Effects of pH on dynamics and rheology during association and gelation via the Ugi reaction of aqueous alginate |
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Authors: | Huaitian Bu Bo Nyström |
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Institution: | Department of Chemistry, University of Oslo, P.O. Box 1033, N-0315 Oslo, Norway |
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Abstract: | Effects of solution pH on the physical properties of a semidilute aqueous alginate solution without cross-linker agent and during gelation via the Ugi multicomponent condensation reaction at a fixed cross-linker concentration have been investigated. Both rheology and turbidity results on the alginate solution without cross-linker revealed enhanced associations at low pH. In the course of the cross-linker reaction, the time of gelation is shortest at pH = 3.5 and at pH values above 3.8 no gel is formed but only a viscosification of the solution is observed. The turbidity during the cross-linking reaction rises as the pH increases from 3.5 to 5. Furthermore, the initial change of the turbidity in the course of the cross-linking process is more pronounced at higher pH. The dynamic light scattering (DLS) results of the reaction mixture at pH = 4.0 (ergodic features at this condition) show that the chain relaxation is slowed down as the reaction proceeds. The effect of pH on the kinetics of the Ugi reaction is discussed. |
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Keywords: | Alginate pH effect Ugi cross-linking reaction Gelation Rheology Dynamics |
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