Tese: Rheology of functionalized graphene suspensions in a model yield stress fluid
Aluno(a) : Lorena Rodrigues da Costa MoraesOrientador(a): Monica Naccache
Área de Concentração: Termociências
Data: 07/06/2021
Link para tese/dissertação: https://doi.org/10.17771/PUCRio.acad.54659
Resumo: This work investigates the impact of functionalized graphene suspensions on the rheology of a Carbopol aqueous dispersion. The graphene derivatives used were graphene oxide (GO) and amino-functionalized graphene oxide (AFGO). The variation of the functionalized graphene concentration and oxidation was evaluated and related with the suspensions rheological behavior. GO nanosheets were produced from synthesis of graphite oxide (GrO) by modified Hummers method, and they were characterized by XRD, Raman,TGA, FTIR, XPS, TEM and AFM techniques. The GO was functionalized with triethylenetetramine by microwave assisted reaction to produce the AFGO, which was characterized by TGA and XPS techiniques. The rheological behavior of these suspensions was characterized by oscillatory and steady-state flow experiments and zeta potential characterized the suspensions colloidal aspects. The GO structure characterization shows that oxygenated functional groups were incorporated in its graphitical surface. GO oxidized for 96 hours (GO 96 h) showed higher interplanar distance and also presented fewer layers when compared with GO oxidized for 2 hours (GO 2 h). The AFGO characterization points out that aminated groups were covalently attached to the GO nanosheets and the GO with a higher oxidation degree produced an AFGO with higher amination level. All synthesized nanosheets are highly stable when suspended at neutral media. The functionalized graphene suspensions were well modeled by the Hershel-Bulkley equation. The increase of the nanosheets concentration in the suspensions impairs the level of fluid structure and leads to a decrease in viscosity, yield stress, and elasticity. The GO 96 h promoted a lower decrease in viscosity, yield stress and elasticity than the GO 2 h suspension. In the case of AFGO, the greater amination degree can lead to a more pronounced drop in the suspension rheological properties. For the suspension with a higher concentration of GO 96 h, it was observed the appearance of hysteresis at low shear rates. These results show that small changes in the graphene functionalized nanosheets surface can significantly influence the rheological responses of a non-Newtonian fluid.