Zeta potential and particle size measurements
PEC zeta potential and the size of the dispersed polymer nanoparticles were measured using the Zetasizer Nano-ZS (Malvern®, Worcestershire, UK). Three independent zeta potential measurements at various pH values were carried out on each sample of 0.1% (w/v) PEC aqueous solution. 1.0 mL of PEC solution was introduced in the measurement vessel. Temperature was set at 25 °C, applied voltage was 200 mV and duration of each analysis was approximately 10 min. The mean hydrodynamic diameter of particles was also determined as a function of pH with the Zetasizer Nano-ZS by using dynamic light scattering. The device uses a helium-neon laser of 4 mW output power operating at the fixed wavelength of 633 nm (wavelength of laser red emission). All the results were reported as mean ± standard deviation. PEC zeta potential was also measured in the presence of increasing concentrations of either calcium ions or polyamines both without and with glycerol (30%, w/w PEC) addition.