Effect of Added C4-Alcohols on the Structure of Microemulsion Droplets Measured by Small-Angle Neutron Scattering.

The role of C4-alcohols (n-butanol, 2-butanol and tert-butanol) in four component microemulsions is studied using neutron scattering. These microemulsions are dispersions of nanoscale droplets consisting of a core of water surrounded by a surfactant-stabilized shell. The particles are suspended in an oil (octane) continuum. The addition of a co-surfactant, such as a short-chain alcohol, modifies the droplet size and structure, as well as the rigidity of the surrounding shell. In this work, we investigate water-in-oil microemulsions employing small-angle neutron scattering (SANS) experiments performed at the NIST Center for Neutron Research. Using this technique, it is possible to probe structure on the nanometer scale and extract information rele\ant to the structure of our system. The SANS data is analyzed with a model sensitive to the overall shape, size, polydispersity, and the internal structure of the dispersed droplets. In addition, the model also incorporates corrections for droplet shape fluctuations and smearing resolution associated with the SANS instrument. This work focuses primarily on the effect of the tert-butanol structural isomer on the microemulsion system. However, data from the n-butanol and 2-butanol cases is included as well for purposes of comparison with other research groups. For all C4 isomers examined, when increasing the alcohol content, the size of the droplets decreases, whereas the polydispersity and shape fluctuations of the droplets increase