Early stages of gelation in gelatin solution detected by dynamic oscillating rheology and nuclear magnetic spectroscopy.
In: European Polymer Journal, Jg. 43 (2007) ; Nr. 4, S. 1480-1486
Zeitschriftenaufsatz / Fach: Chemie
This study focuses on the early stages of the gelation of an aq. type A (pig skin) gelatin soln. The thermo-reversible mono and triple helix formation was obsd. by rheol. and proton NMR relaxation measurements. At high temps. (T > 330 K), gelatin mols. form flexible random coils of small hydrodynamic radius, the elastic modulus of the soln. is relatively low. On decreasing the temp. (330-320 K), mono helix formation begins, connected with an increase of the storage modulus and the hydrodynamic radius. The absence of a significant concn. dependence of this early variation of the modulus indicates the intramol. nature of this structural change. The simultaneous decrease of the spin-spin relaxation times of the 1H signals of certain aminoacids confirms its effect on the mol. mobility. As this affects esp. the signals of arginine and lysine, we conclude that these basic aminoacids play a significant role in forming the intramol. interactions. The formation of a three-dimensional network occurs at a point at which the viscosity begins to increase rapidly near the gel point (T < 320 K). This process is clearly dominated by intermol. interactions, as the slope and the starting point of the rapid increase significantly depends on the concn.