A model for cylindrical nanoporosity based on single positron annihilation

A semiempirical positron stationary Quantum Model was developed to study nanoporosity in solid porous materials, such as silica gels. The cylindrical well potential is considered and its geometric parameters are related to the Positron Annihilation LifeTime Spectroscopy measurements (PALS). An alternative novel method to determine free volume sizes in solid materials was developed. The free volume equations of this new model were then compared to the well-known and widely utilized Spherical Free Volume Model (SFVM) and remarkable differences were found. A strong variation of the free volume size-positron lifetime relation with the geometry involved is observed as well as a strong dependence on the electron layer thickness parameter ΔR with the nature of the material.