counterparts, as the mixing of phases in them occurs over a much smaller length scale in comparison to the micrometer length scale of conventional composites [1], [2], [3], [4]. Since the pioneer work of Toyota researchers [5], [6], and especially the report of Giannelis et al. [7], the field of polymer/silicate has gained large momentum recently [8], [9], [10]. If layered silicates are well dispersed within the polymers, either intercalated or delaminated nanocomposites are formed, leading to great enhancement of mechanical, thermal and barrier performance in comparison to conventional composites [11]. Unfortunately, silicate reinforced nanocomposites do not exhibit electrical properties as good as those of some conducting composites such as graphite-containing composites.
Similar to layered silicates, natural flake graphite is another layered material. The graphite crystal lattice consists of graphene layers formed by sp2 hybridized carbon atoms, while the carbon sheets are bounded by weak van der Waals forces with each other. Graphite is a good electrical conductor with an electrical conductivity in the range of 104 S/m at room temperature [12]. Therefore, graphite can be a good candidate in fabricating polymer conducting nanocomposites. However, unlike several lamellar silicate solids [13] whose exfoliation can be achieved by ion exchange reactions, exfoliation of graphite cannot be achieved in the same way because it does not bear any net charge. We achieved the nanodispersion composites via an in situ polymerization of monomer in the presence of graphite nanosheets which were made by powdering the exfoliated graphite with ultrasonic irradiation [14], [15]. In this paper, characterization of the graphite nanosheets will be presented; the effect of the ultrasonic irradiation on the exfoliation of graphite will be investigated.
Section snippets
Materials
Natural flake graphite with an average diameter of 500 μm was used for preparing the exfoliated graphite. Concentrated sulfuric acid and fuming nitric acid (chemically pure) were used as chemical intercalate and oxidizer to prepare graphite intercalation compounds GICs. 95% (v/v) alcohol (chemical pure) and distilled water were used as solvents for preparation of foliated graphite nanosheets.
Preparation of exfoliated graphite and foliated graphite
Exfoliated graphite (EG) was prepared according to the methods reported in the literatures [16], [17].
Powdering of exfoliated graphite
Ultrasonic irradiation has long been a very useful tool in the fields of chemistry and material engineering [18]. It is well known that when ultrasonic wave passes through a liquid acoustic cavitation takes place, and produces localized hot spots with temperature as high as 5000 °C and local pressure as high as 500 atm, with heating and cooling rates greater than 109 K/s. Acoustic cavitation near a solid surface can create localized erosion, induce high-velocity interparticle collisions, cause
Conclusions
In this study, natural flake graphite was expanded into exfoliated graphite via an acids intercalation procedure. The resulting exfoliated graphite is a worm-like particle composed of graphite sheets with thickness in the nanometer scale. Subjecting to ultrasonic irradiation, the exfoliated graphite is effectively further foliated into isolated graphite nanosheets. SEM, TEM, SAD, laser counting, and BET measurements revealed that the as-fabricated graphite nanosheets were about 52 nm in
Acknowledgements
This work was sponsored by the National Natural Science Foundation of China, No. 20174012.
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