Xiong Jun-Ying, Narayanan Janaky, Liu Xiang-Yang, Chong Tan Kok, Chen Shing Bor, Chung Tai-Shung
Department of Chemical and Biomolecular Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Singapore.
J Phys Chem B. 2005 Mar 31;109(12):5638-43. doi: 10.1021/jp044473u.
Kinetics as well as the evolution of the agarose gel topology is discussed, and the agarose gelation mechanism is identified. Aqueous high melting (HM) agarose solution (0.5% w/v) is used as the model system. It is found that the gelation process can be clearly divided into three stages: induction stage, gelation stage, and pseudoequilibrium stage. The induction stage of the gelation mechanism is identified using an advanced rheological expansion system (ARES, Rheometric Scientific). When a quench rate as large as 30 deg C/min is applied, gelation seems to occur through a nucleation and growth mechanism with a well-defined induction time (time required for the formation of the critical nuclei which enable further growth). The relationship between the induction time and the driving force which is determined by the final setting temperature follows the 3D nucleation model. A schematic representation of the three stages of the gelation mechanism is given based on turbidity and rheological measurements. Aggregation of agarose chains is promoted in the polymer-rich phase and this effect is evident from the increasing mass/length ratio of the fiber bundles upon gelation. Continuously increasing pore size during gelation may be attributed to the coagulation of the local polymer-rich phase in order to achieve the global minimum of the free energy of the gelling system. The gel pore size determined using turbidity measurements has been verified by electrophoretic mobility measurements.
讨论了琼脂糖凝胶拓扑结构的动力学及其演变，并确定了琼脂糖凝胶化机制。使用高熔点（HM）琼脂糖水溶液（0.5% w/v）作为模型系统。发现凝胶化过程可明显分为三个阶段：诱导阶段、凝胶化阶段和假平衡阶段。使用先进的流变扩展系统（ARES，Rheometric Scientific）确定凝胶化机制的诱导阶段。当施加高达30℃/分钟的淬火速率时，凝胶化似乎通过成核和生长机制发生，具有明确的诱导时间（形成能够进一步生长的临界核所需的时间）。诱导时间与由最终凝固温度决定的驱动力之间的关系遵循三维成核模型。基于浊度和流变学测量给出了凝胶化机制三个阶段的示意图。琼脂糖链在富含聚合物的相中聚集，这种效应从凝胶化时纤维束质量/长度比的增加中明显可见。凝胶化过程中孔径不断增加可能归因于局部富含聚合物相的凝聚，以实现凝胶系统自由能的全局最小值。通过电泳迁移率测量验证了使用浊度测量确定的凝胶孔径。
