Yamamoto Tetsuya, Masubuchi Yuichi, Doi Masao
Department of Materials Physics, Nagoya University, Furocho, Chikusa-ku, Nagoya, 464-8603, Japan.
Center of Soft Matter Physics and its Applications, Beihang University, Xueyuan Road 37, Beijing 100191, China.
ACS Macro Lett. 2017 May 16;6(5):512-514. doi: 10.1021/acsmacrolett.7b00153. Epub 2017 Apr 21.
We use a statistical thermodynamic model to theoretically predict the normal stress of a polymer gel, which is twisted by a rotational rheometer in the parallel plate geometry. This theory predicts that the normal stress of the gel is positive at a short time scale. At longer time, the normal stress decreases significantly due to the redistribution of solvent, but is still positive when the polymer network is in the neo-Hookean regime. The normal stress becomes negative when the polymer network is greatly prestretched in the swelling process because large tension is generated by shearing already prestretched polymers. Our theory predicts the phase diagram with respect to the direction of normal stress as functions of the aspect ratio and swelling ratio of gels. Experimental tests on this prediction may advance our understanding of the physical mechanisms involved in the negative normal stress generated by polymer gels.
我们使用统计热力学模型从理论上预测聚合物凝胶的法向应力，该凝胶由旋转流变仪在平行板几何形状中扭转。该理论预测，在短时间尺度下凝胶的法向应力为正。在较长时间时，由于溶剂的重新分布，法向应力显著降低，但当聚合物网络处于新胡克状态时仍为正。当聚合物网络在溶胀过程中被大幅预拉伸时，法向应力变为负，因为剪切已经预拉伸的聚合物会产生大的张力。我们的理论预测了法向应力方向相对于凝胶的纵横比和溶胀比的相图。对这一预测的实验测试可能会增进我们对聚合物凝胶产生负法向应力所涉及的物理机制的理解。
