High Loading Fractions Research Articles

Dielectric Elastomers with Liquid Metal and Polydopamine-Coated Graphene Oxide Inclusions.

Suspending microscale droplets of liquid metals like eutectic gallium-indium (EGaIn) in polydimethylsiloxane (PDMS) has been shown to dramatically enhance electrical permittivity without sacrificing the elasticity of the host PDMS matrix. However, increasing the dielectric constant of EGaIn-PDMS composites beyond previously reported values requires high EGaIn loading fractions (>50% by volume) that can result in substantial increases in density and loss of material integrity. In this work, we enhance permittivity without further increasing EGaIn loading by incorporating polydopamine (PDA)-coated graphene oxide (GO) and partially reduced GO. In particular, we show that the combination of EGaIn and PDA-GO within a PDMS matrix results in an elastomer composite with a high dielectric constant (∼10-57), a low dissipation factor (∼0.01), and rubber-like compliance and elasticity.

Water Dynamics in Competitive Solvation Assisted Loading of Colloidal Curcumin Nanoparticles onto Mesoporous Silica Nanostructures (Part. Part. Syst. Charact. 8/2022)

In article number 2200062, Nitthin Ananth, Jose, and co-workers studied that the sequential solvent evaporation approach combined with dielectric nano environment tuning mediates the uploading of hydrophobic curcumin nanoparticles onto mesoporous silica. The co-solvents that modulate the water dynamics favor the form of monodispersed, stable nanostructures with high loading fractions.

Self-Assembling Allochroic Nanocatalyst for Improving Nanozyme-Based Immunochromatographic Assays

Paper-based rapid diagnostic tests, such as immunochromatographic assays, namely lateral flow immunoassay (LFA), are valuable alternatives for biomarker detection compared to traditional laboratory-based tests, but these assays need further refinement to consolidate their biosensing capabilities. Nanozyme integration into LFA systems may provide a reliable means of improving the analytic sensitivity of LFA tests. Due to the involvement of multiple liquid-handling steps, the quantitative accuracy is compromised, hence hindering the use of untrained personnel point-of-care use. Self-assembling allochroic nanocatalyst (SAN) assemblies satisfy these LFA quality measures by optimizing analyte-antibody reporting performance and by intrinsically catalyzing chromogen activation, thereby reducing the number of liquid handling steps involved during sample analysis. In SANs, the hydrophobic chromogens serve as peroxidase substrates that self-assemble into nanoparticles at high loading fractions. These features demonstrate the potential for SAN-LFAs to be a valuable patient point-of-care (POC) test. Herein, we describe the SAN fabrication process and employ SAN-LFAs to detect cardiac troponin I-troponin C (cTnI-TnC) and myoglobin (Myo) levels present in plasma samples. Using SAN-LFAs, the limits of detection for cTnI-TnC and Myo were 0.012 ng/mL and 0.2 ng/mL respectively. We also demonstrate SAN compatibility with blood samples and stability under long-term storage conditions. The successful utlization of SANs in LFA-based biomarker detection may inspire these nanocatalysts to be integrated into similar immunochromatographic testing methods.

3-D Edge-Oriented Electrocatalytic NiCo 2 S 4 Nanoflakes on Vertical Graphene for Li-S Batteries

Polysulfide shuttle effect, causing extremely low Coulombic efficiency and cycling stability, is one of the toughest challenges hindering the development of practical lithium sulfur batteries (LSBs). Introducing catalytic nanostructures to stabilize the otherwise soluble polysulfides and promote their conversion to solids has been proved to be an effective strategy in attacking this problem, but the heavy mass of catalysts often results in a low specific energy of the whole electrode. Herein, by designing and synthesizing a free-standing edge-oriented NiCo 2 S 4 /vertical graphene functionalized carbon nanofiber (NCS/EOG/CNF) thin film as a catalytic overlayer incorporated in the sulfur cathode, the polysulfide shuttle effect is largely alleviated, revealed by the enhanced electrochemical performance measurements and the catalytic function demonstration. Different from other reports, the NiCo 2 S 4 nanosheets synthesized here have a 3-D edge-oriented structure with fully exposed edges and easily accessible in-plane surfaces, thus providing a high density of active sites even with a small mass. The EOG/CNF scaffold further renders the high conductivity in the catalytic structure. Combined, this novel structure, with high sulfur loading and high sulfur fraction, leads to high-performance sulfur cathodes toward a practical LSB technology.

