Latex-based concept for the preparation of graphene-based polymer nanocomposites

Abstract

The latex technology concept is applied for the preparation of graphene/polystyrene nanocomposites. Aqueous dispersions of graphene are obtained via oxidation and exfoliation of graphite and subsequent reduction in the presence of surfactant. The quality of the prepared nanofillers is characterized by atomic force microscopy (AFM). Different amounts of aqueous graphene dispersions are then mixed with polystyrene (PS) latex and composites are prepared by freeze-drying and subsequent compression molding. The final bulk and local conductivities of the composites are respectively measured by a fourpoint method and by means of conductive AFM (C-AFM) analysis. The morphology of the conductive nanocomposites is studied with charge contrast scanning electron microscopy imaging (SEM). The percolation threshold for conduction is below 1 wt% of graphene in the composites, and a maximum conductivity of about 15 S m À1 can be achieved for 1.6-2 wt% nanofiller.

Graphene-philic surfactants for nanocomposites in latex technology

“…With regard to nanofiller properties, Zuberi et al [81] and Lisunova et al [82] both presumed that the presence of a surfactant insulating layer atop the nanofiller surface would hinder the electron mobility between the nanofiller conductive network to give higher resistivity values. Recently, Tkalya et al [27] also showed this, by using high surfactant levels (up to 10-fold excess) to obtain stable graphene dispersions. The presence of excess surfactant in the final composites was acknowledged to affect the ability of graphene to fully enhance the electrical conductivity of the resulting nanocomposites.…”

“…This change corresponds to the formation of a filler network within the matrix for enhanced electron mobility [17,76]. The versatility of latex technology to offer low percolation threshold and relatively high conductivity immediately stimulated others to work in this area, with much success [27,38,44,61]. Also spurred on by the desire to minimize the use of organic solvents, so-called volatile organic compounds (VOCs).…”

“…The hydrocarbon polymer polystyrene (PS, compound 9 Table 2) was amongst the first materials to be investigated for graphene/polymer nanocomposites based on latex technology [27]. Studies on CNT/polymer nanocomposites have provided important pointers to make conductive nanocomposite systems using this type of polymer [69,70,[171][172][173].…”

“…The first report of a graphene/polymer nanocomposite prepared using latex technology was achieved using anionic polymer, poly(sodium-4-styrenesulfonate), denoted as PSS (see Table 1 compound 7) [27]. In this study, graphene-coated PSS was synthesized by reducing graphite oxide with hydrazine in the presence of a ten-fold excess of PSS (Mw = 70 000 g/mol).…”

“…UV-Visible spectroscopy was used to quantify the dispersion state of graphene, but without supporting data [27]. It is surprising though, that such high molecular weight material should be added in excess to provide a sufficient barrier against agglomeration.…”