Electro-Optical Device with Tunable Transparency Using Colloidal Core/Shell Nanoparticles

Suspended particle devices (SPDs) adapted for controlling the transmission of electromagnetic radiation have become an area of considerable focus for smart window technology due to their desirable properties, such as instant and precise light control and cost-effectiveness. Here, we demonstrate a SPD with tunable transparency in the visible regime using colloidal assemblies of nanoparticles. The observed transparency using ZnS/SiO₂ core/shell colloidal nanoparticles is dynamically tunable in response to an external electric field with increased transparency when applied voltage increases. The observed transparency change is attributed to structural ordering of nanoparticle assemblies and thereby modifies the photonic band structures, as confirmed by the finite-difference time-domain simulations of Maxwell’s equations. The transparency of the device can also be manipulated by changing the particle size and the device thickness. In addition to transparency, structural colorations and their dynamic tunability are demonstrated using α-Fe₂O₃/SiO₂ core/shell nanomaterials, resulting from the combination of inherent optical properties of α-Fe₂O₃/SiO₂ nanomaterials and coloration due to their tunable structural particle assemblies in response to electric stimuli

Electro-Optical Device with Tunable Transparency Using Colloidal Core/Shell Nanoparticles

Suspended particle devices (SPDs) adapted for controlling the transmission of electromagnetic radiation have become an area of considerable focus for smart window technology due to their desirable properties, such as instant and precise light control and cost-effectiveness. Here, we demonstrate a SPD with tunable transparency in the visible regime using colloidal assemblies of nanoparticles. The observed transparency using ZnS/SiO₂ core/shell colloidal nanoparticles is dynamically tunable in response to an external electric field with increased transparency when applied voltage increases. The observed transparency change is attributed to structural ordering of nanoparticle assemblies and thereby modifies the photonic band structures, as confirmed by the finite-difference time-domain simulations of Maxwell’s equations. The transparency of the device can also be manipulated by changing the particle size and the device thickness. In addition to transparency, structural colorations and their dynamic tunability are demonstrated using α-Fe₂O₃/SiO₂ core/shell nanomaterials, resulting from the combination of inherent optical properties of α-Fe₂O₃/SiO₂ nanomaterials and coloration due to their tunable structural particle assemblies in response to electric stimuli

Electro-Optical Device with Tunable Transparency Using Colloidal Core/Shell Nanoparticles

Suspended particle devices (SPDs) adapted for controlling the transmission of electromagnetic radiation have become an area of considerable focus for smart window technology due to their desirable properties, such as instant and precise light control and cost-effectiveness. Here, we demonstrate a SPD with tunable transparency in the visible regime using colloidal assemblies of nanoparticles. The observed transparency using ZnS/SiO₂ core/shell colloidal nanoparticles is dynamically tunable in response to an external electric field with increased transparency when applied voltage increases. The observed transparency change is attributed to structural ordering of nanoparticle assemblies and thereby modifies the photonic band structures, as confirmed by the finite-difference time-domain simulations of Maxwell’s equations. The transparency of the device can also be manipulated by changing the particle size and the device thickness. In addition to transparency, structural colorations and their dynamic tunability are demonstrated using α-Fe₂O₃/SiO₂ core/shell nanomaterials, resulting from the combination of inherent optical properties of α-Fe₂O₃/SiO₂ nanomaterials and coloration due to their tunable structural particle assemblies in response to electric stimuli

Design Parameters for Subwavelength Transparent Conductive Nanolattices

Recent advancements with the directed assembly of block copolymers have enabled the fabrication over cm² areas of highly ordered metal nanowire meshes, or nanolattices, which are of significant interest as transparent electrodes. Compared to randomly dispersed metal nanowire networks that have long been considered the most promising next-generation transparent electrode material, such ordered nanolattices represent a new design paradigm that is yet to be optimized. Here, through optical and electrical simulations, we explore the potential design parameters for such nanolattices as transparent conductive electrodes, elucidating relationships between the nanowire dimensions, defects, and the nanolattices’ conductivity and transmissivity. We find that having an ordered nanowire network significantly decreases the length of nanowires required to attain both high transmissivity and high conductivity, and we quantify the network’s tolerance to defects in relation to other design constraints. Furthermore, we explore how both optical and electrical anisotropy can be introduced to such nanolattices, opening an even broader materials design space and possible set of applications

