Nonlinear Architectures Can Alter the Dynamics of Polymer–Nanoparticle Composites

Abstract

Polymer nanocomposites exhibit remarkable physical properties that are attractive for many applications. These systems have been so far investigated using linear polymer chains; the role of polymer matrix architecture in local dynamics, bulk rheology, and nanoparticle (NP) motion remains unexplored. Here, using quasi-elastic neutron scattering, bulk rheology, and Xray photon correlation spectroscopy, we investigated nanocomposites with spherical silica nanoparticles well dispersed in poly(ethylene oxide) matrices having different architectures (specifically linear, stars, and hyperbranched). The results reveal that the mechanical reinforcement of the nanocomposites with the nonlinear polymers can be altered by orders of magnitude with respect to the conventional nanocomposite with the linear polymer. Polymer compactness and interpenetrability are found to play crucial roles in determining their bulk rheology. At the microscopic level, average segmental dynamics is remarkably slowed down by the attractive NPs in the matrices of high degree of branching, whereas no significant effect is observed in the linear polymer matrix at the same NP loading. In addition, the nanoscale dynamics of particles in the compact nonlinear matrices exhibits strong decoupling from the bulk viscoelasticity, allowing their fast relaxation even at ≈30% by volume. These results provide an experimental evidence that macromolecular architecture is a powerful new tool for tuning the bulk rheological properties as well as the nanoscale dynamics of polymer nanocomposites (PNCs) without the need for changing polymer molecular weight, nanoparticle size, shape, loading, or dispersion state.

Decoding Polymer Architecture Effect on Ion Clustering, Chain Dynamics, and Ionic Conductivity in Polymer Electrolytes

“…Here, β is the stretching exponent and τ is the relaxation time. A delta function and a constant background were also added to account for possible residual immobile fractions and very fast localized motions. , The fitted curves are shown as solid lines on the spectra (note that the elementary Rouse rates for the neat polymers except for HBG6 were reported in our previous work). It was found that β is very close to 0.5 for all samples, confirming that dynamics is due to the curvilinear multimodal motion of the segments along the backbone (i.e., Rouse motion).…”

Polymer architecture effect on rheology and segmental dynamics in poly (methyl methacrylate)-silica nanocomposite melts

“…Polymer nanocomposites (PNCs) with tunable and superior properties are crucial for the development of advanced technologies [ 1 ]. Polymer chains and nanoparticles interact at varying strength and length scales and control the thermo-mechanical properties of PNCs [ 2 – 4 ]. Regarding the nanoparticles (NPs), their chemistry, size, concentration, shape, and state of dispersion play a critical role in the final properties of polymer-nanoparticle composite systems [ 4 – 7 ].…”

“…Polymer chains and nanoparticles interact at varying strength and length scales and control the thermo-mechanical properties of PNCs [ 2 – 4 ]. Regarding the nanoparticles (NPs), their chemistry, size, concentration, shape, and state of dispersion play a critical role in the final properties of polymer-nanoparticle composite systems [ 4 – 7 ]. On the polymer side, molecular weight, chain rigidity, segment packing density, grafting density, and chemical and dynamical heterogeneity are known to influence the local and bulk rheological properties of PNCs [ 2 , 4 , 8 – 10 ].…”

“…Regarding the nanoparticles (NPs), their chemistry, size, concentration, shape, and state of dispersion play a critical role in the final properties of polymer-nanoparticle composite systems [ 4 – 7 ]. On the polymer side, molecular weight, chain rigidity, segment packing density, grafting density, and chemical and dynamical heterogeneity are known to influence the local and bulk rheological properties of PNCs [ 2 , 4 , 8 – 10 ]. The role of chain architecture, which controls the internal dynamics of the polymers and their interaction with NPs, is not well-known.…”

“…A previous study of the authors showed in a PEO/silica composites system that changing polymer chain architecture from linear to hyperbranched and star without altering the total molecular weight, NP concentration, and state of dispersion, slows down the average segmental dynamics of polymer chains, resulting in different levels of mechanical reinforcement in the terminal flow regime, and accelerated nanoscale motion of NPs in the matrices of branched polymers [ 4 ]. However, PEO is a low T g polymer ( T g approximately −47 °C), with a semicrystalline structure with melting temperature T m approximately 65 °C, which makes it difficult to investigate the faster dynamics such as reptation, chain diffusion, and cage relaxations in its melt state.…”