The structure of the Ca--alginate junction zones was investigated with X-ray scattering on gels prepared with different methods. Fiber diffraction reveals the popular egg-box model may not be the only possible structure for the junction zones. The (001) reflection, which should be extinguished due to 2/1 helical conformation in the egg-box model, was observed. This was further confirmed by the measurements on Ca--alginate gel beads prepared at different pH where large pieces were formed through a relatively slow process, which leads to a higher crystallinity and a more perfect ordering. The results suggest a 3/1 helical conformation is more proper for Ca--alginate gels formed slowly. This does not exclude the possibility for the 2/1 helical conformation in fast gelatinized Ca--alginate in which the 2/1 helix is a metastable form. Comparing the X-ray scattering results of the fresh, dehydrated, and rehydrated gels, a reversible aggregation of junction zones is found during dehydration and rehydration. The different stabilities of initial bonds and bonds formed during drying are speculated to be the contribution of MG block or short G blocks in the junction zones.

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Citation for published version (APA): Brinksma, J., Feringa, B. L., Kellogg, R. M., Vreeker, R., & van Esch, J. H. (2000). Rheology and thermotropic properties of bis-urea-based organogels in various primary alcohols. Langmuir, 16(24), 9249 -9255. https://doi.org/10.1021/la000839s Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. The thermotropic and viscoelastic properties and the structure of thermoreversible organogels composed of enantiomerically pure trans-1,2-bis(3-dodecylureido)cyclohexane (1) and primary alcohols, i.e., propanol, butanol, hexanol, and octanol, have been investigated by melting-point measurements, differential scanning calorimetry (DSC), rheology, and electron microscopy. The electron microscopic studies revealed that gelation of these solvents occurred through the formation of an entangled network by 1. In all solvents, the gels behave as viscoelastic solids, with G′ . G′′ at frequencies >0.01 Hz (time scales <100 s) and values of G′ up to 500 kPa (50 mM in propanol). The thixotropic character of the gels, however, indicates that the network structure is dynamic at larger time scales. Although the structure of the gels in these solvents is not significantly different, both the thermal stability and the strength of the gels depend on the solvent, and they increase in the order octanol < hexanol < butanol < propanol. It was concluded that solvophobic effects become important for the stabilization of gels of 1 in more polar solvents.