Temperature dependence of nanoholes free volume in polypropylene glycols

摘要

Estimation of the free volume fraction in disordered systems can be obtained by combining specific volume measurements with positron annihilation lifetime data. Usually, nanoholes are supposed to expand isotropically under, e.g., temperature increase. This letter shows results for a homologous series of polypropylene glycols which are discussed in terms of anisotropic nanoholes expansion, ascribed to constraints on the molecular motions. A relationship between volume and unconstrained, average size of the cavity is obtained in the form of a power law with a noninteger exponent.