Shells Of Different Thicknesses Research Articles

Fabrication of hydrogel mini-capsules as carrier systems

Conventional drug administration often results in systemic action, thus needing high dosages and leading to potentially pronounced side effects. Targeted delivery, employing carriers like nanoparticles, aims to release drugs at a target site, but only a small fraction of nanoparticles actually reaches it. Microrobots have been proposed to overcome this issue since they can be guided to hard-to-reach sites and locally deliver payloads. To enhance their functionality, we propose microrobots made as deformable capsules with hydrogel shells and aqueous cores, having the potential added advantages of biocompatibility, permeability, and stimulus-responsiveness. In this study, we present a cost-effective method for fabricating core-shell structures without the use of organic solvents or surfactants. The process begins with the dripping of a mixture of hydrogels, agarose and alginate, into a solution to gelate the drops into beads. After they are loaded with calcium ions at different concentrations, they are immersed in an alginate solution to form the shell. Finally, the beads are heated to let the agarose melt and diffuse out, leaving a liquid core. By varying the concentration of calcium ions, we obtain shells of different thickness. To estimate it, we have developed a method using the colour intensity from microscope images. This allowed us to observe that lowering the calcium ions concentration below a threshold does not lead to the formation of continuous shells. For higher concentrations, although the core may remain partially gelled, continuous shells successfully form. Therefore, our fabrication process could find applications in drug delivery, encapsulation systems, and microrobotics.

Importance of the Structural and Physicochemical Properties of Silica Nanoshells in the Photothermal Effect of Silica-Coated Au Nanoparticles Suspensions.

In this work, monodisperse silica-coated gold nanoparticles (NPs) were synthesized and used for obtaining aqueous colloidal dispersions with an optimum relationship between colloidal stability and photothermal activity. The idea behind this design was to produce systems with the advantages of the presence of a silica shell (biocompatibility, potential for surface modification, and protecting effect) with a minimal loss of optical and thermal properties. With this aim, the photothermal properties of NPs with silica shells of different thicknesses were analyzed under conditions of high radiation extinction. By using amorphous, gel-like silica coatings, thicknesses higher than 40 nm could be obtained without an important loss of the light absorption capacity of the colloids and with a significant photothermal response even at low NP concentrations. The effects produced by changes in the solvent and in the NP concentration were also analyzed. The results show that the characteristics of the shell control both, the photothermal effect and the optical properties of the colloidal dispersions. As the presence of a silica shell strongly enhances the possibilities of adding cargo molecules or probes, these colloids can be considered of high interest for biomedical therapies, sensing applications, remote actuation, and other technological applications.

Investigating metal‐enhanced fluorescence effect on fluorescein by gold nanotriangles and nanocubes using time‐resolved fluorescence spectroscopy

AbstractGold nanotriangles (AuNTs) and nanocubes (NCs) coated with silica shell and fluorescein were synthesized to study the effects of metal‐enhanced fluorescence. The interaction between gold nanoparticles (GNPs) and fluorescein with silica shells of different thicknesses as spacers was investigated by using time‐resolved fluorescence spectroscopy. From the biexponential decay of fluorescence of fluorophore and the kinetic mechanism for the interaction, we obtained the rate constants of energy transfer processes. Both energy transfer rates from fluorophore to the bright and dark modes of gold nanoparticles decreased with distance d (= silica thickness) with a dependence ∝ d−n and n ≈ 2. The rate constant of nanosurface energy transfer kNEST, considering dipolar interaction between fluorophore and metal surface, has an estimated value 1.7 times slower at d = 9 nm and about four times slower at 25 nm than the obtained rate constant for energy transfer from fluorophore to GNP dipolar mode in the AuNT system. For the AuNC system, the rate constants are greater than the AuNT system because of better spectral overlap between emission of fluorescein and surface plasmon resonance.

Investigating the metal-enhanced fluorescence on fluorescein by silica core-shell gold nanoparticles using time-resolved fluorescence spectroscopy

Fluorescein silica core–shell nanoparticles, gold@silica@fluorescein were synthesized to study the effects of metal-enhanced fluorescence (MEF) on fluorescein in neutral and basic ethanol solutions. The interaction between gold nanoparticles and fluorescein with silica shells of different thicknesses as spacers was investigated by time-resolved fluorescence spectroscopy. Only the emission spectra of fluorescein overlapped with the surface plasmon resonance of gold nanoparticles, which is regarded as an example for the study of the emission-enhancement of MEF. The fluorescence spectra of GNP@silica@FiTC were red-shifted from those of silica@FiTC and FiTC in solution. And, the emission curves had biexponential decay, indicating multiple pathways for relaxation of the excited fluorophore. The values of fluorescence enhancement factor (EF) were slightly greater in neutral ethanol solution than in basic solution. The lowest silica shell thickness synthesized, ≈12 nm, had the largest fluorescence EF ≈ 2; this enhancement decreased as the shell thickness increased. At thickness 12 nm, the lifetime of the short component in the emission decay was 60–70 ps and its amplitude close to 90%. Based on the obtained lifetimes, ratios of component amplitudes, and proposed kinetic model, the rate constants for the process of the energy transfer between fluorophores and gold nanoparticles were attained. These rate constants for energy transfer displayed a dependence on the thickness of the silica shell, d-n, where n = 1.3–2.6.

