Characterization of gelation of aqueous pectin via the Ugi multicomponent condensation reaction

Turbidity and rheological features during gelation of semidilute solutions of pectin via the Ugi multicomponent condensation reaction have been investigated at different polymer and cross-linker concentrations at ambient temperature. The gelation time of the system decreased with increasing polymer and cross-linker concentrations. At the gel point, a power law frequency dependence of the dynamic storage modulus (G' similar to omega(n)') and loss modulus (G'' similar to omega(n)'') was observed with n'= n''= n. The value of the power law exponent is about 0.6 similar to 0.7 for all the gelling systems, which is close to that predicted (0.7) from the percolation model. The elastic properties of the gels continue to grow over a long time in the post- gel region, and a solidlike response is observed at later stages during the gelation process. The turbidity of the gelling system is higher as the polymer and cross- linker concentrations rise, but the turbidity is virtually unaffected during an extended time after the formation of the incipient gel. It was demonstrated that polymer and cross- linker concentrations could be utilized to tune the physical properties, such as transparency and viscoelasticity, of the Ugi hydrogels.