Quasi-elastic light scattering in polymer-containing microemulsion

Quasi-elastic light scattering (QELS) was performed in dilute water in oil microemulsion stabilized by AOT surfactant. The water-soluble polyethylene oxide (PEG) with low molecular weight (8000) added to the microemulsion seems to be confined within the aqueous microphase, since PEO is insoluble in oil (n-heptane). The measurements by QELS of diffusion coefficient, at dilute concentrations, allow determination of the size of the droplets. The phase diagram of the microemulsion undergoes remarkable changes on addition of the polymer. The results show that at fixed R (water/surfactant ratio) the droplets decrease their size as the concentration of polymer increases. This occurrence can be related to the change of interface interaction due to the addition of polymer. Moreover, the hydrodynamic radius, near the critical composition, shows critical behaviour, as a function of the reduced temperature, which seems not to be affected by the polymer addition.