Rheological Properties and Scaling Laws of 魏-Carrageenan in Aqueous Solution

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• 作者：Sijun Liu ; Wai Luen Chan ; Lin Li
• 刊名：Macromolecules
• 出版年：2015
• 出版时间：October 27, 2015
• 年：2015
• 卷：48
• 期：20
• 页码：7649-7657
• 全文大小：656K
• ISSN：1520-5835

文摘

Rheological properties, gel network structures, and scaling laws for 魏-carrageenan in aqueous solution were studied by rheology and field emission scanning electron microscopy (FESEM). The FESEM micrographs verified that the 魏-carrageenan gels were formed by the formation of fibrils. The critical gel concentration, c_g, obtained using the Winter鈥揅hambon criterion, was found to be proportional to temperature as expressed by c_g 鈭?T^0.85 where T is the temperature in 掳C. At the gel point, the critical relaxation exponent n obtained was a constant (n = 0.62) and independent of temperature. The critical gel strength S_g increased with increasing c_g. A constant gel strength S_g/c_g was obtained by normalizing S_g with c_g to eliminate the effect of temperature, showing a unique character of 魏-carrageenan in aqueous solution during gelation. The molecular structure of the junctions at the gel point was analyzed using the modified Eldridge鈥揊erry model, which supported the similarity of the fractal structure in the 魏-carrageenan gels. Before the gel point, the zero shear viscosity 畏₀ of 魏-carrageenan solutions diverged as the gelling system approached to the gel point, and a scaling law, 畏₀ 鈭?蔚^{鈥撐?/sup>, was established, where 蔚 is the relative distance of 魏-carrageenan concentration c from c_g and 纬 is the scaling exponent that was found to be 1.6. Beyond the gel point, the plateau modulus G_e of 魏-carrageenan gels depended on the polymer concentration according to a power law, G_e 鈭?蔚z, where z was found to be 2.7. The critical gel exponent n evaluated from 纬 and z agreed well with the value of n determined from the Winter鈥揅hambon criterion, further indicating that the characteristic relaxation time of the pregel and the postgel follows the same power law (symmetry at c = c_g) for 魏-carrageenan in aqueous solution.}