Induced structural changes at aliphatic hydrocarbon-graphite interfaces

E. P. Gilbert*, P. A. Reynolds, J. W. White

*Corresponding author for this work

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    9 Citations (Scopus)


    Small-angle X-ray scattering and quasielastic neutron scattering have been used to investigate the structures and phase behaviour of normal alkanes with carbon number n for 10≤n≤20 when adsorbed on Papyex. Ordering of the hydrocarbon molecules occurs at the interface, and this surface crystalline structure persists at least 30 °C above the melting temperature of the bulk crystalline phase. The surface-adsorbed structure is a lamellar arrangement different from the bulk phase. Below the bulk melting point, Tm, and for alkanes with even n, two distinct diffraction peaks are observed in the small-angle region, one associated with the bulk phase and the other with the surface structure. For alkanes with odd n, only one peak is observed below Tm; above Tm a significant reduction in peak intensity is found, indicating melting of the bulk, but a peak remains. The peak intensity at T = Tm increases with n, indicating increasing surface stabilization with increasing chain length. The separation between Tm and the temperature at which the diffracted intensity is greatest decreases as n increases and the values of the former agree well with values associated with a metastable phase transition observed previously by Schaerer. A comparison of the QENS from bulk C16H34 and C16H34 adsorbed on Papyex below Tm indicates no significant difference in elastic peak broadening. Above Tm, the chains are shown to undergo translational motion. The lower bound to the rotational correlation time is estimated to be ca. 3 ns, which is some two orders of magnitude larger than the typical alkane rotator phase.

    Original languageEnglish
    Pages (from-to)81-100
    Number of pages20
    JournalColloids and Surfaces A: Physicochemical and Engineering Aspects
    Issue number1
    Publication statusPublished - 15 Oct 1998


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