Metal-based cationic and anionic surfactant ionic liquids determine the dispersion stability of reduced graphene...

The properties and graphene compatibility of anionic and cationic surfactant ionic liquids containing a C12 hydrophobic chain are described. The cationic surfactant ionic liquids are similar to the commercial dodecyltrimethylammonium bromide (DTAB) and dodecylethyldimethylammonium bromide (DDAB), but with a modified hydrophilic moiety bearing an iron(III) chloride, denoted as DTAF (dodecyltrimethylammonium trichloromonobromoferrate) and DDAF (dodecylethyldimethylammonium trichloromonobromoferrate). The properties of this system are contrasted with the anionic type of surfactant and surfactant ionic liquids (SAILs) based on an imidazolium ion. Their efficiency in stabilizing a system consisting of reduced graphene oxide (RGO) and nanofibrillated kenaf cellulose was characterized through four-point probe electrical conductivity measurements. Raman spectroscopy and field emission scanning electron microscopy (FESEM) were used to investigate the morphology and dispersion quality of RGO inside the cellulose matrix. The stability of the RGO dispersions was analyzed using zeta potential measurement, giving a value of |18-32| mV for the cationic moieties and |36-59| mV for the anionic ones. Small-angle neutron scattering (SANS) was used to study the aggregation behavior of the stabilizers in an aqueous system and the RGO dispersion. The results point to a more significant effect from the addition of π-conjugated imidazolium moiety (a 5-order-of-magnitude conductivity enhancement) than from the addition of a metal moiety (FeCl₄^-) to the headgroup of the cationic compounds (a 3-order-of-magnitude enhancement).