Modification of Hydrophobic Hydrogels into a Strongly Adhesive and Tough Hydrogel by Electrostatic Interaction

Synthetic hydrogels with hydrophobic interactions, which show excellent mechanical performance and good anti-swelling ability in saltwater, have great potential in various industries, such as soft robots, 3D printing, and wearable sensors. Normally, hydrophobic molecules inside a hydrophobic hydrogel tend to aggregate to form a large hydrophobic domain, leading to a phase separation phenomenon because water is a poor solvent of the hydrophobic domain. This aggregation, however, inhibits the adhesion of the hydrophobic hydrogel to various dry materials and thus limits its application in device and sensor industries. In this study, we report the synthesis of hybrid hydrogels with ionically and hydrophobically cross-linked networks. This novel hybrid hydrogel can strongly adhere to various substrates, such as glass, polypropylene, silicone, wood, and polytetrafluoroethylene, with a maximum adhesion strength measured to be 100 kPa. Meanwhile, this hybrid hydrogel can be stretched beyond 8-10 times of its initial length. We attribute this observed strong adhesion and high toughness properties to the synergy of electrostatic interactions and hydrophobic associations. With the strong adhesion and excellent tensile performance, these hydrogels may serve as a model system to explore the strong adhesion mechanism of hydrophobic hydrogels and expand the scope of hydrogel applications.

具有疏水相互作用的合成水凝胶在盐水环境中表现出优异的力学性能和良好的抗溶胀能力，在软体机器人、3D打印和可穿戴传感器等多个行业具有巨大潜力。通常，疏水水凝胶内部的疏水分子倾向于聚集形成大的疏水区域，由于水是疏水区域的不良溶剂，会导致相分离现象。然而，这种聚集会抑制疏水水凝胶与各种干燥材料的粘附，从而限制了其在器件和传感器行业的应用。在本研究中，我们报道了具有离子交联和疏水交联网络的杂化水凝胶的合成。这种新型杂化水凝胶能够牢固地粘附在各种基底上，如玻璃、聚丙烯、硅橡胶、木材和聚四氟乙烯，测得的最大粘附强度为100千帕。同时，这种杂化水凝胶可拉伸至其初始长度的8 - 10倍以上。我们将这种观察到的强粘附和高韧性特性归因于静电相互作用和疏水缔合的协同作用。凭借强粘附性和优异的拉伸性能，这些水凝胶可作为一个模型系统，用于探索疏水水凝胶的强粘附机制并扩大水凝胶的应用范围。