Surfactant headgroup orientation at the air/water interface.
We have used vibrational sum-frequency spectroscopy to provide the first measurement of the spectrum and orientation of the polar headgroup of a charged alkyl surfactant at the air/water interface. Sum-frequency spectra of sodium dodecyl sulfate (SDS) are used to arrive at all participating elements of the second-order susceptibility tensor. We use these chi(2) elements, together with calculated values of the hyperpolarizability, to determine the tilt of the S-O bond attached to the alkyl chain and the twist of the S-O-C plane. Thus, a full characterization of the orientation of the surfactant headgroup has been achieved. This is the first demonstration of the feasibility of sum-frequency measurements of sulfate modes in the 1100 cm-1 region, opening possibilities for future investigations of surfactant behavior in this spectral region at aqueous and solid interfaces.
Department of Chemistry, University of Oregon, Eugene, Oregon 97403, USA.
Dennis K
DK
Hore
Daniel K
DK
Beaman
Geraldine L
GL
Richmond
D000388:Air; D002244:Carbon / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D013055:Spectrophotometry, Infrared; D013455:Sulfur / Q000737:chemistry; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
D013501:Surface-Active Agents; D014867:Water; D012967:Sodium Dodecyl Sulfate; D013455:Sulfur; D002244:Carbon; D010100:Oxygen