Confocal Microscopy Visualizes Particle–Crack Interactions in Epoxy Composites with Optical Force Probe-Cross-Linked Rubber Particles

Abstract

Brittle fracture often compromises the durability of glassy polymers. This can be mitigated by reinforcing the matrix with a filler, activating a range of toughening mechanisms. Therefore, it is desirable to better understand the mechanical response of polymer composites, but a direct visualization of the mechanical fate of second-phase inclusions upon material fracture was previously unavailable. Here, rubbery poly­(hexyl acrylate) particles, cross-linked with an optical force probe (OFP), are dispersed within an epoxy matrix, the material is fractured, and particle–crack interactions are visualized with confocal laser scanning microscopy. The dual-fluorescence character of the OFPs allows the differentiation between particles that remain intact and those that are stressed beyond bond scission upon interaction with a propagating crack. The localized activation of OFPs reveals stress gradients within the particles and crack direction pathways, hence providing a new layer of information over fracture events in polymer composites.

Mechanochemical Activation of Red-Light-Excited Triplet–Triplet Annihilation Photon Upconversion

“…The dual-fluorescent BTD-based Diels–Alder adduct OFP is fluorescing sky-blue in the nonactivated state and yellow in the activated state and was synthesized and incorporated into linear PMA chains as reported by us previously, yielding BTD-centered PMA (BTD-PMA). , To achieve TTA UC selectively in the activated OFP form, but not in the nonactivated OFP form, a triplet sensitizer had to be selected (Scheme ). Therefore, we recorded UV–vis absorption spectra of the activated BTD fragment control (Chart ) in both CHCl 3 and toluene (Figure ) at varying concentrations (Supporting Information Figure S1).…”

“…9,10 Here, we report an approach for mechanochemically activated, red-light-excited TTA UC. We make use of our recently reported dual-fluorescent OFPs based on Diels−Alder adducts of 2,1,3-benzothiadiazole (BTD)−anthracene fluorophores with maleimide 27,28 as the mechanochemically latent annihilators and platinum(II) hexylsulfonyl−phthalocyanine PtPc as the triplet sensitizer (Scheme 1). 29 By incorporation of the annihilator motif in the center of linear poly(methyl acrylate) (PMA) chains and subsequent ultrasonication in solution using an immersion probe sonicator at a frequency of 20 kHz, we activate the latent annihilator.…”

Trendbericht: Makromolekulare Chemie 2023

“…68) Göstl und Mitarbeitende machten mechanofluorochrome Vernetzer anwendbar auf die Bruchanalyse von Elastomerpartikel-verstärkten Epoxykompositen. 69) Fery, Besford und Mitarbeitende entwickelten schließlich mechanofluorochrome Polymerbürsten, die den Solvatationsgrad an der Oberfläche ortsaufgelöst anzeigen. 70) W Abb.…”

Fracture Detection in Bio‐Glues with Fluorescent‐Protein‐Based Optical Force Probes

“…[28] The advent of high-resolution microscopy techniques in materials science even enables us to follow macroscopic material damage down to the sub-micrometer scale. [29][30][31][32][33][34][35][36][37] Thereby, OFPs contribute to the development of approaches for materials with improved properties. [38] While OFPs have thus been successfully employed to investigate damage in both synthetic and biomacromolecular materials, the failure of adhesives surprisingly has not yet been examined using OFPs.…”