Thermally Activated Shear Stiffening in Polymer-Grafted Nanoparticle Composites for High-Temperature Adhesives

Abstract

Thermally activated shear stiffening viscoelastic fluid can help to improve the performance of viscoelastic dampers and high-temperature adhesives. Polymer nanocomposites with heterogeneous interphases are applied to design such adaptive materials. In this work, shear stiffening in polymer-grafted nanoparticle composites is investigated. We report the linear rheological responses of grafted particle composites before and after large-amplitude oscillatory shear application. We found that interfacial mixing of short grafts with chemically different long matrix chains led to the enhancement of plateau moduli and terminal relaxations, unlike with the long grafts. Moreover, we showed that the elastic modulus of grafted chains was enhanced upon deformation through inter-diffusion and entanglements of interfacial layers with the short matrix chains in both grafted systems. These results suggest that dynamic coupling between chemically different polymers away from nanoparticle surfaces is a design strategy to achieve the thermally stiffening behavior in polymer nanocomposites.

The effect of dynamically heterogeneous interphases on the particle dynamics of polymer nanocomposites

“…It is worth mentioning that rheological properties of the grafted composites were tested and reported in our previous work. 41 We found that short matrix chains dynamically coupled better with the long-grafted chains and reinforced the system at high temperatures. Here, we will present the relaxations of PMMA-grafted Fe 3 O 4 (15 nm) nanoparticles in 20 kDa and 160 kDa PMA matrices.…”

“…This dense layer effect was verified by the higher reinforcement observed with the short (20 kDa) PMA chains in our previous work. 41…”

“…Adsorption of polymers onto nanoparticles and preparation of polymer-grafted Fe 3 O 4 nanoparticles were reported in previous works. 23,41 Here, we will describe the preparation of polymer adsorbed SiO 2 nanoparticles. SiO 2 in butanone with 15 nm diameter was purchased from Nissan Chemical Corporation.…”

“…The dynamic coupling between the two polymers with different glass-transition temperatures (T g 's) was found to strengthen the composite as a result of slowed chain dynamics when all chains were mobile at high temperatures. 40,41 The matrix chain length and the adsorbed chain rigidity were found to affect this dynamic coupling process. 22,23,42 Local viscosities measured by magnetic heating of iron oxide nanoparticles were directly influenced by the rigidity of adsorbed polymers and chemical heterogeneities of their interfacial layers.…”

Recent scattering approaches to structure and dynamics of polymer nanocomposites

“…Thermally activated shear stiffening for the grafted chain in a polymer matrix was observed by Wu et al (2022). The thermal stiffening effect can be used in devices that require high modulus and high viscosity under the oscillating shear application.…”