The size was more dependent on the combined effect of PVA concentration and volume of internal to external phase rather than on their individual effect as such.
As the smaller particles are formed the surfactant present in the external phase will coat and stabilize the particles.
As mentioned earlier, the increase in the viscosity due to high PVA concentration and insufficient agitation due to increase in the external phase volume reduces the effect of homogenization speed.
Also presence of higher external phase volume would help in reducing the steric hindrance of PVA on PLGA and reduces the cavitation effect of PVA.
As surfactants, SPAN 80 (Sorbitan monooleate, ICI Americas) was used as the lipophilic surfactant for the preparation of the primary W1/O emulsion and TWEEN 80 (Sorbitan monooleate with poliethylene oxide, ICI Americas) was used as the hydrophilic surfactant for the external phase. As the electrolyte, NaCl (Riedel de Haen) was used as received.
The initial concentration of salt (NaCl) in the inner droplets was varied, being the external phase pure water with a non-ionic surfactant of extremely low conductivity (Tween 80).
The breaking percentage was calculated as the conductivity measured in a given time (Gt) divided by the conductivity the external phase would have if all the salt were liberated (G):
It should be noted that for the 0.5% curve the initial concentration of salt in the inner droplets is of 5g/l and zero for the external phase. These calculations were made measuring the final salt concentration by conductimetry and the final external volume phase (W2), and performing a mass balance of the salt.