Influence of Pressure on the Size of Free Volumes in Some Waxes

Positron lifetime spectra were measured as a function of pressure for multicomponent mixtures of alkanes with an average carbon chain length of 19 atoms, and a varying width of length distribution. The range of rotator phase broadens with increasing the wax component distribution. When the number of wax components was five or more, we have observed the coexistence of rotator-rigid phases. The results of analysis of high statistics positron annihilation lifetime spectra by MELT program speaks in favour of an existence (in that range) of a single broad component, rather than two components corresponding to the separate rigid and rotator phases. In the mixtures of alkanes, the inter-lamellar gap size increases significantly due to the presence of various chain lengths of the components forming the mixture. For all investigated waxes the pressure of 360 MPa was sufficient to reduce the gap width to that one observed in pure alkanes.