Ultrahigh thermally conductive graphene filled liquid crystalline epoxy composites: Preparation assisted by polyethylene glycol

How to prepare high thermal conductive epoxy composites is still a challenge. In this work, polyethylene glycol (PEG) is introduced to the interface of liquid crystalline epoxy/graphene composite (EO/GR) as a route to ultrahigh thermally conductive yet mechanically robust nanocomposites. Assisted by PEG, the EO/GR composite is prepared by a simple blending method. The thermal conductivity of the prepared composite can reach to 10.17 W m−1 K−1, and its electromagnetic interference shielding effectiveness (EMI SE) shielding efficiency is about 50 dB. The ultrahigh thermally conductive composite is mechanically robust and thermal stable. The ultrahigh thermal conductivity of the composite might be originated from the improved interfacial compatibility between EO and GR, which facilitates the successful preparation of composite at a high loading fraction of GR. Highly filled graphene in the matrix makes it possible to form massive GR-GR thermal conductive paths, which contribute to the ultrahigh thermal conductivity of the composite. This work provides an effective and simple method to prepare ultrahigh thermally conductive yet mechanically robust epoxy composites.

Additive manufacturing of highly dense anisotropic Nd–Fe–B bonded magnets

Extrusion based big area additive manufacturing process is utilized for fabrication of dense anisotropic bonded magnets. High loading fraction (≥70 vol%) of magnequench anisotropic Nd–Fe–B powder in nylon is used for preparing anisotropic bonded magnets. A higher energy product of ~143.2 kJ/m3 is obtained for the post printed magnetic field aligned at 1 Tesla. These findings make an important step towards the fabrication of gap magnets with energy product between ferrite and Nd–Fe–B sintered magnets. Moreover, printed bonded magnets exhibited better thermal stability, mechanical properties and superior magnetic properties compared to commercial injection molded magnets.

Experimental and numerical study of air-water mist jet impingement cooling on a cylinder

The paper presents the study of experimental as well as the numerical study of air-water mist jet impingement cooling over a heated cylinder in the non-boiling region. The studies are conducted for various mist loading fraction, f = 0.0025, 0.0050, 0.0075 and 0.01; Reynolds number, Remix.=8000, 10,500, 13,000 and 15,500; and surface-to-nozzle spacing, H/d = 30, 40, 50 and 60. Enhancement in the heat transfer (η) for mist jet impingement as compared to air jet impingement is obtained from experimental and numerical analysis. The numerical study also helped in understanding the distribution and tracking of droplets in the computational domain. High enhancement in the heat transfer is observed with high mist loading fraction. Also, the lowest Reynolds number yielded the highest enhancement in heat transfer with comparison to the higher Reynolds number. At various surface-to-nozzle spacing, the enhancement in heat transfer is high for low surface-to-nozzle spacing near the stagnation zone to a certain point, after which point the enhancement reverses as higher enhancement in heat transfer is observed for high surface-to-nozzle spacing. As high as 408% and 775% enhancement in the heat transfer at the stagnation point is observed for f = 0.01, Remix.= 8000and H/d = 30 during experimental and numerical analysis respectively. The correlation has been proposed to estimate the enhancement in heat transfer at the stagnation point.

