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Perfluorinated Surfactant Chain-Length Effects on Sonochemical Kinetics

Campbell, Tammy Y. and Vecitis, Chad D. and Mader, Brian T. and Hoffmann, Michael R. (2009) Perfluorinated Surfactant Chain-Length Effects on Sonochemical Kinetics. Journal of Physical Chemistry A, 113 (36). pp. 9834-9842. ISSN 1089-5639.

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The sonochemical degradation kinetics of the aqueous perfluorochemicals (PFCs) perfluorobutanoate (PFBA), perfluorobutanesulfonate (PFBS), perfluorohexanoate (PFHA), and perfluorohexanesulfonate (PFHS) have been investigated. Surface tension measurements were used to evaluate chain-length effects on equilibrium air−water interface partitioning. The PFC air−water interface partitioning coefficients, K_(eq)^(PF), and maximum surface concentrations, Γ_(max)^(PF), were determined from the surface pressure equation of state for PFBA, PFBS, PFHA, and PFHS. Relative K_(eq)^(PF) values were dependent upon chain length K_(eq)^(PFHS) ≅ 2.1K_(eq)^(PFHA) ≅ 3.9K_(eq)^(PFBS) ≅ 5.0K_(eq)^(PFBA), whereas relative Γ_(max)^(PF) values had minimal chain length dependence Γ_(max)^(PFHS) ≅ Γ_(max)^(PFHA) ≅ Γ_(max)^(PFBS) ≅ 2.2Γ_(max)^(PFBA). The rates of sonolytic degradation were determined over a range of frequencies from 202 to 1060 kHz at dilute (<1 μM) initial PFC concentrations and are compared to previously reported results for their C8 analogs: perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA). Under all conditions, the time-dependent PFC sonolytic degradation was observed to follow pseudo-first-order kinetics, i.e., below kinetic saturation, suggesting bubble−water interface populations were significantly below the adsorption maximum. The PFHX (where X = A or S) sonolysis rate constant was observed to peak at an ultrasonic frequency of 358 kHz, similar to that for PFOX. In contrast, the PFBX degradation rate constants had an apparent maximum at 610 kHz. Degradation rates observed for PFHX are similar to previously determined PFOX rates, k_(app,358)^(PFOX) ≅ k(app,358)^(PFHX). PFOX is sonolytically pyrolyzed at the transiently cavitating bubble−water interface, suggesting that rates should be proportional to equilibrium interfacial partitioning. However, relative equilibrium air−water interfacial partitioning predicts that K_(eq)^(PFOX) ≅ 5K_(eq)^(PFHX). This suggests that at dilute PFC concentrations, adsorption to the bubble−water interface is ultrasonically enhanced due to high-velocity radial bubble oscillations. PFC sonochemical kinetics are slower for PFBS and further diminished for PFBA as compared to longer analogs, suggesting that PFBX surface films are of lower stability due to their greater water solubility.

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Hoffmann, Michael R.0000-0001-6495-1946
Additional Information:Copyright © 2009 American Chemical Society. Received: April 1, 2009; Revised Manuscript Received: June 27, 2009. Publication Date (Web): August 18, 2009. Research support and donation of analytical equipment from the 3M Environmental Laboratory is gratefully acknowledged. We also thank Jie Cheng and Dr. Hyungwoong Park for their useful discussions and Dr. Nathan Dalleska of the Environmental Analytical Center for analytical assistance.
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Issue or Number:36
Record Number:CaltechAUTHORS:20090923-143135227
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Official Citation:Perfluorinated Surfactant Chain-Length Effects on Sonochemical Kinetics Tammy Y. Campbell, Chad D. Vecitis, Brian T. Mader, Michael R. Hoffmann The Journal of Physical Chemistry A 2009 113 (36), 9834-9842
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:16020
Deposited By: George Porter
Deposited On:06 Oct 2009 17:53
Last Modified:03 Mar 2020 13:01

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