Entanglement density and particle dynamics in rigid interfacial layers of polymer nanocomposites

Abstract

Intermixing between chemically different polymers around nanoparticles creates chemically heterogeneous layers, exhibiting unusual dynamic anomalies due to dynamic confinement and coupling phenomena in polymer nanocomposites. Interfacial mixing of chains is possible when adsorbed chains are mobile above their glass-transition temperature, leading to enhanced entanglement density at the interphase. Linear rheology data of polymer nanocomposites with chemically heterogeneous interphases around nanoparticles were analyzed over a wide frequency range to investigate the role of chain rigidity on matrix chain relaxations and particle diffusion. Our findings show that nanoparticles adsorbed with less rigid polymer move in a sub-diffusive mode. Nanoparticles adsorbed by flexible polymers can slow down the matrix polymer dynamics and particle diffusion, and this interphase effect enhances the viscoelastic properties of the whole polymer nanocomposite.

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

“…In previous studies, we studied the role of chain rigidity on the reinforcement of PEO and poly(methyl acrylate) (PMA) nanocomposites. 20,27,39 We showed that particles adsorbed with less rigid polymers improved the entanglement density of PMA matrix chains. 20 Consequently, the dense interphase layer slowed down the matrix polymer dynamics and the particle diffusion.…”

“…Interfacial chain mobility gradient, chain relaxations, and particle dynamics have been extensively explored to understand the dynamic response of polymer nanocomposites. 9−17 The viscoelastic properties of composites consisting of one homopolymer type are governed by chain conformations, 18,19 adsorption, 18,20,21 and confinement of chains 22−25 in the vicinity of nanoparticles.…”

“…32−37 This complex dynamic heterogeneity governs the linear viscoelastic behavior of polymer nanocomposites. Several factors such as chain length, 21 rigidity, 18,20,38 chain architecture, 18 and glass transition temperature differences 21 control the mixing as well as the packing and entanglement density of chains within the interfacial layers. In previous studies, we studied the role of chain rigidity on the reinforcement of PEO and poly(methyl acrylate) (PMA) nanocomposites.…”

“…20,27,39 We showed that particles adsorbed with less rigid polymers improved the entanglement density of PMA matrix chains. 20 Consequently, the dense interphase layer slowed down the matrix polymer dynamics and the particle diffusion. 20 This interphase layer has been investigated for two different composite systems, where grafted and matrix chains were chemically identical and different.…”

“…20 Consequently, the dense interphase layer slowed down the matrix polymer dynamics and the particle diffusion. 20 This interphase layer has been investigated for two different composite systems, where grafted and matrix chains were chemically identical and different. 18,40 In the chemically identical system, large-amplitude oscillatory shear was applied to enhance the mixing of matrix chains into the grafts and to orient the particles in the direction of shear flow.…”