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Title: Buffering the aqueous phase pH in water-in-CO{sub 2} microemulsions

Abstract

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 andmore » pressure on pH values are negligible.« less

Authors:
; ; ; ; ;  [1];  [2]
  1. Univ. of Texas, Austin, TX (United States). Dept. of Chemical Engineering
  2. Univ. of East Anglia, Norwich (United Kingdom). School of Chemical Sciences
Publication Date:
Sponsoring Org.:
National Science Foundation, Washington, DC (United States); USDOE, Washington, DC (United States)
OSTI Identifier:
682110
DOE Contract Number:  
FG03-96ER14664
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical
Additional Journal Information:
Journal Volume: 103; Journal Issue: 27; Other Information: PBD: 8 Jul 1999
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; PH VALUE; BUFFERS; MICROEMULSIONS; WATER; CARBON DIOXIDE; AMMONIUM COMPOUNDS; POLYETHYLENE GLYCOLS

Citation Formats

Holmes, J D, Ziegler, K J, Audriani, M, Lee, Jr, C T, Bhargava, P A, Johnston, K P, and Steytler, D C. Buffering the aqueous phase pH in water-in-CO{sub 2} microemulsions. United States: N. p., 1999. Web. doi:10.1021/jp990745v.
Holmes, J D, Ziegler, K J, Audriani, M, Lee, Jr, C T, Bhargava, P A, Johnston, K P, & Steytler, D C. Buffering the aqueous phase pH in water-in-CO{sub 2} microemulsions. United States. https://doi.org/10.1021/jp990745v
Holmes, J D, Ziegler, K J, Audriani, M, Lee, Jr, C T, Bhargava, P A, Johnston, K P, and Steytler, D C. 1999. "Buffering the aqueous phase pH in water-in-CO{sub 2} microemulsions". United States. https://doi.org/10.1021/jp990745v.
@article{osti_682110,
title = {Buffering the aqueous phase pH in water-in-CO{sub 2} microemulsions},
author = {Holmes, J D and Ziegler, K J and Audriani, M and Lee, Jr, C T and Bhargava, P A and Johnston, K P and Steytler, D C},
abstractNote = {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.},
doi = {10.1021/jp990745v},
url = {https://www.osti.gov/biblio/682110}, journal = {Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical},
number = 27,
volume = 103,
place = {United States},
year = {1999},
month = {7}
}