Temperature Dependence of Size and Polydispersity in a Three-Component Microemulsion Observed by Small-Angle Neutron Scattering
The temperature dependence of the size and polydispersity of the water core in a three-component microemulsion consisting of decane + AOT + D2O has been observed by small-angle neutron scattering. At each temperature, as a molar ratio, X. (D2O/[AOT], is varied from 8% to 49%, a linear increase in the radius is observed from about 25 Å to 90 Å. The extrapolated value of the radius at vanishing water concentration is non-zero, indicating substantial water penetration into the charged head-group region of the inverted micelle. From the slope and extrapolated radius of this line we can deduce the effective area and volume occupied by the hydrated head group at each temperature. The polydispersity in size is appreciable even at room temperature, and it increases steadily as the temperature is raised. The Q-dependence of the intensity distribution does not follow the Ornstein-Zernike form, but instead it can be well described as scattering from a collection of polydispersed spheres as the critical point (37°C for 6% D20) is approached.