Positronium in solid phases of n-alkane binary mixtures

•Rotator phase in even alkanes CnH2n+2 with n ⩽ 20 appears in mixed samples only.•Interlamellar gap width is the same for shorter chain alkane concentration x and 1 − x.•Excess electron trapping diminishes with broadening of alkane chain distribution Δn.

Binary mixtures of even-numbered normal alkanes CnH2n+2 and Cn+2H2n+6 with n ⩽ 18 were investigated by positron annihilation spectroscopy. Formation of the rotator phase was observed in mixed structures, while no such a phase in neat alkanes in this range of n was found. Phase diagrams for n = 18 and n = 16 are very similar to the diagrams for binary mixtures of odd-numbered alkanes. The effect of positronium formation with trapped excess electrons weakens with decreasing n, at low n values the time constant of Ps rise contains the component much shorter than 1 h.

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