Particle dispersion governs nano to bulk dynamics for tailored nanocomposite design

Nanoparticle addition can expand bioplastic use, as the resultant nanocomposite features e.g., improved mechanical properties.

It is generally hypothesised that the nanoparticle-polymer interaction strength is pivotal to reduce polymer dynamics within the interphasial region and beyond.

Translating nanoscale phenomena to bulk properties is challenging, as traditional techniques that probe interphasial dynamics are limited to well-dispersed systems. Laser speckle imaging (LSI) enabled us to probe interphasial nanoscale dynamics of samples containing aggregated nanoparticles. We relate these LSI-derived relaxation times to bulk rheological properties at a micro scale.

Nanocomposites with well-dispersed PDMS-coated titanium dioxide nanoparticles of ∼100 nm showed higher viscosities than nanocomposites containing aggregated PVP- and PAA-coated nanoparticles of 200-2000 nm. Within the interphasial region, nanoparticle addition increased relaxation times by a factor 10¹-10², reaching ultraslow relaxations of ∼10³ s. While the viscosity increased upon nanoparticle loading, interphasial relaxation times plateaued at 5 wt% for nanocomposites containing well-dispersed nanoparticles and 10 wt% for nanocomposites containing aggregated nanoparticles. Likely, interphasial regions between nanoparticles interact, which is more prominent in systems with well-dispersed nanoparticles and at higher loadings. Our results highlight that, contrary to general belief, nanoparticle dispersion seems of greater importance for mechanical reinforcement than the interaction between polymer and particle.