Molecular motions in sucrose-PVP and sucrose-sorbitol dispersions - II. Implications of annealing on secondary relaxations

Purpose: To determine the effect of annealing on the two secondary relaxations in amorphous sucrose and in sucrose solid dispersions.

Methods: Sucrose was co-lyophilized with either PVP or sorbitol, annealed for different time periods and analyzed by dielectric spectroscopy.

Results: In an earlier investigation, we had documented the effect of PVP and sorbitol on the primary and the two secondary relaxations in amorphous sucrose solid dispersions (1). Here we investigated the effect of annealing on local motions, both in amorphous sucrose and in the dispersions. The average relaxation time of the local motion (irrespective of origin) in sucrose, decreased upon annealing. However, the heterogeneity in relaxation time distribution as well as the dielectric strength decreased only for β₁- (the slower relaxation) but not for β₂-relaxations. The effect of annealing on β₂-relaxation times was neutralized by sorbitol while PVP negated the effect of annealing on both β₁- and β₂-relaxations.

Conclusions: An increase in local mobility of sucrose brought about by annealing could be negated with an additive.