Interfacial Compatibilization in Ternary Polymer Nanocomposites: Comparing Theory and Experiments

Abstract

In this work, we examine binary and ternary nanocomposites of poly(methyl methacrylate) grafted silica nanoparticles (PMMA-NP), in poly(styrene-ran-acrylonitrile) (SAN), and poly(methyl methacrylate) matrices as a platform to directly probe governing parameters guiding phase behavior and nanoparticle assembly in composite materials. Through the addition of PMMA matrix chains similar in molecular weight to the grafted PMMA chains and significantly smaller than the SAN matrix chains, we observe increased nanoparticle miscibility in off-critical compositions due to interfacial segregation of PMMA matrix chains. A simple interfacial model provides a general guideline for predicting the extent of compatibilization. Further insights on compatibilization behavior are provided by polymer particle pair correlation functions and structure factors obtained using Polymer Reference Interaction Site Model theory calculations as well as polymer concentration profiles from molecular dynamics simulations. This study serves as a guideline to facilitate PNC processing and design of materials for a broad range of technological applications.

Grafted Nanoparticle Surface Wetting during Phase Separation in Polymer Nanocomposite Films

“…We attribute this increased miscibility window to a decrease in the PMMA molecular weight, namely, decreasing from 91 to 19 kg/mol. An analysis of this behavior was described along with a comparison with the PRISM theory in the work by Maguire et al Overall, this result indicates that dense polymer brushes grafted to NPs (0.7 chains/nm 2 ) exhibit enthalpic interactions comparable to their analogues in a polymer blend.…”

“…The bulk phase diagrams of a PMMA (91 kg/mol)/SAN (118 kg/mol) blend and of a PMMA (19 kg/mol)-NP/SAN (118 kg/mol) PNC have been previously constructed using complementary techniques of cloud point, TEM, and small-angle X-ray scattering. , Figure a depicts the phase diagram of the polymer blend, PMMA/SAN, which exhibits a lower critical solution temperature (LCST) of 160 °C . The phase diagram of the PNC, PMMA-NP/SAN, is plotted as a function of PMMA-NP weight fraction in Figure b . Comparing Figures a,b shows that the phase boundaries for the PNC and the binary polymer blends are similar near the critical point with a shift toward lower PMMA (PMMA-NP) weight fractions.…”

Direct Structural Evidence for Interfacial Gradients in Asymmetric Polymer Nanocomposite Blends

“…On the other hand, the effect of the introduction of NPs on the phase behavior is weak and systemdependent as shown by a few phenomenological theories [26][27][28][29] and measurements. [30][31][32] Ginzburg 26 predicted the effect of nanoparticles on the phase separation of PNC blends. He showed in particular that a possible enthalpic compatibilizing effect of NPs is counterbalanced for larger particles (RNP > Rg of the chain) by the entropic penalty on the chain conformation.…”

“…The temperature dependence of decomposition has also been studied by SANS and isotopic labeling, allowing comparison to the Ginzburg–Landau approach of phase transitions and identifying the limits of mean-field theories. , The phase diagrams of pure blends are thus relatively well described by mean-field theories of known limitations. On the other hand, the effect of the introduction of NPs on the phase behavior is weak and system-dependent, as shown by a few phenomenological theories − and measurements. − Ginzburg predicted the effect of NPs on the phase separation of PNC blends. He showed in particular that a possible enthalpic compatibilizing effect of NPs is counterbalanced for larger particles ( R NP > R g of the chain) by the entropic penalty on the chain conformation.…”

Understanding the Effect of Heterogeneous Particle Functionalization on Graft–Matrix Wetting and Structure in Polymer Nanocomposites Containing Grafted Nanoparticles Using Multiscale Modeling and Simulation

“…In a related system of polymer nanocomposites (PNCs) composed of a matrix polymer and added nanoparticles with grafted polymer chains, several theory and simulation studies have shown that by tuning the PNC design (shape and size of particles, grafting density, polydispersity) and/or graft–matrix chemistry, the underlying entropic and enthalpic driving forces can be tailored to favor particle dispersion in the matrix. − In particular, these studies show that at high grafting densities, tuning the extent of interpenetration between graft and matrix chains (i.e., grafted layer wetting) is key to controlling the dispersion or aggregation of particles in the matrix. For PNCs with chemically similar graft and matrix chains, in the high-grafting-density regime, morphology is driven purely by entropic driving forces and the grafted layer wetting can be increased by choosing the matrix polymer chain length to be smaller than the graft polymer chain length, − increasing the stiffness of graft and matrix chains, , reducing particle diameter relative to graft polymer chain size, − or choosing graft polymers with dispersity in molecular weight. − ,, On the other hand, in PNCs with chemically dissimilar graft and matrix chains, the enthalpic driving forces arising due to direct graft–matrix interactions can either cooperate or compete with entropic driving forces, causing the grafted layer wetting to also depend on the choice of graft and matrix chemistries. ,− These competing entropic and enthalpic driving forces for graft–matrix wetting/dewetting and particle dispersion/aggregation are also relevant for dense polymer solutions and formulations with functionalized particles.…”