【摘要】 测定了 4个分子量和分子量分布不同、M G不同的海藻酸钠试样在不同浓度下的恒温 (2 5℃ )动态粘弹谱 ,发现 4个试样随溶液浓度升高都会发生溶胶 凝胶 (Sol gel)转变 .实验结果表明 ,该转变符合Winter和Chambon的凝胶化点临界状态的松弛模量G(t)方程 ,由tanδ不依赖于ω的判据求出了海藻酸钠水溶液随浓度变化发生Sol gel转变、出现物理凝胶化的凝胶化点溶液浓度cgel和临界指数n .cgel=7 6wt%～ 8 0wt% ,基本与分子量无关 ;分子量较高的 3个试样的n =0 32～ 0 38,而分子量低的试样的n =0 6 1.该结果表明 ,物理凝胶化主要是由大分子重复单元间的相互作用决定 ,分子链越长则凝胶化点的交联结构越完善更多还原

【Abstract】 The aqueous solutions of 4 sodium alginate samples with different molecular weights,molecular weight distributions and M/G ratios were characterized with GPC,elemental anlaysis,and 1H NMR.The sol gel transition was determined by monitoring the dynamic moduli of these solutions with increasing their concentration within the linear viscoelasticity region at 25℃.This transition was found to obey the Winter and Chambon’s relaxation modulus equation G(t) .From the independency of tan δ on frequency ω ,the concentration of the gel point c gel and the critical exponent for the sol gel transition n were estimated.For all samples c gel is 7 6wt%～8 0wt%,almost independent of molecular weight M w, and n equals 0 32～0 38 for three samples with higher M w and 0 61 for the sample with lower M w.This finding indicates that physical gelation in aqueous solutions of sodium alginate is mainly induced by the interaction between repeat units of the macromolecules,and that the longer chains contribute more perfect crosslinking structure at the gel point.更多还原