一种用于可穿戴传感器的超柔性、透明、自粘附、可自愈、抗冻和长期稳定冷冻水凝胶

Ultra-flexible,transparent,adhesive,healable,freezing-tolerant and long-term stable cryogels for wearable sensors

软体器件领域亟需多功能水凝胶,然而,其复杂的功能成分在实际应用中存在安全和环境隐患.在本研究中,单一氯化锂盐在构建冻融聚乙烯醇水凝胶的多层次结构中同时发挥多重作用,激发其前所未有的多功能性和长期稳定性.(1)在冷冻过程中,抗冻盐氯化锂抑制了冰晶的生长,由于冰晶对分子链的排异作用减弱,聚合物分子链靠近程度较弱,实现了分子链网络的非晶化及自由羟基的部分释放.(2)由于氯化锂的水合作用,自由水分子的选择性挥发不仅使高分子网络密集化,同时赋予水凝胶长期稳定性.(3)氯化锂的加入也赋予水凝胶固有特性.因此,最终所得聚乙烯醇水凝胶具备多功能性,包括卓越的柔性(杨氏模量为18.8 kPa)、延展性(704%)、透明度(84%)、粘附性、自愈性、抗冻性(-43℃)和长期稳定性(5个月后宽度和厚度分别为初始尺寸的95%和87%).本研究证明了单一冷冻水凝胶在可穿戴传感器中的应用.考虑到独特的多层次结构及多功能性,预计新一代聚乙烯醇水凝胶将为各种柔性设备提供更多的机会.

Multifunctional hydrogels are highly desirable for soft devices.However,their complex functional constituents pose safe and environmental concerns in the application.Herein,a single salt,LiCl,simultaneously serves as multiple roles in the construction of hierarchical structures for freeze-thawed polyvinyl alcohol(PVA)hydrogels,triggering unprecedented multifunctionality and long-term stability.First,the antifreezing LiCl suppresses the growth of ice crystals and thus creates an unusually weak approach of polymer chains upon freezing due to the weakened expelling of ice,achieving the amorphization of polymer network and releasing some free hydroxyl groups.Second,contributed by bound water with LiCl,the selected evaporation of free water not only densifies polymer networks but also endows the hydrogel with long-term stability.Third,the incorporation of LiCl also adds its intrinsic features to hydrogels.Thus,the ultimate PVA hydrogels exhibit integrated properties of superior flexibility(Young’s modulus of 18.8 kPa),extensibility(704%),transparency(84%),adhesion,self-healing,freezingtolerance(−43℃)and long-term stability(95%width and 87%thickness of the initial size after five months).With these particular hierarchical structures and performances,the capacity of using single cryogels in the wearable sensors is demonstrated.We anticipate that the new generation of PVA hydrogels will provide more opportunities in various soft devices.