Free volumes studies in Thymoquinone and Carvone β-cyclodextrin nanoparticles by positron annihilation lifetime spectroscopy

Positron annihilation lifetime spectroscopy is used to study free volume in beta-cyclodextrin with the encapsulation of thymoquinone and S-carvone, in samples covering the guest to host fraction range from 1:0.1 to 1:1. The results clearly indicate the presence of long lifetime components related to Ps-formation. Although the behavior of the two guests is different, in both cases the results indicate the formation of 1:1 cyclodextrin inclusion compounds. Data show that the addition of carvone to beta-cyclodextrin results in a decrease of the o-Ps lifetime corresponding to a reduction of the average radius of cavities from 2.41 angstrom to 2.29 angstrom, whereas the addition of thymoquine decreases the radius from 2.57 angstrom to 2.35 angstrom. In turn, the intensity varied from 20.55 to 19.20% and from 20.83 to 0.41%, respectively.