Yongqiang Li,Liufang Chen,Chuanfu Li,Lin Lin,Zhibo Yan,Junming Liu
Hydrogels are composed of a three-dimensional network of cross-linked hydrophilic polymer chains and large amounts of water. The physicochemical properties of the polymer-water interface in hydrogels draw our attention. Due to the complex structure of hydrogel systems, it is still a challenge to investigate the interfacial layer properties of hydrogels through experiments. In this work, we investigate the properties of the covalently bonded chitosan-based ice-hydrogels interfacial layer by dielectric relaxation spectroscopy (DRS) techniques in the presence of avoided electrode polarization. The DRS data exhibit that the polymer-water interfacial layer has a strong dielectric signal response, which indicates that a large number of polar electric dipoles or polar molecules may be contained in the interfacial layer. The variable temperature dielectric relaxation behavior of a series of chitosan-base ice-hydrogels showed that the value of dielectric activation energy for different water contents is about 180 kJ/mol, which is much larger than that of the polymer and ice phases, suggesting a strong coupling of polar electric dipoles within the interfacial layer. This work demonstrates the important role of the polymer-water interface in covalently bonded hydrogels, which will provide assistance in the design and application of covalently bonded hydrogels.Keywords:chitosan;ice-hydrogels;dielectric relaxation behavior;activation energy;interface
Yi Zhang,Weiwei Yan,Yanwen Lin,Jiayi Zhu,Haichao Zhao,Tong Li
Materials with low ice adhesion and long-lasting anti-icing properties remain an ongoing challenge in ultralow temperature environments (≤−30 °C). This study presents a gel material consisting of a polymer matrix (copolymer of polyurethane and acrylamide) and an anti-icing agent, ethylene glycol (EG), designed for anti-icing applications at ultralow temperatures. The surface shows a prolonged droplet freezing delay of ca. 322 s at −30 °C and frost resistance properties. It also exhibits an ice adhesion strength of 1.1 kPa at −10 °C and 39.8 kPa at −50 °C, resulting from the interaction between EG and water molecules that hinders the crystallization of ice as well as the significant mismatch between elastic gel and ice. In addition, the gel surface exhibits favorable anti-icing durability, with an ice adhesion strength below 20.0 kPa after 25 icing/deicing cycles and mechanical scratch tests. The gel demonstrates remarkable thermal durability, achieved through the H-bonds between the EG and polymer matrix. The H-bonds further enhance the anti-icing performance, thereby remarkably decreasing EG depletion and improving anti-icing durability. Overall, these properties suggest the potential application of this gel material in harsh environments including polar regions.
Enhancing the low-temperature tolerance of electrochemical energy storage devices (e.g. supercapacitors, rechargeable batteries) in a cold climate is important for automobiles, wearable devices, and smart grids used in high-altitude areas and polar regions. Recently, supercapacitors' longevity and performance under varied temperature conditions, especially low temperature, have received widespread attention. However, until now, the sluggish ion diffusion caused by electrolyte freezing restricts the low-temperature performance and durability of supercapacitors. Herein, an innovative solid-state ion conducting ice gel (IG) with a high conductivity (1.79 × 10−4 S cm−1 at −15 °C), favorable flexibility, and significant low-temperature tolerance was designed and prepared by compositing polyvinyl alcohol (PVA) and CuSO4·5H2O salt through ultra-fast liquid nitrogen freezing. Thereafter, a symmetrical configuration supercapacitor was assembled with two flexible electrodes and IG electrolytes. The IG electrolytes feature a distinct solid-state ion conductor that can provide efficient ion transportability to the supercapacitor at extremely cold temperatures with remarkable electrochemical performances. For example, even at −80 °C, the supercapacitor performed well with a capacitance retention rate of 91.8% after 7000 cycles. Besides, the remarkable mechanical properties derived from the IG electrolytes also endow the supercapacitor with great durability under various harsh deformations in sub-zero surroundings. This work will open up a new avenue for developing versatile solid–gel electrolytes with broad working temperature ranges under harsh conditions for portable and wearable energy storage devices.
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