Accession Number : ADA326863

Title :   Ordering of Interfacial Water Molecules at the Charged Air/Water Interface Observed by Vibrational Sum Frequency Generation.

Descriptive Note : Technical rept. 1 Jun 96-31 May 97,

Corporate Author : OREGON UNIV EUGENE DEPT OF CHEMISTRY

Personal Author(s) : Gragson, D. E. ; McCarty, B. M. ; Richmond, G. L.

PDF Url : ADA326863

Report Date : MAY 1997

Pagination or Media Count : 39

Abstract : The molecular structure and orientation of interfacial water molecules at the air/water interface in the presence of soluble cationic and anionic surfactants has been characterized. We have employed vibrational sum frequency generation (VSFG) to probe the orientation of interfacial water molecules as a function of both bulk surfactant concentration and solution ion strength. The observed ordering of interfacial water molecules is manifested by an enhancement of the OH stretching modes in the VSFG spectra. We attribute the observed enhancement to an ordering of the interfacial water molecules induced by the large electrostatic field present at these charged interfaces. From the VSFG measurements we find that both the interfacial surfactant and water molecules attain their highest degree of order at sub-monolayer concentrations. The nature of this enhancement is further explored by studying mixed (cationic and anionic) surfactant systems as well as surfactant systems at different ionic strengths.

Descriptors :   *SURFACE ACTIVE SUBSTANCES, *MOLECULAR STRUCTURE, *AIR WATER INTERACTIONS, CATIONS, SOLUTIONS(MIXTURES), MOLECULAR VIBRATION, INTERFACES, WATER, THESES, CONCENTRATION(COMPOSITION), ANIONS, ELECTROSTATIC FIELDS, HYDROXYL RADICALS.

Subject Categories : Physical Chemistry
      Miscellaneous Materials

Distribution Statement : APPROVED FOR PUBLIC RELEASE