Hybrid Phenol‐Rhodamine Dye Based Mechanochromic Double Network Hydrogels with Tunable Stress Sensitivity

Abstract

Mechanochromic hydrogels, which can switch their color in response to the applied external force, have shown great potential in stress visualization and damage indication. However, the kinds of colors in the reported mechanochromic hydrogels are limited. It is challenging to develop mechanochromic hydrogels with new kinds of color changes. Herein, a kind of mechanochromic double network (DN) hydrogel is reported based on the hybrid phenol-rhodamine mechanophore. The hydrogels turn into orange color with an emission wavelength of around 566/574 nm in response to tensile and compressive stress. The DN hydrogels show great reversibility. The color of DN hydrogels vanishes slowly after releasing the stress. The stress sensitivity can be tailored by the crosslinking density and the mechanophore concentration of the first network. In addition, the influence of the pH on the mechanochromic properties of DN hydrogels is also studied. This study provides an insightful study in tuning the stress sensitivity in the mechanochromic hydrogel, which will be beneficial for the development of mechanochromic materials.

Multi-material 3D Printing of Mechanochromic Double Network Hydrogels for On-Demand Patterning

“…The phenomenon is also found in the previous report. 46 The printed mechanochromic hydrogel structures are also sensitive to the compressive stress (Figure 3d). The printed 3D structures, including seashell, flower, and starfish, are compressed.…”

“…The hydrogel structure printed by microgel ink shows comparable mechanochromic sensitivity with that made from the swelling method. 46 The mechanochromic behaviors of the printed hydrogels are reversible. The fluorescent color of the stretched hydrogel would disappear after being relaxed under the ambient condition for 2 h (Figure S5).…”

“…The mechanochromic behavior of the DNHs is highly dependent on the concentration of the mechanophores. 46 We explore the fabrication of the hydrogel structures which are capable of multi-color change in desired patterns with microgel printing inks containing different mechanophore concentrations. The microgel printing inks are prepared with different concentrations of HPR mechanophores, which are 0, 1, and 2 mol % relative to the concentration of the monomer AMPS in the first network.…”

“…19,20,44,45 However, the mechanochromic hydrogels are usually made as the double network hydrogels (DNHs), which are tough enough to trigger the activation of the mechanophores. 46 The mechanophores are covalently incorporated into the first polymer network of the hydrogels. Then, the first polymer network is further swollen in the polymerizable precursor solution, and the DNHs are obtained after further UV curing.…”

“…For instance, the hydraulic hydrogel robot shows excellent optical and sonic camouflage ability in water . With the covalent incorporation of the mechanophores, hydrogels could be capable of changing color under mechanical force. ,,, However, the mechanochromic hydrogels are usually made as the double network hydrogels (DNHs), which are tough enough to trigger the activation of the mechanophores . The mechanophores are covalently incorporated into the first polymer network of the hydrogels.…”