The structures and rheological properties of Span 80/PEG 400/H2O niosomes are studied by using atomic force
microscopy, dynamic light scattering and rheology techniques. The niosome system at high frequency region is a
Newtonian fluid with linear viscoelasticity. The cole-cole plots at low frequency region are not semicircular and the
system is not linear viscoelastic. At a mass ratio of Span 80⁄PEG 400, the viscosity, relaxation time, elastic and loss
moduli of the system decrease with water content but increase with PEG 400 content. With the increase of oscillatory
shear frequency, the storage modulus increases but the loss modulus first increases and then decreases.