Multicolor Mechanochromic Epoxy Thermosets That Recognize the Intensity, Type, and Duration of Mechanical Stimulation

• Published in: Macromolecular rapid communications. 2023-03, Vol.44 (6), p.e2200821-n/a
• Main Authors: Lai, Yingsheng, Li, Jiajun, Chen, Mao, Wu, Yeping, Zhang, Yinyu, Zhao, Xiuli, Chen, Zhongtao
• Format: Article
• Language: English
• Subjects: ball mill grinding; Color; epoxies; Epoxy Resins; manual grinding; Mechanical stimuli; mechanochromic polymers; Mortars (comminutors); multicolors; Polymers; Rhodamine; Stimulation; Tensile Strength; Time lag
• ISSN: 1022-1336; 1521-3927
• DOI: 10.1002/marc.202200821

Mechanochromic polymers that exhibit multiple color changes under external mechanical stimulation show great potential for sensor applications. Herein, an epoxy thermoset that can reveal the intensity, type, and duration of mechanical stimulation via a combination of disulfide (DS) and rhodamine (Rh) mechanochromophores is reported. A unique multicolor transition occurs upon ball mill or manual grinding because of the different activation energies of DS and Rh. The epoxy changes color depending on the ball mill grinding duration. Simultaneous activation occurs with a mechanochromic time lag between DS and Rh, and the collision energy strongly affects the relative intensity. A more dramatic multicolor response is observed using a mortar and pestle, as sequential activation occurs upon gentle and strong grinding. Various types of mechanical stimulation can cause different aggregates of the activated Rh moiety and vary the relative mechanosensitivities of Rh and DS, which lead to a different color response. A mechanochromic epoxy that changes multiple colors corresponding to the duration of ball mill grinding and the intensity of manual grinding is reported based on direct combination of two mechanochromophores with distinct activation energies. The types of mechanical stimulation can vary the relative mechanosensitivity of two mechanochromophores, leading to distinct color responses.