Supramolecular
plasmonic polymer nanocomposites are versatile soft
materials that hold great promise for many bioapplications as they
combine the functional properties of inorganic nanoparticles with
the dynamic nature of the polymer matrix. Herein, we exploited the
supramolecular chemistry and reducing properties of plant-derived
gallic acid (GA) to drive the in situ formation of gold nanoparticles
(Au NPs) into poly(vinyl alcohol) (PVA)–GA hydrogels. The size
and shape of Au NPs in the plasmonic nanocomposites were tuned from
25 to 221 nm and from anisotropic to spherical, respectively, varying
the Au3+ concentration. From experimental and theoretical
simulation of the extinction spectra, it was possible to assess the
change of the average refractive index of the surrounding Au NPs in
two Au3+ concentration regimes. The changes of the chemical
environment were also tested by Raman and infrared spectroscopy characterization.
Furthermore, the viscoelastic behavior of the supramolecular PVA–GA
hydrogel was also investigated for the plasmonic nanocomposites. At
the highest concentration investigated, the formation of Au NP aggregates
(dimers and trimers) was observed and rationalized with electrodynamic
simulations. Finally, the surface-enhanced Raman spectroscopy properties
were also analyzed using Rhodamine 6G, revealing the extraordinary
capacity of these materials for their application as sensing platforms.
Catechol-containing molecules have been recognized as versatile building blocks for polymer structures with tailormade functional properties. While catechol chemistry via metal− ligand coordination, boronate complexation, and oxidation-driven covalent bonds has been well examined in the past, the hydrogen bonding ability of these intriguing molecules has been dismissed. In this research, we investigated the gelation of poly(vinyl alcohol) (PVA) triggered by the crystallization of a 3,4-dihydroxy-catechol in water. Strong hydrogen bond interactions between PVA and catechol groups afforded supramolecular hydrogels with nearcovalent elastic moduli, yet dynamic, exhibiting reversible gel-tosol phase transitions around 50−60 °C. We studied the impact of the catechol derivative concentration on the gelation kinetics and physicochemical properties of these dynamic materials. Isothermal experiments revealed that heterogeneous crystallization governs the gelation kinetics. Moreover, because of the quasi-permanent cross-links within the supramolecular polymer network, these hydrogels benefit from ultrastretchability (∼600%) and high toughness (900 kJ•m −3 ). Our gelation approach is expected to expand the toolbox of catechol chemistry, opening up new avenues in designing dynamic soft materials with facile control over the phase transition, mechanics, and viscoelastic properties.
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