13378 J. Phys. Chem. B, Vol. 108, No. 35, 2004
Steel et al.
about solvent orientation and conformation at liquid/liquid
interfaces will allow further refinement of models of interfacial
solvation.
to correlate with free volume within the organic phase. These
findings agree well with predictions from molecular dynamics
simulations predicting that interfacial solvent polarity should
scale with a solute’s solvent accessible area. Ongoing studies
will continue to explore the relationship between solvent
molecular structure and interfacial width.
2. Linear Alkanes. Similar to the cyclic alkanes studied, one
of the linear alkanes (octane) created a sharper interface than
the other (hexadecane). The spectra in Figures 5 and 6 indicate
that solvent polarity converges from an intermediate polarity
to that of the bulk alkane more abruptly at the water/octane
interface than at the water/hexadecane interface. We begin by
noting that Schlossman and co-workers examined a number of
water/n-alkane interfaces using X-ray reflectivity to measure
the density profile the interfacial region. Their work focused
on linear alkanes and found that as alkane chain length increased,
the interfacial width increased. Although the widths reported
in these scattering studies measure a different physical property
Acknowledgment. This work was supported by the Research
Corporation (RI0362) and the National Science Foundation
through its CAREER Program (CHE0094246).
References and Notes
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(
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For the data shown in Figures 5 and 6, differences in solvent
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Å , and that of octane is 271 Å . Obviously, hexadecane is larger
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V. Conclusion
(
We have used molecular rulers to probe solute excitation at
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The data suggest that all these interfaces are sharp, featuring
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