Rheological improvement of TiO2 nanoparticles modified by dicarboxylic acids

In this research work, the improvement of the colloidal stability of titanium dioxide (TiO2) is presented by means of surface chemical modification using variable chain dicarboxylic acids such as pimelic acid (PA), glutaric acid (GA), and azelaic acid (AA). The characterization of the organic coating was carried out by transmission electron microscopy, infrared spectroscopy, and nuclear magnetic resonance. The improvement of dispersion, rheological behavior, and colloidal stability were evaluated using light techniques and mathematical rheological modeling. An improvement in the integration of modified nanoparticles was demonstrated regardless of the chain length of the organic coating. The dynamic rheological measurements of the suspensions confirmed the decrease in viscosity by two orders of magnitude (GA at low concentrations) and by an order of magnitude (when PA does not exceed 60% and AA remains at least 50% concentration), due to the decrease in the force necessary to break the agglomerates. It was found that the optimal concentrations maintain the fluidity of the suspensions studied by rheological models; supporting the behavior observed in dynamic rheological measurements. The H2O/TiO2 and H2O/GA-TiO2 suspensions show good behavior when concentrations around 30% are maintained; however, when the chain length is increased, the amount of material plays an important role, that is, there is an optimum value of around 50% for H2O/PA-TiO2 and H2O/AA-TiO2 suspensions. A change in the pseudoplastic behavior of H2O/PA-TiO2 was found when higher than optimal concentrations are used due to the increase in dipole interactions, which are manifested as an increase in viscosity. While for the suspension of H2O/AA-TiO2 as the amount of material increases, the formation of microfibers increases and induces a decrease in viscosity. The mathematical modeling of the suspensions made it possible to determine the appropriate concentration threshold to reduce the energy required to transport them.