The performance of the nanofiber as reinforcing agent is also
associated with other features such as surface charge (zeta potential).
According to Tholstrup Sejersen et al. (2007), nanosized particles
should have high zeta potential, so that the colloidal
suspension can resist aggregation, to increase its degree of
dispersion in the composite. In neutral water, all the CNFs suspensions
exhibited negative zeta potential; the values were 16.1
and 25.7 mV for the nanoparticles obtained by CT and ET,
respectively. Bondeson and Oksman (2007) reported that hydrolysis
with sulfuric acid elicited electrostatic repulsion between
nanofibers in suspension, and that this process introduced natural
sulfate groups into the nanofiber surface. However, ET led to CNFs
with the highest zeta potential, showing that the resulting nanofibers
were more electrically stable. Higher electrostatic repulsion
existed between the fibers in this case, providing enough surface
charges to stabilize the suspension. CNFs from CT, on the other
hand, were more likely to aggregate. This could jeopardize their
ability to act as reinforcing agents in polymer matrices.