Premium
Gel‐sol transition in gellan aqueous solutions
Author(s) -
Miyoshi Emako,
Takaya Tomohisa,
Nishinari Katsuyoshi
Publication year - 1995
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/masy.19950990110
Subject(s) - differential scanning calorimetry , aqueous solution , gellan gum , ionic bonding , materials science , transition temperature , divalent , glass transition , chemistry , polymer , crystallography , analytical chemistry (journal) , chemical engineering , polymer chemistry , organic chemistry , thermodynamics , ion , physics , superconductivity , food science , quantum mechanics , engineering
Gel‐sol transition of sodium type gellan solutions with and without salts is studied by dynamic viscoelastic measurements and differential scanning calorimetry (DSC). Mechanical spectra show that gellan aqueous solutions behave as an entangled polymer solution in the concentration range around 2 wt.‐% at temperatures >15°C and as a weak gel below this temperature. Concentrated solutions (> 3 wt.‐%) show a true gel behavior below 30°C. The two step transition is observed for 2∼3 wt.‐% gellan aqueous solutions in thermal scanning rheological (TSR) measurements; the transition at a higher temperature is attributed to a coil‐helix transition whilst the transition at a lower temperature is attributed to sol‐gel transition. The transition observed in dilute solutions of gellan is attributed to the coil‐helix transition whilst the sol‐gel transition occurs simultaneously with coil‐helix transition in more concentrated solutions (>3 wt.‐%). The sol‐gel transition temperature shifts to higher temperatures with increasing concentration of the added salts. Junction zones formed in the presence of divalent cations are far more heat resistant than those with monovalent cations judging from both DSC and TSR, however, the possibility of the formation of junction zones by covalent bonds or by ionic bonds is excluded.