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Role of Microscopic Phase Separation in Gelation of Aqueous Gelatin Solutions

Using a unique home-made cell for four-contact impedance spectroscopy of conductive liquid samples, we establish the existence of two low frequency conductivity relaxations in aqueous solutions of gelatin, in both liquid and gel state. A comparison with diffusion measurements using pulsed field gradient NMR, and circular dichroism spectroscopy, shows that the faster relaxation process is due to gelatin macromolecule self-diffusion. This single molecule diffusion is mostly insensitive to the macroscopic state of the sample, implying that we have a clear separation of gelatin molecules into a free and network-bound phase. Scaling relations for the self-diffusion indicate that the gelation process is not a percolative phenomenon, but is caused by aggregation of triple helices into a system-spanning fibre network.

impedance spectroscopy; gelation; pulsed field gradient NMR; circular dichroism spectroscopy

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