Ignition and Combustion Characteristics of Nanoaluminum with Copper Oxide Nanoparticles of Differing Oxidation State

The importance of the oxidation state of an oxidizer and its impact on gaseous oxygen and total gas production in nanocomposite thermite combustion was investigated by probing the reaction and ignition properties of aluminum nanoparticles (Al-NPs) with both cupric oxide (CuO) and cuprous oxide (Cu₂O) nanoparticles. The gas release and ignition behavior of these materials were tested with >10⁵ K/s temperature jump (T-jump) heating pulses in a high temporal resolution time-of-flight mass spectrometer (ToF-MS) as well as in an argon environment. Reactivity was tested using a constant volume combustion cell with simultaneous pressure and optical measurements. A variety of Cu₂O particle sizes ranging from 200 to 1500 nm were synthesized and found to release oxygen at ∼1200 K, which is higher than the values found for a variety of CuO particle sizes (∼1000 K). Both oxides were found to ignite around 1000 K, which implies a consistent ignition mechanism for both through a condensed phase pathway. The higher oxidation state (CuO) thermites were found to react faster and produce higher pressures by several orders of magnitude, which implies that gaseous species play a critical role in the combustion process. Differences in reactivity between argon and vacuum environments and the use of Cu diluent to simulate Cu₂O suggest that it is the intermediate product gas, O₂, that plays the most significant role in combustion as an enabler of heat transfer and a secondary oxidizer. The lack of any oxidizer size dependence on ignition is suggestive of rapid sintering that wipes out the effect of enhanced interfacial contact area for smaller oxidizers

Supercapacitors Based on Three-Dimensional Hierarchical Graphene Aerogels with Periodic Macropores

Graphene is an atomically thin, two-dimensional (2D) carbon material that offers a unique combination of low density, exceptional mechanical properties, thermal stability, large surface area, and excellent electrical conductivity. Recent progress has resulted in macro-assemblies of graphene, such as bulk graphene aerogels for a variety of applications. However, these three-dimensional (3D) graphenes exhibit physicochemical property attenuation compared to their 2D building blocks because of one-fold composition and tortuous, stochastic porous networks. These limitations can be offset by developing a graphene composite material with an engineered porous architecture. Here, we report the fabrication of 3D periodic graphene composite aerogel microlattices for supercapacitor applications, via a 3D printing technique known as direct-ink writing. The key factor in developing these novel aerogels is creating an extrudable graphene oxide-based composite ink and modifying the 3D printing method to accommodate aerogel processing. The 3D-printed graphene composite aerogel (3D-GCA) electrodes are lightweight, highly conductive, and exhibit excellent electrochemical properties. In particular, the supercapacitors using these 3D-GCA electrodes with thicknesses on the order of millimeters display exceptional capacitive retention (ca. 90% from 0.5 to 10 A·g^–1) and power densities (>4 kW·kg^–1) that equal or exceed those of reported devices made with electrodes 10–100 times thinner. This work provides an example of how 3D-printed materials, such as graphene aerogels, can significantly expand the design space for fabricating high-performance and fully integrable energy storage devices optimized for a broad range of applications

Supercapacitors Based on Three-Dimensional Hierarchical Graphene Aerogels with Periodic Macropores

Graphene is an atomically thin, two-dimensional (2D) carbon material that offers a unique combination of low density, exceptional mechanical properties, thermal stability, large surface area, and excellent electrical conductivity. Recent progress has resulted in macro-assemblies of graphene, such as bulk graphene aerogels for a variety of applications. However, these three-dimensional (3D) graphenes exhibit physicochemical property attenuation compared to their 2D building blocks because of one-fold composition and tortuous, stochastic porous networks. These limitations can be offset by developing a graphene composite material with an engineered porous architecture. Here, we report the fabrication of 3D periodic graphene composite aerogel microlattices for supercapacitor applications, via a 3D printing technique known as direct-ink writing. The key factor in developing these novel aerogels is creating an extrudable graphene oxide-based composite ink and modifying the 3D printing method to accommodate aerogel processing. The 3D-printed graphene composite aerogel (3D-GCA) electrodes are lightweight, highly conductive, and exhibit excellent electrochemical properties. In particular, the supercapacitors using these 3D-GCA electrodes with thicknesses on the order of millimeters display exceptional capacitive retention (ca. 90% from 0.5 to 10 A·g^–1) and power densities (>4 kW·kg^–1) that equal or exceed those of reported devices made with electrodes 10–100 times thinner. This work provides an example of how 3D-printed materials, such as graphene aerogels, can significantly expand the design space for fabricating high-performance and fully integrable energy storage devices optimized for a broad range of applications

