No abstract

Matrix free assemblies of polymer‐grafted, “hairy” nanoparticles (aHNP) exhibit novel morphology, dielectric, and mechanical properties, as well as providing means to overcome dispersion challenges ubiquitous to conventional polymer‐inorganic nanocomposite blends. Physical aging of the amorphous polymer glass between the close‐packed nanoparticles (NPs) will dominate long‐term stability; however, the energetics of volume recovery within the aHNPs is unknown. Herein, we compare glass transition temperature (Tg) and enthalpy recovery of aHNPs to NP‐polymer blends, across different nano‐silica loadings (0–50 v/v%) and canopy architecture of polystyrene (PS) grafted silica. For aHNPs, the grafting of PS to silica imposes an additional design constraint between silica volume fraction, graft density, and graft molecular weight. At low and intermediate silica volume fraction, the Tg of blended nanocomposites is independent of silica content, reflecting a neutral polymer‐NP interface. For aHNPs, the Tg decreases with silica content, implying that chain tethering decreases local segment density more than the effect of molecular weight or polymer‐NP interactions. Additionally, the Tg of the aHNPs is higher than a linear matrix of comparable molecular weight, implying a complementary effect to local segment density that constrains cooperativity. In contrast, enthalpy recovery rate in the blend or aHNP glass is retarded comparably. In addition, a cross‐over temperature, Tx, emerges deep within the glass where the enthalpy recovery process of all nanocomposites becomes similar to linear unfilled matrices. Differences between structural recovery in aHNP and blended nanocomposites occur only at the highest silica loadings (∼ 50 v/v%), where enthalpy recovery for aHNPs is substantially suppressed relative to the blended counterparts. The absence of physical aging at these loadings is independent of brush architecture (graft density or molecular weight of tethered chains) and indicates that the impact of chain tethering on effective bulk structural relaxation starts to appear at particle‐particle surface separations on the order of the Kuhn length. Overall, these observations can be understood within the context of how three separate structural characteristics impact local segment density and relaxation processes: the dimension and architecture of the tethered polymer chains, the separation between NP surfaces, and the confinement imposed by chain tethering and space filling within the aHNP. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 319–330

We have studied the electronic characteristics of chemically modified single-walled carbon nanotubes by oxygen doping using first-principles density-functional calculations. The oxygen doping, a controlled [2 + 1] cycloaddition scheme, is shown to modify the π-conjugation and impact on the near-infrared band gaps. The implications of tailoring the electronic structure of oxygen doped carbon nanomaterials for future device applications are discussed.

Hairy core–shell nanoparticles have emerged as a unique class of polymeric nanocomposites. Hairy nanoparticles (HNPs) with hard polystyrene (PS) cores and soft polydimethylsiloxane (PDMS) shells have been synthesized by living anionic polymerization via “one‐pot synthesis” approach. The size and composition of both core and shell components can be controlled. The synthetic approach produces an entirely new class of HNPs. Differential scanning calorimetry thermograms of the core–shell nanoparticles show two distinct transition temperatures corresponding to a glass transition temperature (Tg) of PS segment and a melting transition temperature (Tm) of PDMS segment indicating the formation of a phase separated system. The synthesized HNPs show different morphologies dependent on the content of PDMS due to the fusion of particles. Solvents play a crucial role in the fusion of particles. Diethyl ether can reduce the fusion of particles and generate almost uniform particles. The HNPs can self‐assemble into hierarchical suprastructures. The HNPs may have potential applications in emerging industries such as high‐density microelectronic materials and lithography.

Nanocomposites are of increasing interest due to their unique structural, electronic, and thermal properties. Simultaneously, multiscale molecular modeling is becoming more robust. Therefore computational models are able to be examined with increased accuracy, complexity, and dimension. Graphene based molecules are lauded for their conductive properties as well as their architecture-like geometry which may allow bottom up nanoscale fabrication of nanoscopic structures. Furthermore, these macrocycled molecules allow high interactivity with other molecules including highly tensiled polymers that yield other novel supramolecular structures when interacted. These supramolecular structures are being investigated in lieu of a variety of potential applications. Nanocomposites of cured epoxy resin reinforced by single-walled carbon nanotubes exhibit a plethora of interesting behavior at the molecular level. A fundamental issue is how the self-organized dynamic structure of functional molecular systems affects the interactions of the nano-reinforced composites. A combination of force-field based molecular dynamics and local density-functional calculations shows that the stacking between the aromatic macrocycle and the surface of the SWNTs manifests itself via increased interfacial binding. First-principles calculations on the electronic structures further reveal that there exists distinct level hybridization behavior for metallic and semiconducting nanotubes. In addition there is a monatomic increase in binding energy with an increase in the nanotube diameter. The simulation studies suggest that graphene nanoplatelets are potentially the best fillers of epoxy matrices. The implications of these results for understanding dispersion mechanism and future nanocomposite developments are discussed.