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Author: Stratigaki, Maria ×

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    Multicolor Mechanofluorophores for the Quantitative Detection of Covalent Bond Scission in Polymers
    (Weinheim : Wiley-VCH, 2021) Baumann, Christoph; Stratigaki, Maria; Centeno, Silvia P.; Göstl, Robert
    The fracture of polymer materials is a multiscale process starting with the scission of a single molecular bond advancing to a site of failure within the bulk. Quantifying the bonds broken during this process remains a big challenge yet would help to understand the distribution and dissipation of macroscopic mechanical energy. We here show the design and synthesis of fluorogenic molecular optical force probes (mechanofluorophores) covering the entire visible spectrum in both absorption and emission. Their dual fluorescent character allows to track non-broken and broken bonds in dissolved and bulk polymers by fluorescence spectroscopy and microscopy. Importantly, we develop an approach to determine the absolute number and relative fraction of intact and cleaved bonds with high local resolution. We anticipate that our mechanofluorophores in combination with our quantification methodology will allow to quantitatively describe fracture processes in materials ranging from soft hydrogels to high-performance polymers. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
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    Methods for Exerting and Sensing Force in Polymer Materials Using Mechanophores
    (Weinheim : Wiley-VCH, 2020) Stratigaki, Maria; Göstl, Robert
    In recent years, polymer mechanochemistry has evolved as a methodology to provide insights into the action-reaction relationships of polymers and polymer-based materials and composites in terms of macroscopic force application (stress) and subsequent deformation (strain) through a mechanophore-assisted coupling of mechanical and chemical phenomena. The perplexity of the process, however, from the viewpoint of mechanophore activation via a molecular-scaled disruption of the structure that yields a macroscopically detectable optical signal, renders this otherwise rapidly evolving field challenging. Motivated by this, we highlight here recent advancements of polymer mechanochemistry with particular focus on the establishment of methodologies for the efficient activation and quantification of mechanophores and anticipate to aptly pinpoint unresolved matters and limitations of the respective approaches, thus highlighting possible developments. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
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    Fractography of poly(: N -isopropylacrylamide) hydrogel networks crosslinked with mechanofluorophores using confocal laser scanning microscopy
    (Cambridge : RSC Publ., 2020) Stratigaki, Maria; Baumann, Christoph; van Breemen, Lambert C.A.; Heuts, Johan P.A.; Sijbesma, Rint P.; Göstl, Robert
    Due to their soft and brittle nature, the mechanical characterization of polymer hydrogels is a difficult task employing traditional testing equipment. Here, we endowed poly(N-isopropyl acrylamide) (PNIPAAm) hydrogel networks with Diels-Alder adducts of π-extended anthracenes as mechanofluorophore crosslinkers. After swelling the networks with varying amounts of water and subjecting them to force, we visualized the subsequent fluorescence caused by covalent bond scission with confocal laser scanning microscopy (CLSM) and related the intensities to the macroscopic fracture mechanics and the elastic moduli recorded with traditional uniaxial compression. The sensitivity of the mechanofluorophores allowed the analysis of low levels of mechanical stress produced via a hand-induced needle-puncturing process and, thus, is an alternative to conventional force application methods. The detection and precise localization of covalent bond scission via CLSM helps elucidating the interrelationship between molecular structure and the macroscopic properties of chemically crosslinked polymeric hydrogels. We believe that this micro-scale mechanophore-assisted fractography can establish a new paradigm for the mechanical analysis of soft matter in fields covering traditional polymer and life sciences. © 2019 The Royal Society of Chemistry.