Abstract:

Hydrogels, composed of crosslinked macromolecules and water, can be formed by chemical or physical interactions and can absorb many times as much water as they contain. The soft and moist properties of the hydrogel are similar to those of biological tissue, and it can respond to a wide range of external stimuli. Due to its extremely high water content and good biocompatibility, the hydrogel has shown broad application prospects in sensors, soft robots, flexible electronics, drug delivery and tissue engineering. Photochromic materials, which can undergo significant and reversible color changes under certain light conditions, have attracted many important studies in the fields of storage, anticounterfeiting, display, and optical switching. Currently, the structurefunction relationship among various photochromic hydrogels has gained a lot of attention. It is still challenging to study the combination of traditional photochromic materials with hydrogels. At the same time, the high cost and complex preparation technology of some photochromic materials are also urgent problems to be solved in the future development of related functional materials. The preparation method of photochromic soft materials with low cost, simple process and good chemical stability is sought to provide new design ideas for a new generation of flexible and intelligent colorchanging materials.

In order to prepare highstrength hydrogels with photochromic properties, acrylamide (AAM) was used as the main monomer of the networks, and dodecyl dimethyl betaine (BS12) was used as a surfactant. The mechanical properties of photochromic hydrogels were enhanced by chemical crosslinking and hydrophobic association through the combination of BS12 rich in positive charges and photochromic ammonium molybdate ［(NH4)6Mo7O24 ·4H2O］. The micelles were analyzed by transmission electron microscopy (TEM) and dynamic light scattering (DLS) laser particle size analyzer, and the absorbance, transparency, and mechanical properties of photochromic hydrogels were measured by UVvis and universal testing machine. The results showed that the hydrogel exhibits high transparency and can change color under the irradiation of UV light for only two min, and the fading process can be easily achieved in the air environment. The tensile strength of hydrogels can reach 215 kPa and the fracture elongation can reach 1480%. After five stretching cycles, the lost energy is reduced by about 46%, and the dissipation energy remains unchanged.

The photochromic hydrogel is envisioned as potentially being applied as flexible and stretchable devices for visual display and storage. The photochromic hydrogel has the potential to be a choice for wearable flexible devices, artificial intelligence systems, and erasable optical displays. It might be thought of as a promising candidate for wearable flexible devices, artificial intelligence systems, and erasable optical displays. Therefore, the strategy for designing a soft photochromic material would open the next generation of flexible and stretchable devices.

Key words: hydrogel, photochromic, dodecyl dimethyl betaine, ammonium molybdate tetrahydrate, acrylamide, hydrophobic association, photochromic hydrogels

摘要： 为制备具有高强度光致变色水凝胶材料，以丙烯酰胺(AAM)作为网络主单体，十二烷基二甲基甜菜碱(BS12)为表面活性剂，通过富含正电荷的BS 12与光致变色钼酸铵［(NH4)6Mo 7O2·4H2O］静电作用相结合，采用化学交联和疏水缔合共同作用增强光致变色水凝胶力学性能。通过透射电子显微镜(TEM)与动态光散射粒度分析仪(DLS)分析了胶束的微观形貌，采用紫外可见吸收光谱仪(UV Vis)、万能试验机分别测量了光致变色水凝胶的吸光度、透明度和机械性能。结果表明：该凝胶材料表现出高透明性且在UV照射下仅需2 min出现颜色转变，在空气环境中很容易恢复到无色状态；其抗拉强度达到215 kPa，断裂伸长率可达1480%左右；且经过5次拉伸循环后，损耗能降低了约为46%，耗散能基本保持不变。

关键词: 十二烷基二甲基甜菜碱(BS 12), 钼酸铵, 丙烯酰胺, 疏水缔合, 光致变色水凝胶