Strain and stress mapping by mechanochemical activation of spiropyran in poly(methyl methacrylate)

Abstract

The relationship between fracture‐induced mechanophore activation and the strain and stress ahead of a propagating crack in poly(methyl methacrylate) (PMMA) is studied. The mechanophore spiropyran is used as a secondary cross‐linker in rubber toughened PMMA, and the spiropyran‐linked material is subjected to fracture testing. Mechanophore activation is detected and analysed by fluorescence imaging. Digital image correlation is used to measure the strain field ahead of the crack tip, whereas the corresponding stress field is calculated using the Hutchinson–Rice–Rosengren singularity field equations. Mechanophore activation follows a power law dependence on distance from the crack tip and provides both a qualitative and quantitative measure of the strain and stress fields ahead of the crack.

Polymer mechanochemistry-enabled pericyclic reactions

“…The activation is reversible by exposure to ambient light or heat. Since then, SP was used as the most successful mechanophore with regard to publication numbers in a variety of materials to investigate the force-related properties of, e.g., polyacrylates, 7,150,[166][167][168][169][170][171][172][173] polymethacrylates, 174,175,[176][177][178][179][180][181][182][183]184 polyurethanes, 185-193 polydimethylsiloxane (PDMS), [194][195][196][197][198][199][200][201][202] polystyrene, 203 polycaprolacton, 204,205 polyolefins, 206 polycarbonate, 207 polyarylenes 208 and different copolymers. [209][210][211][212][213][214][215][216] Regiochemical effects on mechanochemical SP activation were investigated by varying substitution patterns.…”

Fractography of poly(N-isopropylacrylamide) hydrogel networks crosslinked with mechanofluorophores using confocal laser scanning microscopy

“…However, since the accumulation of non-reversible ruptured bonds is the dominant mechanism leading to failure in polymeric structures, it is important that imminent fracture is reported prior to the formation of any visible macroscopic cracks that will ultimately evolve into the decomposition of the polymer. 7 In recent years, the forceinduced selective scission of covalent and non-covalent bonds was exploited to generate molecules that change their photophysical properties upon the application of mechanical stress and strain, thus allowing the optical detection of material damage. 8,9 While the seminal development of such molecules changing their absorption spectra (mechanochromophores) can be regarded as elegant, their investigation on small scales was hampered intrinsically by the Lambert-Beer law.…”

Multicomponent Stress‐Sensing Composites Fabricated by 3D‐Printing Methodologies

“…Especially the NO 2 ‐functionalized dyes manifest in an intense purple color, finally allowing to quantify the exerted stress within the material. [ 10,27–31 ] Therefore, in view of the multicomponent‐nature of such polymeric materials the use of 3D‐printing methodologies is attractive, allowing to place components for the direct stress‐detection as well as additional reporter molecules required for the quantification of stress into the same material. [ 32,33 ]…”

“…Especially the NO 2functionalized dyes manifest in an intense purple color, finally allowing to quantify the exerted stress within the material. [10,[27][28][29][30][31] Therefore, in view of the multicomponentnature of such polymeric materials the use of 3D-printing methodologies is attractive, allowing to place components for the direct stress-detection as well as additional reporter molecules required for the quantification of stress into the same material. [32,33] A novel and efficient methodology for stress-detection uses mechanophores directly activated by metal/ligand cleavage, coupled to a subsequent catalytic reaction of the then freed metal-coordination-site.…”