Rubber elasticity is the archetype of the entropic force emerging from the second law of thermodynamics; numerous experimental and theoretical studies on natural and synthetic rubbers have shown that the elasticity originates mostly from entropy change with deformation. Similarly, in polymer gels containing a large amount of solvent, it has also been postulated that the shear modulus (the modulus of rigidity) G , which is a kind of modulus of elasticity, is approximately equivalent to the entropy contribution G S , but this has yet to be verified experimentally. In this study, we measure the temperature dependence of the shear modulus G in a rubberlike (hyperelastic) polymer gel whose polymer volume fraction is at most 0.1. As a result, we find that the energy contribution G E = G ? G S can be a significant negative value, reaching up to double the shear modulus G (i.e., G E ? 2 G ), although the shear modulus of stable materials is generally bound to be positive. We further argue that the energy contribution G E is governed by a vanishing temperature that is a universal function of the normalized polymer concentration, and G E vanishes when the solvent is removed. Our findings highlight the essential difference between rubber elasticity and gel elasticity (which were previously thought to be the same) and push the established field of gel elasticity into a new direction.
展开▼
机译：橡胶弹性是从热力学第二律的熵力的原型;天然和合成橡胶的许多实验和理论研究表明，弹性主要来自熵变形的变形。类似地，在含有大量溶剂的聚合物凝胶中，还已经假定了剪切模量（刚性模量）G，这是一种弹性模量，大致相当于熵贡献GS，但这具有尚未通过实验验证。在该研究中，我们测量剪切模量G在其聚合物体积级分至多0.1的橡皮状（超弹性）聚合物凝胶中的温度依赖性。结果，我们发现能量贡献g e = g？ G S可以是显着的负值，达到剪切模量G（即，Ge≥2g），尽管稳定材料的剪切模量通常是阳性的。我们进一步争辩说，能量贡献G e受到归一化聚合物浓度的通用功能的消失温度，并且在除去溶剂时G e消失。我们的研究结果突出了橡胶弹性和凝胶弹性之间的基本差异（以前认为是相同的），并将建立的凝胶弹性的领域推入新方向。
展开▼