On-Demand and Location Selective Particle Assembly via Electrophoretic Deposition for Fabricating Structures with Particle-to-Particle Precision

Programmable positioning of 2 μm polystyrene (PS) beads with single particle precision and location selective, “on-demand”, particle deposition was demonstrated by utilizing patterned electrodes and electrophoretic deposition (EPD). An electrode with differently sized hole patterns, from 0.5 to 5 μm, was used to illustrate the discriminatory particle deposition events based on the voltage and particle-to-hole size ratio. With decreasing patterned hole size, a larger electric field was required for a particle deposition event to occur in that hole. For the 5 μm hole, particle deposition began to occur at 10 V/cm where as an electric field of 15 V/cm was required for particles to begin depositing in the 2 μm holes. The likelihood of particle depositions continued to increase for smaller sized holes as the electric field increased. Eventually, a monolayer of particles began to form at approximately 20 V/cm. In essence, a voltage threshold was found for each hole pattern of different sizes, allowing fine adjustments in pattern hole size and voltage to control when a particle deposition event took place, even with the patterns on the same electrode. This phenomenon opens a route toward controlled, multimaterial deposition and assembly onto substrates without repatterning of the electrode or complicated surface modification of the particles. An analytical approach using the theories for electrophoresis and dielectrophoresis found the former to be the dominating force for depositing a particle into a patterned hole. Ebeam lithography was used to pattern spherical holes in precise configurations onto electrode surfaces, where each hole accompanied a polystyrene (PS) particle placement and attachment during EPD. The versatility of e-beam lithography was utilized to create arbitrary pattern configurations to fabricate particle assemblies of limitless configurations, enabling fabrication of unique materials assemblies and interfaces

Cooperative Reorganization of Mineral and Template during Directed Nucleation of Calcium Carbonate

Self-assembled monolayers (SAMs) prepared from organic thiol molecules on metal substrates are known to exert substantial influence over mineralization and, as such, provide model systems for investigating the mechanisms of templated crystallization by organic matrices. Characterizing the structural evolution at the organic/inorganic interface in SAM/crystal systems is of paramount importance in understanding these mechanisms. In this study, X-ray absorption spectroscopy is used to characterize the structural evolution of SAMs prepared from purpose-synthesized organic thiols, with similar yet subtly different structures and compositions, during the course of mineralization at their surfaces. The studies reveal that the structure of the thiol molecules strongly affects their ability to reorient within the SAM. Complementary scanning electron microscopy measurements demonstrate that this feature of the SAMs is strongly correlated with the capability of the monolayers to induce preferential ordering among the organic crystals. Consistent with recent modeling studies of SAM/crystal systems, these findings provide experimental evidence that structural flexibility within the SAMs is crucial for achieving templated crystallization and that templating is inherently a cooperative process that selects the most favorable combination of SAM and crystal orientations

Ultralight Conductive Silver Nanowire Aerogels

Low-density metal foams have many potential applications in electronics, energy storage, catalytic supports, fuel cells, sensors, and medical devices. Here, we report a new method for fabricating ultralight, conductive silver aerogel monoliths with predictable densities using silver nanowires. Silver nanowire building blocks were prepared by polyol synthesis and purified by selective precipitation. Silver aerogels were produced by freeze-casting nanowire aqueous suspensions followed by thermal sintering to weld the nanowire junctions. As-prepared silver aerogels have unique anisotropic microporous structures, with density precisely controlled by the nanowire concentration, down to 4.8 mg/cm³ and an electrical conductivity up to 51 000 S/m. Mechanical studies show that silver nanowire aerogels exhibit “elastic stiffening” behavior with a Young’s modulus up to 16 800 Pa