Percolation in concentrated water-in-carbon dioxide microemulsions
The phase behavior and electrical conductivity of water-in-carbon dioxide (W/C) microemulsions are reported over a range of temperatures (5--65 C), pressures (100--450 bar), and droplet volume fractions ({phi} = 0.0347-0.483) at a constant water-to-surfactant molar ratio (W{sub o}) of 12.5. A {phi} of 0.483 is a 5-fold increase over those reported previously. A critical point is observed at a droplet volume fraction of approximately 0.12, at which the single-phase microemulsion splits into two microemulsion phases of similar volume upon lowering the pressure (upper critical solution pressure). At low temperatures, a lower critical solution pressure is also observed upon increasing the pressure. Both of the critical solution pressures result from an increase in the attractive interdroplet interactions; consequently, pressure has little effect on the conductivity in the one-phase region. The conductivity increases nearly 3 orders of magnitude with changes in the droplet concentration or temperature. Scaling analysis of the conductivity data supports a dynamic percolation model, whereby the attractive interdroplet interactions form clusters of discrete droplets with rapid charge transport.
- Research Organization:
- Univ. of Texas, Austin, TX (US)
- Sponsoring Organization:
- National Science Foundation (NSF); USDOE
- DOE Contract Number:
- FG03-96ER14664
- OSTI ID:
- 20075919
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 104, Issue 18; Other Information: PBD: 11 May 2000; ISSN 1089-5647
- Country of Publication:
- United States
- Language:
- English
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