Buffering the aqueous phase pH in water-in-CO{sub 2} microemulsions
- Univ. of Texas, Austin, TX (United States). Dept. of Chemical Engineering
- Univ. of East Anglia, Norwich (United Kingdom). School of Chemical Sciences
Water-in-oil (w/o) microemulsions have been exploited for use in a wide range of applications, including chemical and enzymatic reactions, protein and metal extraction, and the production of nanoparticles. Microemulsions are attractive systems for studying such applications because they have the ability to function as a universal solvent medium by solubilizing high concentrations of both polar and apolar molecules within their dispersed aqueous and continuous oil phases, respectively. The addition of organic and inorganic buffers to nanometer size water-in-CO{sub 2} microemulsion droplets stabilized by ammonium perfluoropolyether (PFPE-NH{sub 4}) results in an increase in pH from 3 to values of 5--7. The effects of temperature, pressure, buffer type, buffer concentration, ionic strength, and CO{sub 2} solubility on the pH inside water-in-CO{sub 2} microemulsions and on biphasic water-CO{sub 2} systems were measured by the hydrophilic indicator 4-nitrophenyl-2-sulfonate and were predicted accurately with thermodynamic models. In both systems, modest buffer loadings result in a steep pH jump from 2.5 pH units. Further increases in pH require large amounts of base to overcome buffering due to the carbonic acid-bicarbonate equilibrium. A pH approaching neutrality was obtained in w/c microemulsions with approximately 1.5 mol kg{sup {minus}1} NaOH. At high buffer loadings, the effects of temperature and pressure on pH values are negligible.
- Sponsoring Organization:
- National Science Foundation, Washington, DC (United States); USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG03-96ER14664
- OSTI ID:
- 682110
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 103, Issue 27; Other Information: PBD: 8 Jul 1999
- Country of Publication:
- United States
- Language:
- English
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