Synthesis of Highly Luminescent Carbon Dots@Polyacrylate Sodium Composites with High Loading Fraction and Their Application in Light-Emitting Diodes †

Synthesis of Highly Luminescent Carbon Dots@Polyacrylate Sodium Composites with High Loading Fraction and Their Application in Light-Emitting Diodes †

CdSe/CdS–poly(cyclohexylethylene) thin film luminescent solar concentrators

Thin film luminescent solar concentrators are promising components of distributed power generation systems for building integrated photovoltaic applications. However, thin film geometries require high luminophore loading fractions to achieve sufficient absorption of sunlight, which, in the case of nanocrystal luminophores, can lead to aggregation and light scattering. In this work, we integrate CdSe/CdS nanocrystals into thin films of poly(cyclohexylethylene) at a range of loading fractions and characterize the composites with a combination of spectroscopic and simulation tools. We find that increased incident sunlight scattering is observed for the increasing luminophore loading fraction, but that the scattering is mostly limited to higher energy sunlight such that visible transmittance and haze of the samples are all greater than 89.7% and less than 8.3%, respectively. We then analyze the refractive index of the composite and show that the increase in loading fraction also affects the propagation of photoluminescence in the film, especially if the refractive index of the film is greater than that of the substrate. These studies show the importance of understanding the optical transport within thin films and provide design criteria to fabricate thin films for future implementation into building integrated photovoltaic applications.

Quenching‐Resistant Polymer Carbon Dot Preserving Emission Color Consistency in Solid‐State

AbstractSolid‐state luminescent carbon dot without dispersion matrices is studied to overcome aggregation‐caused quenching, but it usually shows spectral shift between solution‐ and solid‐state accompanying a dramatic decrease of fluorescence intensity, which hinders a real application. Herein, polymer carbon dot (PCD) showing solid‐state luminescence without red‐shift is synthesized by low‐temperature reaction. The PCD solution and solid have the same emission peaks at 434 nm and similar absolute quantum yields of 68.2% and 62.7%, respectively, which is uncommon feature compared to other carbon dots. The mechanism for solid‐state luminescence and emission color consistency is investigated by structural analysis of the PCD compared to carbon dot that shows red‐shift in solid‐state. The PCD is utilized into light‐emitting diode application as a phosphor, and little color change in emission without significant decrease in luminous efficacy is achieved even with high loading fraction (50 wt%), opening the possibility of real application in solid‐state lighting.

Intrinsic Insertion Limits of Graphene Oxide into Epoxy Resin and the Dielectric Behavior of Composites Comprising Truly 2D Structures

The composites of graphene oxide (GO) with epoxy resin were prepared via the homogeneous liquid phase transfer method, allowing uniform distribution and nearly fully exfoliated condition of GO in the matrix. The ∼0.6% GO content is the absolute maximum that can be inserted into the epoxy matrix (at the flakes’ size 5–20 μm) without sacrificing the exfoliation level of the 2D filler and the uniformity of the composition. Curing at 180 °C causes the in situ disproportionation, or so-called “thermal reduction” of GO in the matrix. The as-induced conductivity of GO flakes alters dielectric properties of composites via the Maxwell–Wagner polarization. For the first time, we experimentally demonstrate the dielectric properties of composite materials comprising truly 2D single-atomic-layer structures. They exhibit relatively low permittivity values that reach saturation at ∼0.2% filling fraction, and classical relaxation peaks on the imaginary part function at 0.3–0.4% GO content. The presented experimental data strongly suggest that the Maxwell–Wagner polarization is sufficiently suppressed in composites comprising truly 2D structures because of their interaction with the matrix. On the contrary, high permittivity values, reported simultaneously with the high loading fractions (>0.6% at the flakes’ size 5–20 μm), are indicative of the nonsingle-layer character and/or the aggregation of the 2D inclusion particles in the polymer matrix.

Fabrication of highly dense isotropic Nd-Fe-B nylon bonded magnets via extrusion-based additive manufacturing

Magnetically isotropic bonded magnets with a high loading fraction of 70 vol.% Nd-Fe-B are fabricated via an extrusion-based additive manufacturing, or 3D printing system that enables rapid production of large parts. The density of the printed magnet is ∼ 5.2 g/cm3. The room temperature magnetic properties are: intrinsic coercivity Hci = 8.9 kOe (708.2 kA/m), remanence Br = 5.8 kG (0.58 T), and energy product (BH)max = 7.3 MGOe (58.1 kJ/m3). The as-printed magnets are then coated with two types of polymers, both of which improve the thermal stability as revealed by flux aging loss measurements. Tensile tests performed at 25 °C and 100 °C show that the ultimate tensile stress (UTS) increases with increasing loading fraction of the magnet powder, and decreases with increasing temperature. AC magnetic susceptibility and resistivity measurements show that the 3D printed Nd-Fe-B bonded magnets exhibit extremely low eddy current loss and high resistivity. Finally, we demonstrate the performance of the 3D printed magnets in a DC motor configuration via back electromotive force measurements.

