Molecular pore size characterization within chitosan biopolymer using positron annihilation lifetime spectroscopy

Positron annihilation lifetime spectroscopy has been used to study a chitosan biopolymer, to which nanoclay has been added, and the effect of water absorption and cross-linking on the microporosity. All measurements were conducted at room temperature. The free volume size of the biopolymer samples was obtained based on the ortho-positronium lifetime, and the relative concentration of free volume cavities was measured by the ortho-positronium intensity. Using the PALS technique, effects of hydration were observed as a reduction in the measured pore size. Similarly, the cross-linked samples exhibited an increase in intensity of the smallest pores commensurate with the SEM observations.