Tsukeshiba Hiroyuki, Huang Mei, Na Yang-Ho, Kurokawa Takayuki, Kuwabara Rikimaru, Tanaka Yoshimi, Furukawa Hidemitsu, Osada Yoshihito, Gong Jian Ping
Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan.
J Phys Chem B. 2005 Sep 1;109(34):16304-9. doi: 10.1021/jp052419n.
The mechanical strength of double network (DN) gels consisting of highly cross-linked poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) as the first component and linear polyacrylamide (PAAm) as the second component has been investigated by varying the molecular weight of the second polymer PAAm, M(w). The experimental results reveal that, for toughening of the DN gels, (1) M(w) is one of the dominant parameters; (2) there is a critical value of M(w) = 10(6) for a remarkable enhancement; (3) the fracture energy of DN gels with a M(w) larger than 10(6) reaches a value as high as 10(3) J/m(2). By plotting the strength of DN gels (fracture stress sigma and fracture energy G) against a characteristic parameter of c[eta], where c is the average concentration of PAAm in the DN gels and [eta] is the intrinsic viscosity of PAAm, it is found that the dramatic increase in the mechanical strength of the DN gels occurs above the region where linear PAAm chains are entangled with each other. Thus, we conclude that the entanglement between the second component PAAm plays an important role of the toughening mechanism of DN gels. This result supports the heterogeneous model, which predicts the presence of "voids" of the first network PAMPS with a size much larger than the radius of the second polymer PAAm.
研究了由高度交联的聚（2-丙烯酰胺-2-甲基丙烷磺酸）（PAMPS）作为第一组分和线性聚丙烯酰胺（PAAm）作为第二组分组成的双网络（DN）凝胶的机械强度，通过改变第二聚合物PAAm的分子量M(w)来进行研究。实验结果表明，对于DN凝胶的增韧，（1）M(w)是主要参数之一；（2）存在一个临界值M(w)=10^6，可实现显著增强；（3）M(w)大于10^6的DN凝胶的断裂能高达10^3 J/m²。通过绘制DN凝胶的强度（断裂应力σ和断裂能G）与c[η]的特征参数的关系图，其中c是DN凝胶中PAAm的平均浓度，[η]是PAAm的特性粘度，发现DN凝胶机械强度的显著增加发生在线性PAAm链相互缠结的区域之上。因此，我们得出结论，第二组分PAAm之间的缠结对DN凝胶的增韧机制起着重要作用。这一结果支持了非均相模型，该模型预测第一网络PAMPS中存在尺寸远大于第二聚合物PAAm半径的“空隙”。