Conquering Aggregation-Induced Solid-State Luminescence Quenching of Carbon Dots through a Carbon Dots-Triggered Silica Gelation Process

Aggregation-induced luminescence quenching of carbon dots (CDots) is the main obstacle for their applications in the solid state. Herein, we report a method to produce strongly luminescent CDots@silica composite gels with highly concentrated emitting centers, where the gelation of tetraethyl orthosilicate is initiated by the surface hydroxyl groups of CDots. The key feature of this approach is to prevent both the collision between high concentrated CDots in gelating solution and their aggregation upon drying. The resultant CDots@silica composite xerogel exhibits both high CDots loading fraction (19.2 wt %) and photoluminescence quantum yields (>40%).

High thermal conductivity and temperature probing of copper nanowire/upconversion nanoparticles/epoxy composite

Epoxy resin has been intensively used as an electronic packaging material for its good mechanical strength and electrical insulativity. However, the low thermal conductivity of epoxy resin limits its applications. Inorganic fillers with a high loading fraction (>30 vol%) is typically used to enhance the thermal conductivity. But the high loading fraction could degrade the mechanical property and challenge the processing. In this work, we develop a new class of epoxy composites comprising very long (up to tens of micrometers) single-crystalline copper nanowires (a diameter of ∼20 nm and a length of up to ∼40 μm) as filler. A high thermal conductivity of 2.59 W/mK was obtained at a very low loading fraction of Cu nanowires at 0.12 vol%, corresponding to an 8-fold enhancement in thermal conductivity of plain epoxy resins. We also demonstrate that ytterbium and erbium codoped sodium yttrium tetra-fluoride (NaYF4:Yb/Er) upconversion nanoparticles can be concomitantly incorporated into the epoxy composite, providing an accurate temperature of the composite. The dual functionality should render the epoxy composite an attractive candidate in electronic device.

Plasticity in Crystalline Molecular Explosives – A Key to Unraveling “Unpredictable” Responses

Plasticity in Crystalline Molecular Explosives – A Key to Unraveling “Unpredictable” Responses

The dynamics of unentangled polymers during capillary rise infiltration into a nanoparticle packing.

Although highly packed polymer nanocomposites (PNCs) are important for a wide array of applications, preparing them remains difficult because of the poor dispersion of NPs at high loading fractions. One method to successfully prepare PNCs with high loadings is through capillary rise infiltration, as previously shown by Huang et al., although the mechanism of polymer infiltration remains largely unknown. We use molecular dynamics simulations to directly simulate the process of capillary rise infiltration, and we show that the polymers follow Lucas-Washburn dynamics. We observe a wetting front that precedes bulk infiltration, and chains belonging to this front are highly adsorbed to NPs. We also investigate the viscosity of the model polymers both globally and locally in supported and free-standing films, and we find reduced viscosity near the surface of the films and increased viscosity near the supporting substrate, similar to the results of local relaxation times. The reduction in the viscosity at the free surface for short, oligomeric polymers is smaller than for higher molecular weight polymers, and the ratio of the surface viscosities is most consistent with the predictions of the Lucas-Washburn equation. Our results introduce the mechanism by which polymers infiltrate a highly packed NP film, which may shed light on better ways to prepare these materials for energy storage applications and protective coatings.

