Water-borne acrylic polymer/silica nanocomposite coatings
The dynamics and linear viscoelastic response of water-borne acrylic/silica nanocomposite coatings have recently been studied.
In-situ nanostructured latex were prepared using emulsion polymerisation in semi-batch mode and contained up to 3 wt% nanosilica of 7 nm diameter [Romo-Uribe et al., Europ. Polym. J. 2016, 76, 170–186]. High-resolution transmission electron microscopy (HRTEM) of the coatings demonstrated well-dispersed nanoparticles at low silica content. Increasing silica content up to 3 wt% reduced the interparticle distance and evidenced macromolecular confinement. The glass transition temperature Tg increased with silica content, suggesting modification to cooperative dynamics. The macromolecular dynamics was studied by constructing master curves at Tref=Tg + 50 K using time-temperature superposition (TTS).
Viscoelasticresponse exhibits entanglement dilution behaviour
The nanostructured melts were entangled and exhibited only rubber-like and transition regimes. Strikingly, the viscoelastic response exhibited entanglement dilution behavior, i.e. the rubber-like modulus Ge decreased twofold, relative to the neat polymer. Then Ge gradually increased with nanosilica content as the degree of confinement increased. Despite entanglement dilution, the rubber-like regime of the nanocomposites was more elastic than for the neat polymer. The decrease and then increase of entanglement density are nanoconfinement effects as the molecular weight of the polymer matrix and nanocomposites are of the same order of magnitude. The dilated entangled network produced smaller elastic tensile and shear modulus at room temperature.
The study is published in: Progress in Organic Coatings Volume 129, April 2019, Pages 125-132.
