Molecular motions in sucrose-PVP and sucrose-sorbitol dispersions: I. Implications of global and local mobility on stability

Sisir Bhattacharya, Raj Suryanarayanan

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


Purpose:To characterize molecular mobility by dielectric spectroscopy and determine the effect of additives on α-and β-relaxation times in amorphous sucrose solid dispersions. Methods:Sucrose was co-lyophilized with either PVP or sorbitol. The lyophiles were subjected to dielectric spectroscopy and differential scanning calorimetry. Results: The additives did not have an appreciable effect on the calorimetric Tg. However, dielectric spectroscopy revealed pronounced effects on global mobility (α-relaxation) , which correlated with the crystallization tendency of sucrose. The systems were characterized by two β-relaxations, and the relaxation times as well as their temperature dependence were influenced by the additive. Although sorbitol acted as a plasticizer of sucrose with respect to global mobility, it antiplasticized sucrose in terms of local motions. PVP, on the other hand, acted as an anti-plasticizer with respect to both global and local mobility. The slower β-relaxation in amorphous sucrose was found to correlate with the α-relaxation and was identified as the Johari-Goldstein relaxation. Conclusions:Amorphous systems with identical calorimetric Tg could have significantly different mobility and physical stability as revealed by dielectric spectroscopy. Additive effect on global mobility cannot be a predictor of the effects on local mobility. Additives could also be used to inhibit local mobility.

Original languageEnglish (US)
Pages (from-to)2191-2203
Number of pages13
JournalPharmaceutical research
Issue number9
StatePublished - Sep 2011


  • Amorphous
  • Dielectric spectroscopy
  • Global and local mobility
  • Solid dispersions
  • Sucrose


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