Rheological monitoring of polyacrylamide gelation: Importance of cross-link density and temperature
Rheological monitoring of polyacrylamide gelation: Importance of cross-link density and temperature
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DOI：
10.1021/ma049072r
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发表时间：
2004-10-05
期刊：
影响因子：
5.5
通讯作者：
Giasson, S
中科院分区：
文献类型：
--
作者：
Calvet, D;Wong, JY;Giasson, S
小应变下的动态剪切振荡测量用于表征原位聚合过程和交联聚丙烯酰胺水凝胶的粘弹性。水凝胶是通过丙烯酰胺（8 wt%）在不同温度下、不同浓度的交联剂 N,N'-亚甲基双（丙烯酰胺）（BIS）的自由基氧化还原聚合来合成的。弹性模量 G' 和粘性模量 G" 都是在平行流变仪板之间直接发生的凝胶化过程中实时测量的。弹性模量 G' 随频率保持恒定，G'(omega) 近似于 cte，并且明显大于 G"(omega)，这是发达的交联聚合物网络的特征。弹性模量的温度扫描显示G'(T)与取决于聚合温度T-pol的比例值呈线性关系。这一观察结果与经典的类橡胶弹性理论一致，即 G' = n(e)RT，其中 n(e) 是活跃网络链接密度。结果证实，最终的 G' 和 G" 对交联剂浓度和聚合温度敏感。此外，G' 在大范围的 BIS 浓度范围内遵循线性级数。对于给定的丙烯酰胺单体浓度，存在最佳双（丙烯酰胺）交联剂浓度和最佳聚合温度，从而产生“理想”水凝胶，即表现出最大弹性。
Dynamic shear oscillation measurements at small strains are used to characterize the polymerization process in situ and the viscoelastic properties of cross-linked polyacrylamide hydrogels. Hydrogels are synthesized by free-radical redox polymerization of acrylamide (8 wt %) for different concentrations of cross-linker, N,N'-methylenebis(acrylamide) (BIS), at different temperatures. Both elastic modulus G' and viscous modulus G" are measured in real time during the gelation which takes place directly between parallel rheometer plates. The elastic modulus G' remains constant with frequency, G'(omega) approximate to cte, and is significantly larger than G"(omega), characteristic of a well-developed cross-linked polymer network. Temperature scanning of the elastic modulus shows that G'(T) is a linear relationship with a proportionality value that depends on the polymerization temperature T-pol. This observation is in agreement with the classical theory of rubberlike elasticity, i.e., G' = n(e)RT where n(e) is the active network links density. The results confirm that the final G' and G" are sensitive to the cross-linker concentration as well as the polymerization temperature. Moreover, G' follows a linear progression over a large range of BIS concentration. For a given acrylamide monomer concentration, there exists an optimal bis(acrylamide) cross-linker concentration and an optimal polymerization temperature which give rise to an "ideal" hydrogel, i.e., exhibiting a maximal elasticity.