We recently found that the energy contribution to the linear elasticity of polymer gels in the as-prepared state can be a significant negative value; the shear modulus is not proportional to the absolute temperature [1]. Our finding challenges the conventional notion that the polymer-gel elasticity is mainly determined by the entropy contribution. Existing molecular models of classical rubber elasticity theories, including the affine, phantom, and junction affine network models, cannot be used to estimate the structural parameters of polymer gels. In this focus review, we summarize the experimental studies on the linear elasticity of polymer gels in the as-prepared state using tetra-arm poly(ethylene glycol) (PEG) hydrogels with a homogenous polymer network. We also provide a unified formula for the linear elasticity of polymer gels with various network topologies and densities. Using the unified formula, we reconcile the past experimental results that seemed to be inconsistent with each other. Finally, we mention that there are still fundamental unresolved problems involving the linear elasticity of polymer gels.

我们最近发现，聚合物凝胶在制备状态下的线性弹性的能量贡献可能是一个显着的负值；剪切模量与绝对温度不成正比 [1]。我们的发现挑战了聚合物凝胶弹性主要由熵贡献决定的传统观念。经典橡胶弹性理论的现有分子模型，包括仿射、幻影和结仿射网络模型，不能用于估计聚合物凝胶的结构参数。在本次重点审查中，我们总结了使用具有均质聚合物网络的四臂聚（乙二醇）（PEG）水凝胶在制备状态下聚合物凝胶的线性弹性的实验研究。我们还提供了具有各种网络拓扑和密度的聚合物凝胶的线性弹性的统一公式。使用统一的公式，我们调和了过去似乎相互不一致的实验结果。最后，我们提到仍然存在涉及聚合物凝胶线性弹性的基本未解决问题。