engleski

Anomalous diffusion in gelatin gelation

We present a study of the gelation of water solutions of collagen-derived gelatin using pulsed field gradient NMR. For the first time, the complete dynamic structure factor is obtained in dependence on temperature for several gelatin concentrations. This enables us to follow the gelation process with great precision, on length and time scales relevant for self-organization. We found that the material is homogeneous above ~10 􀁐m, with well-defined effective diffusion coefficients mostly following activation temperature dependence. A decrease of those coefficients at the overlap concentration of ~35 g/L [1] is clearly observed, and an anomaly appears close to the solgel transition. At smaller scales anomalous diffusion sets in [2], and power-law tails are observed in the dynamic structure factor. Their nature changes abruptly at the transition. While fractal diffusion seems to provide a good description in the sol state, it is not applicable in gel ; to explain this we suggest that correlated motion plays an important role, in analogy with systems such as glass-forming materials [3] and colloidal gels [4]. It is known that during gelation helical segments form on the polypeptide chains, thus forming interchain bonds [1] ; we discuss the significance of hydrophobic interactions between these segments in mediating correlations at micron scales. This work is enabled by the European Commission through FP7 project #229390 SOLeNeMaR. 1. Guo L., Colby R. H., Lusignan C. P., Howe A., Macromolecules 36, 10009-10020 (2003) 2. Ren S. Z., Shi W., Zhand W. B., Sorensen C. M., Phys. Rev. A 45, 2416 (1992) 3. Parsaeian A., Castillo H. E., Phys. Rev. E 78, 060105 (2008) 4. Duri A., Cipelletti L., Europhys. Lett. 76(5), 972-978 (2006)

gelatin; anomalous diffusion; nuclear magnetic resonance

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