Document Detail

Charge-based forces at the Nafion-water interface.
MedLine Citation:
PMID:  23311934     Owner:  NLM     Status:  MEDLINE    
Interfacial water lying next to hydrophilic surfaces has been shown to be spectroscopically, mechanically, and electrically distinct from bulk water. Interfacial water has also been shown to exclude negatively and positively charged microspheres and has thus become known as the "exclusion zone". Measurements have demonstrated that exclusion zones exhibit a negative electrical potential on the order of -100 mV relative to bulk water, with a corresponding distribution of positive protons in the bulk water region beyond the exclusion zone. This separation of charge is hypothesized to create an electrostatic force between the exclusion zone and the proton-enriched zone beyond. To test this hypothesis, a hydrophilic Nafion ring was attached to the tip of a deflectable ribbonlike force sensor. The sensor was designed to obstruct the flow of protons from one side of the lever to the other, so that any proton-based force would remain unilateral. pH-sensitive dye measurements confirmed that the protons were largely confined to one side. When the lever assembly was exposed to water, the sensor deflected toward the protons. Over a period of 20 min, deflection amounted to approximately 20 μm, corresponding to a force of approximately 22 μN. Hence, electrostatic forces are confirmed. If exclusion zones exist ubiquitously at hydrophilic surfaces, including biological surfaces, then the resulting electrostatic forces may play significant roles in many biological phenomena including adhesion and protein folding.
Ronnie Das; Gerald H Pollack
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Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't     Date:  2013-02-13
Journal Detail:
Title:  Langmuir : the ACS journal of surfaces and colloids     Volume:  29     ISSN:  1520-5827     ISO Abbreviation:  Langmuir     Publication Date:  2013 Feb 
Date Detail:
Created Date:  2013-02-26     Completed Date:  2013-08-13     Revised Date:  2014-01-16    
Medline Journal Info:
Nlm Unique ID:  9882736     Medline TA:  Langmuir     Country:  United States    
Other Details:
Languages:  eng     Pagination:  2651-8     Citation Subset:  IM    
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MeSH Terms
Fluorocarbon Polymers / chemistry*
Particle Size
Surface Properties
Water / chemistry*
Grant Support
Reg. No./Substance:
0/Fluorocarbon Polymers; 059QF0KO0R/Water; 39464-59-0/perfluorosulfonic acid

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