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J. Phys. Chem. B 2004, 108, 13370-13378
Solvent Polarity across Weakly Associating Interfaces William H. Steel,† Yuen Y. Lau,† Carmen L. Beildeck,† and Robert A. Walker*,†,‡ Department of Chemistry and Biochemistry, UniVersity of Maryland, College Park, College Park, Maryland 20742 ReceiVed: January 13, 2004; In Final Form: June 16, 2004
Molecular ruler surfactants, solvatochromic probes of solvent polarity, have been used to examine changes in solvent polarity across weakly associating liquid/liquid interfaces. The water/alkane interfaces were formed between an aqueous subphase and either cyclic (cyclohexane and methylcyclohexane) or linear (octane and hexadecane) alkanes. Resonance-enhanced second-harmonic generation was used to collect effective excitation spectra of species adsorbed to these interfaces. As surfactants lengthened, the surfactant probe sampled an increasingly nonpolar environment as evidenced by an excitation wavelength that shifted toward the alkane limit. Data suggest that all four water/alkane interfaces are molecularly sharp (
