Polymers in 2D confinement: A nanoscale mechanism for thermo‐mechanical reinforcement

Abstract

Acrylate‐clay nanocomposites, a 2D confined system, exhibited unusual increase of thermo‐mechanical properties. The nature of this reinforcement can be ascribed to chain dynamics modification and therefore investigated via dynamic mechanical analysis. Transmission electron microscopy and dynamic light scattering showed a strong nanoconfined regime, 2Rh ≫ d001, whereRhis the polymer's hydrodynamic radius andd001is the clay gallery spacing. The geometrical constraints to polymer dynamics led to significantenhancementof the thermo‐mechanical properties. Adding only 1 wt% nanoclay, the glass transition temperature increased significantly,ΔTg = Tg − Tg,bulk ~ 10°C, and the dynamic modulusE′ increased 10‐fold. Analysis of dynamic mechanical spectra showed an increase of relaxation timeτ, ie, polymer dynamics retardation. Furthermore, the mechanical damping tanδwas strongly attenuated evidencing the reduction of viscous dissipation. The activation energyEaof theα‐transition increased as the confined macromolecules needed to overcome higher energy barriers to achieve configurational rearrangements. The considerable increase of mechanical modulus cannot be explained by polymer composite models, rather it was associated to a “nano‐effect,” scaling with the degree of confinement asE/Ematrix ~ (2Rh/d001)n. This study paves the road for further understanding of polymer dynamics under 2D confinement and the reinforcement mechanism of thermo‐mechanical properties.