Abstract
The linear elastic properties of isotropic materials of polymer tethered nanoparticles (NPs) are evaluated using noncontact Brillouin light spectroscopy. While the mechanical properties of dense brush materials follow predicted trends with NP composition, a surprising increase in elastic moduli is observed in the case of sparsely grafted particle systems at approximately equal NP filling ratio. Complementary molecular dynamics simulations reveal that the stiffening is caused by the coil-like conformations of the grafted chains, which lead to stronger polymer–polymer interactions compared to densely grafted NPs with short chains. Our results point to novel opportunities to enhance the physical properties of composite materials by the strategic design of the “molecular architecture” of constituents to benefit from synergistic effects relating to the organization of the polymer component.
Highlights
Complementary molecular dynamics simulations reveal that the stiffening is caused by the coil-like conformations of the grafted chains, which lead to stronger polymer−polymer interactions compared to densely grafted NPs with short chains
O ver the last few decades, extensive studies validated the enhancement of the mechanical properties of polymer composites through the incorporation of nanoparticle (NP) fillers into the polymer matrix.[1−3] the details of this reinforcement in two-component nanocomposite systems remain an open question, experiments have suggested that it originates from the subtle interplay of interactions between polymer and particle constituents and spatial confinement.[4−6] In the solid state, the uniform spatial dispersion of NPs is crucial for attaining optimal mechanical response.[7]
The one-component nanocomposite systems used in this study consist of PS grafted silica particles with varying grafting density, σ, and degree of polymerization (DP), N, below and above the entanglement value of bulk PS
Summary
Letter brush layers[17,19] and pronounced slowdown of local dynamics at the interface.[20]. We utilized Brillouin light spectroscopy, a noncontact and nondestructive technique, to measure the longitudinal and transverse sound velocities and obtain the elastic engineering moduli (Young’s, bulk, and shear modulus) of isotropic materials of polystyrene tethered (silica) nanoparticles (NPs) (core radius 57 ± 3 nm) with different length and density of grafted chains. All elastic moduli of the dense brush materials (≈ 0.5 chains/nm2) increase with NP filling ratio, following predictions from effective medium theory Both the longitudinal and shear modulus increase significantly (by about 30%) in the case of a sparsely grafted (0.08 chains/nm2) NP system at approximately equal NP filling (φPS ≈ 0.48).
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