Modeling of Intermediate Structures and Chain Conformation in Silica-Latex Nanocomposites Observed by SANS During Annealing

TL;DR

This study investigates how polymer chains and structures evolve during the formation and annealing of silica-latex nanocomposites using contrast-variation small angle neutron scattering, revealing effects of silica content on chain interdiffusion.

Contribution

It provides a quantitative model for the scattering intensity of hairy latex beads and describes the impact of silica content on chain interdiffusion during annealing.

Findings

Low silica content allows full chain dispersion after weeks of annealing.

Higher silica content slows down chain interdiffusion, requiring stronger annealing.

Silica filler does not affect the chain radius of gyration.

Abstract

The evolution of the polymer structure during nanocomposite formation and annealing of silica-latex nanocomposites is studied using contrast-variation small angle neutron scattering. The experimental system is made of silica nanoparticles (Rsi \approx 8 nm) and a mixture of purpose-synthesized hydrogenated and deuterated nanolatex (Rlatex \approx 12.5 nm). The progressive disappearance of the latex beads by chain interdiffusion and release in the nanocomposites is analyzed quantitatively with a model for the scattered intensity of hairy latex beads and an RPA description of the free chains. In silica-free matrices and nanocomposites of low silica content (7%v), the annealing procedure over weeks at up to Tg + 85 K results in a molecular dispersion of chains, the radius of gyration of which is reported. At higher silica content (20%v), chain interdiffusion seems to be slowed down on time-scales of weeks, reaching a molecular dispersion only at the strongest annealing. Chain radii of gyration are found to be unaffected by the presence of the silica filler.