Gels are composed of crosslinked polymer networks and solvent molecules imbibed into the networks. Gels are both ubiquitous in nature and important engineering materials widely used in many applications. Due to their biocompatibility, stimuli-responsiveness, and compliance, gels gain an edge over traditional materials, such as metals and composites in many modern engineering applications. In the past, the static and kinetic properties of gels have been widely studied. However, the dynamic properties of gels, particularly their structural damping, remain largely unknown even though gels are often under dynamic conditions in various applications. The literature of soft materials is lacking both damping data for hydrogels and a standard testing method to that end. This work reports experimentally identified structural damping data for a set of hydrogel samples via resonant vibration tests for the first bending mode. Beam-shaped samples of rectangular cross-section are clamped vertically at both ends and tested under linear base excitation. An analysis of the frequency response functions based on the Euler–Bernoulli beam theory is conducted to extract Young’s modulus and structural damping values. In the experiments, polyacrylamide gels of three different compositions and polydimethylsiloxane (PDMS) elastomers of two different compositions are prepared and tested. The remarkable result is that the hydrogels have 80% less damping than PDMS, even though hydrogels are an order of magnitude softer than PDMS. The molecular origins of the damping in hydrogels and PDMS are discussed. The low damping of gels may open new avenues of research and applications of soft materials in structural dynamics and wave propagation, such as metamaterials and topological insulators, among others.

凝胶由交联的聚合物网络和吸收到网络中的溶剂分子组成。凝胶本质上无处不在，并且是在许多应用中广泛使用的重要工程材料。由于其生物相容性，刺激响应性和顺应性，在许多现代工程应用中，凝胶相对于传统材料（例如金属和复合材料）具有优势。过去，已经对凝胶的静态和动力学性质进行了广泛的研究。然而，即使凝胶在各种应用中经常处于动态条件下，其动态性质，特别是其结构阻尼，仍是很大程度上未知的。软质材料的文献既缺乏水凝胶的阻尼数据，也缺乏为此目的提供标准测试方法。这项工作通过第一弯曲模式的共振振动测试报告了一组水凝胶样品的实验确定的结构阻尼数据。将矩形横截面的束状样品两端垂直夹住，并在线性基础激励下进行测试。对基于欧拉-伯努利梁理论的频率响应函数进行了分析，以提取杨氏模量和结构阻尼值。在实验中，制备并测试了三种不同成分的聚丙烯酰胺凝胶和两种不同成分的聚二甲基硅氧烷（PDMS）弹性体。引人注目的结果是，即使水凝胶比PDMS柔软一个数量级，其水凝胶的阻尼也比PDMS小80％。讨论了水凝胶和PDMS中阻尼的分子起源。