Highly Thermal Conductive Copper Nanowire Composites with Ultralow Loading: Toward Applications as Thermal Interface Materials

Thermal interface materials (TIMs) are of ever-rising importance with the development of modern microelectronic devices. However, traditional TIMs exhibit low thermal conductivity even at high loading fractions. The use of high-aspect-ratio material is beneficial to achieve low percolation threshold for nanocomposites. In this work, single crystalline copper nanowires with large aspect ratio were used as filling materials for the first time. A thermal conductivity of 2.46 W/mK was obtained at an ultralow loading fraction, ∼0.9 vol %, which was enhanced by 1350% compared with plain matrix. Such an excellent performance makes copper nanowires attractive fillers for high-performance TIMs.

The effect of carbon nanotube orientation on erosive wear resistance of CNT-epoxy based composites

Aligned carbon nanotube (CNT) polymer composites are envisioned as the next-generation composite materials for a wide range of applications. In this work, we investigate the erosive wear behavior of epoxy matrix composites reinforced with both randomly dispersed and aligned carbon nanotube (CNT) arrays. The aligned CNT composites are prepared in two different configurations, where the sidewalls and ends of nanotubes are exposed to the composite surface. Results have shown that the composite with vertically aligned CNT-arrays exhibits superior erosive wear resistance compared to any of the other types of composites, and the erosion rate reaches a similar performance level to that of carbon steel at 20° impingement angle. The erosive wear mechanism of this type of composite, at various impingement angles, is studied by Scanning Electron Microscopy (SEM). We report that the erosive wear performance shows strong dependence on the alignment geometries of CNTs within the epoxy matrix under identical nanotube loading fractions. Correlations between the eroded surface roughness and the erosion rates of the CNT composites are studied by surface profilometry. This work demonstrates methods to fabricate CNT based polymer composites with high loading fractions of the filler, alignment control of nanotubes and optimized erosive wear properties.

Using Evaporation-Induced Self-Assembly for the Direct Drug Templating of Therapeutic Vectors with High Loading Fractions, Tunable Drug Release, and Controlled Degradation

A novel one-step approach for designing nonaggregated silica-based mesostructured therapeutic vectors is presented. Evaporation-induced self-assembly was used in combination with amphiphilic drugs for preparing already loaded class I and class II hybrid materials containing from 50 to 60 wt % (up to 75 vol %) of three drugs (glucosyl-resveratrol, stearoyl choline, sophorolipid). A good mesostructuration was able to promote an interfacial control of the drug release in PBS medium. The investigation of both release mechanisms and matrix dissolution was conducted via in situ ellipsometry and NMR. It proved that the nature of the drug/matrix interaction, the chemical composition of the drug/matrix interface, and the mesostructuration quality parameters must be taken into account at the same time for tuning the drug release rate, while maintaining the dissolution rate of silica at a reasonable level for limiting its toxicity. It proved also that noncalcined as-made silica-based class I hybrid materials can be ...

Effective in situ material properties of micron-sized SiO2 particles in SiO2 particulate polymer composites

Several analytical models exist for determination of the Young’s modulus and coefficient of thermal expansion (CTE) of particulate composites. However, it is necessary to provide accurate material properties of the particles as input data to such analytical models in order to precisely predict the composite’s properties, particularly at high particle loading fractions. In fact, the constituent’s size scale often presents a technical challenge to accurately measure the particles’ properties such as Young’s modulus or CTE. Moreover, the in situ material properties of particles may not be the same as the corresponding bulk properties when the particles are embedded in a polymer matrix. To have a better understanding of the material properties and provide useful insight and design guidelines for particulate composites, the concept of “effective in situ constituent properties” and an indirect method were employed in this study. This approach allows for the indirect determination of the particle’s in situ material properties by combining the experimentally determined composite and matrix properties and finite element (FE) models for predicting the corresponding composite properties, then backing out the effective in situ particle properties. The proposed approach was demonstrated with micron-size SiO2 particle reinforced epoxy composites over a range of particle loading fractions up to 35vol.% by indirectly determining both the effective Young’s modulus and the effective CTE of the particles. To the best of our knowledge, this study is the first published report on the indirect determination of both the Young’s modulus and the CTE of micron size particles in particulate composites. Similar results on Young’s modulus of micron-size SiO2 particles measured from nano-indentation testing are encouraging.