Chemical heterogeneity in interfacial layers of polymer nanocomposites

Abstract

It is well-known that particle-polymer interactions strongly control the adsorption and conformations of adsorbed chains. Interfacial layers around nanoparticles consisting of adsorbed and free matrix chains have been extensively studied to reveal their rheological contribution to the behavior of nanocomposites. This work focuses on how chemical heterogeneity of the interfacial layers around the particles governs the microscopic mechanical properties of polymer nanocomposites. Low glass-transition temperature composites consisting of poly(vinyl acetate) coated silica nanoparticles in poly(ethylene oxide) and poly(methyl acrylate) matrices, and of poly(methyl methacrylate) silica nanoparticles in a poly(methyl acrylate) matrix are examined using rheology and X-ray photon correlation spectroscopy. We demonstrate that miscibility between the adsorbed and matrix chains in the interfacial layers led to the observed unusual reinforcement. We suggest that packing of chains in the interfacial regions may also contribute to the reinforcement in the polymer nanocomposites. These features may be used in designing mechanically adaptive composites operating at varying temperature.

Role of adsorbed chain rigidity in reinforcement of polymer nanocomposites

“…Note that P2VP adsorbed particles in PMA shows no change in modulus after deformation. The higher increment in modulus with PMMA is probably due to the short PMA chains rather than its high rigid nature, leading to a better mixing of chains, a result verified in our previous work . The rigidity of adsorbed chains is thus emphasized with these results as a means of controlling the miscibility and dynamic coupling between adsorbed and matrix chains in interfacial layers.…”

“…Network formation upon heating was observed with the PMMA‐adsorbed particles in PMA matrix with Δ T g of 98 °C. To the contrary, the PVAc–PMA system with a small Δ T g of 25 °C did not behave gel‐like upon heating, but displayed higher reinforcement with the short (40 kg mol −1 ) PMA matrix chains as compared to 140 kg mol −1 PMA . Another blend system with a large Δ T g of 173 °C, PMMA‐poly(ethylene oxide) (PEO), where nanoparticles are adsorbed with PMMA and the matrix polymer is PEO, exhibited a liquid–solid transition at temperatures above the T g 's of both polymers .…”

“…The interfacial effects in composites have been commonly studied for systems where all the chains are chemically identical. The interfacial layers of two miscible polymers of different glass‐transition temperatures ( T g ), otherwise known as dynamically asymmetric polymers, were recently shown to be a promising new method of tuning the elastic moduli responses of nanocomposites to temperature …”

“…Adsorbed polymer chains on nanoparticles dynamically cooperate with matrix polymer in melt state and subsequently control the entanglements and dynamic coupling between chains at interfaces. In our recent work, dynamic asymmetry of miscible blends poly(vinyl acetate) (PVAc)‐poly(methyl acrylate) (PMA) and poly(methyl methacrylate) (PMMA)‐PMA in the presence of particles was shown to control the reinforcement in nanocomposites . Composites of PVAc and PMMA adsorbed particles in PMA matrices were examined to demonstrate the role that T g difference (Δ T g ) between adsorbed and matrix polymers plays on mechanical properties .…”

“…In our recent work, dynamic asymmetry of miscible blends poly(vinyl acetate) (PVAc)‐poly(methyl acrylate) (PMA) and poly(methyl methacrylate) (PMMA)‐PMA in the presence of particles was shown to control the reinforcement in nanocomposites . Composites of PVAc and PMMA adsorbed particles in PMA matrices were examined to demonstrate the role that T g difference (Δ T g ) between adsorbed and matrix polymers plays on mechanical properties . Network formation upon heating was observed with the PMMA‐adsorbed particles in PMA matrix with Δ T g of 98 °C.…”