Analysis methodReal time positron annihilation lifetime spectroscopy for the detection of the hydrocolloid gel-film transition of polymers

Real time positron annihilation lifetime spectroscopy was applied to study the transition from hydrogel to film in the case of two biopolymer gels (sodium alginate and Carbopol 71G) of various concentrations (3 %w/w and 0.1-1 %w/w). The transition from a polymer-in-water system to a water-in-polymer system was sensitively tracked by o-Ps lifetime values as a function of the drying time. The addition of Carbopol 71G to the sodium alginate gel modified the phase transition time and, consequently, the drying characteristics of the gel, depending on its concentration. The developed method enabled the determination of the exact time needed for the gel-film transition. This could be of impact in the course of the formulation of hydrogel polymer delivery systems and coated dosage forms.