Yamamoto Takao, Noguchi Motoki, Maki Yasuyuki, Dobashi Toshiaki
Division of Pure and Applied Science, Graduate School of Science and Technology, Gunma University, Kiryu, Gunma 376-8515, Japan.
Division of Molecular Science, Graduate School of Science and Technology, Gunma University, Kiryu, Gunma 376-8515, Japan.
Gels. 2020 Sep 12;6(3):30. doi: 10.3390/gels6030030.
The volume of a cylindrical polyacrylamide gel was measured when immersed in a binary mixture of isobutyric acid-water at different temperatures and weight fractions of isobutyric acid. Near the upper critical solution temperature of the binary mixture, the curve for gel volume vs. isobutyric acid weight fraction has a shoulder or a peak near the critical weight fraction. On the other hand, in a region away from the critical temperature, the gel volume decreased monotonically with increasing isobutyric acid weight fraction. The cloud point temperature of the binary mixture inside the gel was lower than that outside the gel. Thermodynamic description for the gel in the critical mixture is derived on the basis of the Ising model. By the description, the experimental results are explained consistently. The theoretical analysis shows that the shoulder and the peak appearing in the swelling behavior of the gel are respectively induced by the criticalities of the binary mixture outside and inside the gel. It also shows that the cloud point temperature lowering of the binary mixture inside the gel is attributed to the effective enhancement of the temperature of the binary mixture inside the gel induced by the presence of the gel polymer.
在不同温度以及异丁酸不同重量分数的情况下，测量了圆柱形聚丙烯酰胺凝胶浸入异丁酸 - 水二元混合物时的体积。在二元混合物的上临界溶液温度附近，凝胶体积与异丁酸重量分数的曲线在临界重量分数附近有一个肩部或峰值。另一方面，在远离临界温度的区域，凝胶体积随着异丁酸重量分数的增加而单调下降。凝胶内部二元混合物的浊点温度低于凝胶外部的浊点温度。基于伊辛模型得出了临界混合物中凝胶的热力学描述。通过该描述，实验结果得到了一致的解释。理论分析表明，凝胶溶胀行为中出现的肩部和峰值分别是由凝胶外部和内部二元混合物的临界现象引起的。这也表明，凝胶内部二元混合物的浊点温度降低归因于凝胶聚合物的存在导致凝胶内部二元混合物温度的有效升高。
