We investigated the dynamics of gold nanoparticles (NPs) within an entangled liquid of poly(n-butyl methacrylate) (PBMA) above the glass transition temperature (T g ). The experiments were performed by using a modified version of fluctuation correlation spectroscopy (FCS), which measured the translational diffusion (D) of the isolated NPs as a function of their size (2R 0 = 5−20 nm) and temperature (T). We probed the most interesting but sparsely investigated length regime where the particle size/tube diameter (d t ) ratio ranges between ∼1−4. This allowed us to put into direct test recently developed theories and simulations. By measuring the bulk viscosity of the melt, the ratio D/D SE was determined, where D SE is the continuum prediction from Stokes− Einstein (SE) relation. Our results indicate gradual recovery to SE behavior and full coupling to entanglement relaxation would require 2R 0 ≈ 7−10d t .

Gold nanoparticles are used as a luminescent contrast agent to study size-dependent dynamics in polymer matrix. The experiments measured the diffusion coefficient of particles in poly͑butyl methacrylate͒ melt by tracking their motion within a diffraction-limited focus of a laser with 150 fs pulses at 800 nm. Our results indicate that for unentangled polymers, when the particle radius ͑R͒ is greater than the gyration radius ͑R g ͒ of the chain, the Stokes-Einstein relation can accurately predict particle dynamics. For longer chains, if the entanglement mesh length is larger than R, the particle diffuses ϳ250 times faster than predicted by the Stokes-Einstein relation.

Demands to increase the stored energy density of electrostatic capacitors have spurred the development of materials with enhanced dielectric breakdown, improved permittivity, and reduced dielectric loss. Polymer nanocomposites (PNCs), consisting of a blend of amorphous polymer and dielectric nanofillers, have been studied intensely to satisfy these goals; however, nanoparticle aggregates, field localization due to dielectric mismatch between particle and matrix, and the poorly understood role of interface compatibilization have challenged progress. To expand the understanding of the inter-relation between these factors and, thus, enable rational optimization of low and high contrast PNC dielectrics, we compare the dielectric performance of matrix-free hairy nanoparticle assemblies (aHNPs) to blended PNCs in the regime of low dielectric contrast to establish how morphology and interface impact energy storage and breakdown across different polymer matrices (polystyrene, PS, and poly(methyl methacrylate), PMMA) and nanoparticle loadings (0-50% (v/v) silica). The findings indicate that the route (aHNP versus blending) to well-dispersed morphology has, at most, a minor impact on breakdown strength trends with nanoparticle volume fraction; the only exception being at intermediate loadings of silica in PMMA (15% (v/v)). Conversely, aHNPs show substantial improvements in reducing dielectric loss and maintaining charge/discharge efficiency. For example, low-frequency dielectric loss (1 Hz-1 kHz) of PS and PMMA aHNP films was essentially unchanged up to a silica content of 50% (v/v), whereas traditional blends showed a monotonically increasing loss with silica loading. Similar benefits are seen via high-field polarization loop measurements where energy storage for ∼15% (v/v) silica loaded PMMA and PS aHNPs were 50% and 200% greater than respective comparable PNC blends. Overall, these findings on low dielectric contrast PNCs clearly point to the performance benefits of functionalizing the nanoparticle surface with high-molecular-weight polymers for polymer nanostructured dielectrics.

We studied the diffusion of gold nanoparticles in semidilute and entangled solutions of polystyrene (PS) in toluene using fluctuation correlation spectroscopy (FCS). The polymer concentration was varied from approximately 6c* to 20c*, where c* is the overlap concentration. In our experiments, the particle radius (R approximately 2.5 nm) was much smaller compared to the radius of gyration (Rg approximately 18 nm) of the chain but comparable to the average mesh size (xi) of the fluctuating polymer network. The diffusion coefficient (D) of the particles decreased monotonically with polymer concentration and it can be fitted with a stretched exponential function, D=D0 exp(-microcnu), with the value of the scaling parameter, nu approximately 0.9. At high concentration of the polymer, a clear subdiffusive motion of the particles was observed. The results were compared with the diffusion of free dyes (coumarin 480), which showed normal diffusive behavior for all concentrations.

Next-generation nanoelectronics based on 2D materials ideally will require reliable, fl exible, transparent, and versatile dielectrics for transistor gate barriers, environmental passivation layers, capacitor spacers, and other device elements. Ultrathin amorphous boron nitride of thicknesses from 2 to 17 nm, described in this work, may offer these attributes, as the material is demonstrated to be universal in structure and stoichiometric chemistry on numerous substrates including fl exible polydimethylsiloxane, amorphous silicon dioxide, crystalline Al 2 O 3 , other 2D materials including graphene, 2D MoS 2 , and conducting metals and metal foils. The versatile, large area pulsed laser deposition growth technique is performed at temperatures less than 200 °C and without modifying processing conditions, allowing for seamless integration into 2D device architectures. A device-scale dielectric constant of 5.9 ± 0.65 at 1 kHz, breakdown voltage of 9.8 ± 1.0 MV cm −1 , and bandgap of 4.5 eV were measured for various thicknesses of the ultrathin a -BN material, representing values higher than previously reported chemical vapor deposited h -BN and nearing single crystal h -BN.

