Interplay of Phase Separation and Thermoreversible Gelation in Aqueous Methylcellulose Solutions
Interplay of Phase Separation and Thermoreversible Gelation in Aqueous Methylcellulose Solutions
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DOI：
10.1021/ma3019359
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发表时间：
2013-01-08
期刊：
影响因子：
5.5
通讯作者：
Brackhagen, Meinolf
中科院分区：
文献类型：
--
作者：
Arvidson, S. A.;Lott, J. R.;Brackhagen, Meinolf
在相似的热历史下进行流变学和浊度测量，以探测一组三种甲基纤维素（MC）材料在冷水中水合后具有相似的取代度（DS）和对比的分子量的热可逆凝胶化和相分离之间的关系。使用频率无关的损失正切来鉴定MC溶液中的凝胶点（T-凝胶），其完全超过链重叠浓度（c >= 10 c *）。633 nm激光透过溶液的透射率表明，所有MC溶液在胶凝后均会发生混浊，相对透射率为86%，与胶凝点密切相关。发现MC溶液的凝胶化温度随着MC浓度的增加而降低，并且所有分子量的结果叠加。使用凝胶和浊点，相图的构建，揭示了明确的MC解决方案直接转变成混浊的凝胶。完全开发的MC凝胶的频率无关的存储模量与phi（2.3）成比例，与纠缠系统的理论和实验一致。MC的凝胶化对升温速率有很强的依赖性，而凝胶的熔融对降温速率的依赖性很小，表明MC的热凝胶化是通过成核和生长机制进行的，而不是Spinodal分解。
Rheology and turbidity measurements were performed under similar thermal histories to probe the relationship between thermoreversible gelation and phase separation for a set of three methylcellulose (MC) materials with similar degrees of substitution (DS) and contrasting molecular weights after hydration in cold water. Frequency-independent loss tangents were used to identify the gel point (T-gel) in MC solutions well over the chain overlap concentration (c >= 10c*). Transmittance of 633 nm laser light through the solutions revealed that all MC solutions cloud upon gelling, with a relative transmittance of 86% closely associated with the gel point. The gelation temperature of MC solutions was found to decrease with increasing MC concentration and the results for all molecular weights superposed. Using gel and cloud points, a phase diagram was constructed which reveals that clear MC solutions transition directly into turbid gels. Frequency-independent storage moduli of fully developed MC gels scaled with phi(2.3), consistent with theory and experiment of entangled systems. Gelation of MC has strong dependence on heating rate while the melting of the gel has little dependence on cooling rate, suggesting that thermogelation of MC proceeded by a nucleation and growth mechanism rather than spinodal decomposition.