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Small-Angle Neutron Scattering of Percolative Perfluoropolyether Water in Oil Microemulsions

Research Area: Uncategorized Year: 2010
Type of Publication: Article
Authors:
Journal: JOURNAL OF PHYSICAL CHEMISTRY B Volume: 114
Number: 11 Pages: 3855-3862
Month: March
ISSN: 1520-6106
Abstract:
A water in oil microemulsion system composed of water, surfactant, and oil, the latter two components of perfluoropolyether (PFPE) type, has been studied by small-angle neutron scattering (SANS) with the aim of knowing the microstructure Of the system and 10 have an insight oil the connection between microstructure characterization and percolation behavior. In fact. along the dilution line W/S = 11 of the Phase diagram, dielectric spectroscopy and conductivity studies revealed a dynamic percolation process taking place approaching and above the dynamic percolation threshold, leading to I system composed of droplet clusters with percolation thresholds varying with temperature from a 0.50 1 volume fraction of the dispersed phase at 9.3 degrees C to 0.205 at 32.5 degrees C. The SANS experimental spectra of this work have been studied by modeling the microemulsion droplets as adhesive hard spheres. For all of the samples, file surfactant area per Polar head has been also measured in the Porod region of the SANS spectra. Geometric and potential parameters as well as tile OSnl0tiC PI-CSSUre, the second virial coefficient, and the distance between droplets have been extracted form data as a functional of droplets concentration. At low concentration, that is, below percolation thresholds, the droplets behave as hard spheres, whereas at threshold and above, adhesion changes significantly the samples. In fact, for each temperature, the measured size increases versus Concentration from 30 to 50 A, and the area per polar head decreases correspondingly, suggesting that I process of dynamic fusion of droplets occurs in the system above threshold, that is, couples of droplets stick and unstick continuously With interdigitation of the surfactant tails.
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