Abstract
Multi-network elastomers are both stiff and tough by virtue of containing a pre-stretched stiff network that can rupture and dissipate energy under load. However, the rupture of this sacrificial network in all described covalent multi-network elastomers is irreversible. Herein, we describe the first example of multi-network elastomers with a reformable sacrificial network containing mechanochemically sensitive anthracene-dimer cross-links. These cross-links also make our elastomers mechanochromic, with coloration that is both persistent and reversible, because the fluorogenic moiety (anthracene dimer) is regenerated upon irradiation of the material. In proof-of-concept experiments we demonstrate the utility of incorporating anthracene dimers in the backbone of the sacrificial network for monitoring mechanochemical remodeling of multi-network elastomers under cycling mechanical load. Stretching or compressing these elastomers makes them fluorescent and irradiating them eliminates the fluorescence by regenerating anthracene dimers. Reformable mechanochromic cross-links, exemplified by anthracene dimers, hold potential for enabling detailed studies of the molecular origin of the unique mechanical properties of multi-network elastomers.
Highlights
Polymer networks, such as gels and elastomers, are important load-bearing materials thanks to their reversible deformability, which makes them well suited for diverse applications, including in emerging elds of wearable electronics,[1] so robotics,[2] and tissue engineering.[3]
A triple-network (TN) elastomer was prepared from this DN elastomer by repeating the above procedure: in this elastomer, the stiff network accounted for 3.7% of mass
We saw no evidence of anthracene dimer dissociating during photopolymerization, consistent with it being transparent to the wavelengths used to initiate photopolymerization
Summary
Polymer networks, such as gels and elastomers, are important load-bearing materials thanks to their reversible deformability, which makes them well suited for diverse applications, including in emerging elds of wearable electronics,[1] so robotics,[2] and tissue engineering.[3]. The high degree of prestretching of the stiff network means that when it ruptures in a loaded sample, it locally relaxes, making the remaining network less effective at dissipating strain energy.[8] Whether the original mechanical properties of the material can only be restored by regenerating the stiff network to the original degree of prestretching and how to do so, remain to be understood. The dimers are regenerated by irradiating partially degraded materials providing a means of testing how regeneration of dissociated bonds of the sacri cial network affect the mechanical properties of the elastomer
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