Rapid fabrication of large area, ordered assemblies of polymer grafted (hairy) nanoparticles (PGNs) will enable additive manufacturing of novel membrane, electronic, and photonic elements. Herein, we discuss the relationship between select processing conditions, substrate surface energy, and canopy architecture on the hierarchical structure of sub- to monolayer PGN assemblies. Varying concentrations (10, 20, and 70 nM) of polystyrene (PS) grafted (σ ∼ 1 chain/nm2) gold nanoparticles (AuNP, r 0 = 9 nm) were flow-coated onto surface-modified silicon wafers (γs ∼ 20 mN/m, hydrophobic to 80 mN/m, hydrophilic). The profile of an isolated gold–polystyrene (PS) PGN depends on substrate–canopy interface energy. At low substrate–PS interface energy (20 mN/m), the PS canopy spreads to maximize contact with the surface, whereas at high substrate–PS interface energy (80 mN/m), the chains minimize contact area resulting in a more compact, thicker PGN corona. This behavior is translated up to monolayer assemblies, where rougher, less-ordered assemblies with smaller AuNP–surface separation form on substrates with low interface energy. These films are also thinner with greater Au volume fraction, indicating that the segment density within the PS canopy depends on substrate surface energy. The impact of these processing parameters on PGN film formation parallels classic colloidal deposition even though the PS concentration is within the Landau–Levich regime for film formation from linear chains. The factors influencing local morphology, however, resemble those that affect polymer thin films. Using this understanding, we demonstrate fabrication within seconds of large area monolayer films with close-packed order.

Emerging needs for fast charge/discharge yet high-power, lightweight, and flexible electronics requires the use of polymer-film-based solid-state capacitors with high energy densities. Fast charge/discharge rates of film capacitors on the order of microseconds are not achievable with slower charging conventional batteries, supercapacitors and related hybrid technologies. However, the current energy densities of polymer film capacitors fall short of rising demand, and could be significantly enhanced by increasing the breakdown strength (EBD) and dielectric permittivity (εr) of the polymer films. Co-extruded two-homopolymer component multilayered films have demonstrated much promise in this regard showing higher EBD over that of component polymers. Multilayered films can also help incorporate functional features besides energy storage, such as enhanced optical, mechanical, thermal and barrier properties. In this work, we report accomplishing multilayer, multicomponent block copolymer dielectric films (BCDF) with soft-shear driven highly oriented self-assembled lamellar diblock copolymers (BCP) as a novel application of this important class of self-assembling materials. Results of a model PS-b-PMMA system show ∼50% enhancement in EBD of self-assembled multilayer lamellar BCP films compared to unordered as-cast films, indicating that the breakdown is highly sensitive to the nanostructure of the BCP. The enhancement in EBD is attributed to the "barrier effect", where the multiple interfaces between the lamellae block components act as barriers to the dielectric breakdown through the film. The increase in EBD corresponds to more than doubling the energy storage capacity using a straightforward directed self-assembly strategy. This approach opens a new nanomaterial paradigm for designing high energy density dielectric materials.

The ultimate energy storage performance of an electrostatic capacitor is determined by the dielectric characteristics of the material separating its conductive electrodes. Polymers are commonly employed due to their processability and high breakdown strength; however, demands for higher energy storage have encouraged investigations of ceramic-polymer composites. Maintaining dielectric strength, and thus minimizing flaw size and heterogeneities, has focused development toward nanocomposite (NC) films; but results lack consistency, potentially due to variations in polymer purity, nanoparticle surface treatments, nanoparticle size, and film morphology. To experimentally establish the dominant factors in broad structure-performance relationships, we compare the dielectric properties for four high-purity amorphous polymer films (polymethyl methacrylate, polystyrene, polyimide, and poly-4-vinylpyridine) incorporating uniformly dispersed silica colloids (up to 45% v/v). Factors known to contribute to premature breakdown-field exclusion and agglomeration-have been mitigated in this experiment to focus on what impact the polymer and polymer-nanoparticle interactions have on breakdown. Our findings indicate that adding colloidal silica to higher breakdown strength amorphous polymers (polymethyl methacrylate and polyimide) causes a reduction in dielectric strength as compared to the neat polymer. Alternatively, low breakdown strength amorphous polymers (poly-4-vinylpyridine and especially polystyrene) with comparable silica dispersion show similar or even improved breakdown strength for 7.5-15% v/v silica. At ∼15% v/v or greater silica content, all the polymer NC films exhibit breakdown at similar electric fields, implying that at these loadings failure becomes independent of polymer matrix and is dominated by silica.