Montmorillonite nanoclay aggregated in a fractal structure in an acrylic-styrene matrix, slowed the chain dynamics and increased an order of magnitude the tensile modulus

Homogenously dispersed montmorillonite (MMT) nanoclay in an acrylic-styrene copolymer formed fractal structure in the solid state and induced an order of magnitude increase of tensile modulus. The glass transition temperature, T-g, the thermal decomposition temperature, T-dec, and the water contact angle also increased with MMT content. The copolymer was based on 60% butyl acrylate (BA), 38% styrene (sty), and 2% methacrylic acid (MAA), and MMT was incorporated in-situ up to 25 wt% content. Cast films were optically transparent, and transmission electron microscopy (TEM) showed that MMT was well dispersed throughout the acrylic matrix. Wide-angle X-ray scattering revealed that MMT was exfoliated up to 5 wt% content, and at higher MMT content, the chains intercalated the galleries. Small-angle X-ray scattering (SAXS) showed that MMT aggregated into fractal objects of dimension 2 (i.e., I similar to vertical bar q vertical bar(-2)), consistent with scattering from randomly distributed platelets. Nuclear magnetic resonance (NMR) demonstrated slower chain dynamics in the presence of MMT in the fluid (T2 measurements) and solid (magic angle spinning) states. Dynamic mechanical analysis demonstrated the reduction of damping tan delta and increase of segmental relaxation time tau(e). Therefore, the polymer-nanoclay interaction and the chain nanoconfinement imposed by nanoclay promoted slower chain dynamics and the increase of thermal properties and mechanical modulus, thus enabling polymer nanocomposites with enhanced physical properties.

Automated summary

The study revealed that homogenously dispersed montmorillonite nanoclay in an acrylic-styrene copolymer formed a fractal structure in the solid state, significantly increasing tensile modulus. With an increase in nanoclay content, the glass transition temperature, thermal decomposition temperature, and water contact angle also increased.