A Rheological Study of the Structure of Microemulsions
Microemulsions are optically isotropic, stable mixtures of water, oil and surfactant(s) (mixture). Their internal structure can be characterized with length scales pertaining to the sizes of domains of the dispersed phase (e.g. oil) in the continuous phase (e.g. water). The dispersion occurs because of the presence of surfactant(s) at the oil-water interface.
The morphology and pertaining length scales are subject of research. As structure one can think of droplets, flexible rods and so-called bicontinuous structures.
Rheologically the microemulsions have been investigated with harmonic shear experiments to determine the complex viscosity η*. Between 102 and 2 105 Hz all measurements of η* show a transition of purely viscous to viscous and elastic behaviour. Each transition has been characterized with a relaxation time and relaxation strength. For the interpretation of these relaxation phenomena a few models are available. The measurements have been interpreted such that a consistent picture has been obtained for the various structures of the investigated microemulsions, in the present case a transition from spherical to rod-shaped droplets.
KeywordsComplex Viscosity Relaxation Phenomenon Rheological Study Spherical Droplet Relaxation Strength
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