Influence of Anionic Surfactants on the Fundamental Properties of Polymer/Reduced Graphene Oxide Nanocomposite Films

Abstract

Surfactants are frequently employed in the fabrication of polymer/graphene-based nanocomposites via emulsion techniques. However, the impact of surfactants on the electrical and mechanical properties of such nanocomposite films remains to be explored. We have systematically studied the impact of two anionic surfactants [sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS)] on intrinsic properties of the nanocomposite films comprising reduced graphene oxide in a matrix of poly­(styrene-stat-n-butyl acrylate). Using these ambient temperature film-forming systems, we fabricated films with different concentrations of the surfactants (1–7 wt %, relative to the organic phase). Significant differences in film properties were observed both as a function of amount and type of surfactant. Thermally reduced films exhibited concentration-dependent increases in surface roughness, electrical conductivity, and mechanical properties with increasing SDS content. When compared with SDBS, SDS films exhibited an order of magnitude higher electrical conductivity values at every concentration (highest value of ∼4.4 S m–1 for 7 wt % SDS) and superior mechanical properties at higher surfactant concentrations. The present results illustrate how the simple inclusion of a benzene ring in the SDS structure (as in SDBS) can cause a significant change in the electrical and mechanical properties of the nanocomposite. Overall, the present results demonstrate how nanocomposite properties can be judiciously manipulated by altering the concentration and/or type of surfactant.

In Situ Surfactant Effects on Polymer/Reduced Graphene Oxide Nanocomposite Films: Implications for Coating and Biomedical Applications

“…The use of SDS as surfactant, on the contrary, resulted in high conversion of 96% at just 1 wt %, with full conversion (100%) at 3 wt % surfactant, in agreement with our previous report. 23 To ascertain the optimal long-chain alkyl acid to base molar ratio of the in situ surfactants, we first increased the amount of base (KOH) from a 1:1.2 molar ratio (SA:KOH) to 1:2 while keeping other conditions unchanged (1 wt % KSA relative to organic phase). Some of the KOH can be consumed by GO (due to deprotonation of the acid groups), and therefore increasing the amount of base will ensure complete deprotonation of acid groups in all stearic acid molecules.…”

“…The films were thermally annealed at 160 °C for 24 h to reduce GO to electrically conducting reduced GO (rGO). 16,23,31,32 All the films exhibited characteristic D and G peaks at approximately 1350 and 1585 cm −1 , respectively (Table S6). The D and G peaks are attributed to degree of structural defects in the carbon lattice and sp 2 -hybridized carbon cluster in the lattice, respectively.…”

“…All the films yielded similar values of I D / I G of ∼0.8 (Figure S3 and Table S6), confirming the reduction of GO to rGO, in agreement with previously published reports on polymer/rGO nanocomposites. 16,23,32 Confocal laser microscopy imaging of the thermally reduced films (Figure 3) reveals considerable differences between conventional (SDS) and in situ (KSA and KOA) surfactants. The rough features on the films were attributed to rGO sheets.…”

“…We have recently shown that surfactants can have a considerable impact on the properties (electrical and mechanical) of polymer/graphene oxide (GO) nanocomposite films. 23 It was observed that the commercial anionic surfactant sodium dodecyl sulfate (SDS) enhances the electrical conductivity of the nanocomposite films, fabricated by using an ambient temperature film forming system, in a concentration-dependent manner. 23 The SDS concentration dependence was postulated to be caused by the improved dispersion of GO sheets within the polymer latex, which can in part be explained by the enhanced polymerization rate (due to secondary nucleation) in miniemulsion polymerization (in situ polymerization of monomer using GO as a surfactant in a single pot).…”

“…It was concluded that surfactant effects cannot be disregarded when assessing the intrinsic properties of nanocomposite films, and indeed, film properties can be manipulated by judicious selection of type and concentration of surfactant. 23 The mechanism of miniemulsion polymerization involves transformation of surfactant stabilized submicrometer size monomer droplets (which function as individual nanoreactors) dispersed in a continuous liquid phase (usually water) to the corresponding polymer particles via droplet nucleation. Because of its amphiphilic properties, GO can function as surfactant in aqueous miniemulsion polymerization, providing a synthetic route to polymeric nanoparticles coated with GO.…”