Assessing the protective effects of different surface coatings on NaYF4:Yb3+, Er3+ upconverting nanoparticles in buffer and DMEM

We studied the dissolution behavior of β NaYF4:Yb(20%), Er(2%) UCNP of two different sizes in biologically relevant media i.e., water (neutral pH), phosphate buffered saline (PBS), and Dulbecco’s modified Eagle medium (DMEM) at different temperatures and particle concentrations. Special emphasis was dedicated to assess the influence of different surface functionalizations, particularly the potential of mesoporous and microporous silica shells of different thicknesses for UCNP stabilization and protection. Dissolution was quantified electrochemically using a fluoride ion selective electrode (ISE) and by inductively coupled plasma optical emission spectrometry (ICP OES). In addition, dissolution was monitored fluorometrically. These experiments revealed that a thick microporous silica shell drastically decreased dissolution. Our results also underline the critical influence of the chemical composition of the aqueous environment on UCNP dissolution. In DMEM, we observed the formation of a layer of adsorbed molecules on the UCNP surface that protected the UCNP from dissolution and enhanced their fluorescence. Examination of this layer by X-ray photoelectron spectroscopy (XPS) and mass spectrometry (MS) suggested that mainly phenylalanine, lysine, and glucose are adsorbed from DMEM. These findings should be considered in the future for cellular toxicity studies with UCNP and other nanoparticles and the design of new biocompatible surface coatings.

FTDT simulations of local plasmonic fields for theranostic core-shell gold-based nanoparticles.

The paper describes the results of finite-difference time-domain (FDTD) mathematical modeling of electromagnetic fields distortion near the surfaces of core-shell gold-based spherical gold nanoparticles (NPs). NPs were consistently functionalized by two shells of different thickness: a water shell, as a model substance for a drug, and an SiO2 shell, as a capsuling layer. The calculated field values were converted into the electromagnetic field enhancement coefficient and the surface-enhanced Raman scattering (SERS) intensity. Prospects of the theoretical approach for core-shell NPs modeling to evaluate optimal field amplification and light-scattering parameters have been shown. The presented approach could be applied as a basis for performing methods of controlled synthesis for colloidal core-shell theranostic NPs.

V&V analyses of the GEANT4 Monte Carlo code toolkit with computational and experimental fusion neutronics benchmarks

Verification and Validation (V&V) analyses of the Monte Carlo code toolkit GEANT4 were conducted with nuclear data from the ENDF/B-VII.0 and the JEFF-3.1 library to show the suitability for fusion applications. Two computational benchmarks, a differential and an integral one, and an experimental benchmark were analyzed with GEANT4.10.3 in comparison with MCNP5-1.6. The average relative deviation between GEANT4 and MCNP in the differential benchmark is <1% throughout the energy spectrum for all isotopes and libraries. For the integral benchmark, the deviation of the total neutron flux averaged over a large volume is <1% for all isotopes and libraries with larger deviations in individual energy groups. For the experimental benchmark on iron shells of different thicknesses taken from the SINBAD compilation, the Calculation/Experiment ratios are acceptable for most of the energy spectra with some larger deviations in the range of 4–10.5 MeV. In summary, the results of the V&V analyses indicate the suitability of GEANT4 for the application to fusion neutronics problems.

Effect of Passivating Shells on the Chemistry and Electrode Properties of LiMn2O4 Nanocrystal Heterostructures.

Building a stable chemical environment at the cathode/electrolyte interface is directly linked to the durability of Li-ion batteries with high energy density. Recently, colloidal chemistry methods have enabled the design of core-shell nanocrystals of Li1+ xMn2- xO4, an important battery cathode, with passivating shells rich in Al3+ through a colloidal synthetic route. These heterostructures combine the presence of redox-inactive ions on the surface to minimize undesired reactions, with the coverage of each individual particle in an epitaxial manner. Although they improve electrode performance, the exact chemistry and structure of the shell as well as the precise effect of the ratio between the shell and the active core remain to be elucidated. Correlation of these parameters to electrode properties would serve to tailor the heterostructure design toward complete shutdown of undesired reactions. These knowledge gaps are the target of this study. Li1+ xMn2- xO4 nanocrystals with Al3+-rich shells of different thicknesses were synthesized. Multimodal characterization comprehensively revealed the elemental distribution, electronic state, and crystallinity in the heterostructures, which confirmed the potential of this approach to finely tune passivating layers. All of the modified nanocrystals improved the capacity retention while retaining charge storage compared to the bare counterpart, even under harsh conditions.

Analysis of Stretching of Elastoplastic Samples and Necking with Edge Effects

Large deformations of elastoplastic cylindrical rods and shells of different thicknesses under tension are studied. The effect of sample geometry and the dependence of stresses on deformations under uniaxial tension on edge effects and necking are estimated. The applicability of the Considere criterion for determining the instance of stability loss of plastic tensile strain is analyzed. The computational experiments confirm that the role of similarity in the processes of nonuniform tensile strain of samples can be played by the ratio of the tangent of the slope of the true strain diagram to the stress intensity.

The effect of water absorption on the dielectric properties of polyethylene hexagonal boron nitride nanocomposites

The effect of water absorption on the dielectric response of polyethylene/hexagonal boron nitride nanocomposites has been studied by dielectric spectroscopy. The nanocomposites have been prepared with hBN concentrations ranging from 2 wt% to 30 wt%. Fourier transform infrared spectroscopy and thermogravimetric analysis revealed a very small amount of hydroxyl groups on the surface of hBN. Mass loss measurements showed that the nanocomposites did not absorb any water under ambient and dry conditions while there was some water absorption under wet conditions. The dielectric spectroscopy results showed a broad relaxation peak, indicative of different states of water with water shells of different thickness, which moved to higher frequencies with increasing water content. However, the dielectric losses were significantly lower than the losses reported in the literature of nanocomposites under wet conditions. In addition, all the absorbed water was successfully removed under vacuum conditions which demonstrated that the interactions between the water and the nanocomposites were very weak, due to the hydrophobic nature of the hBN surface. This is a highly useful property, when considering these materials for applications in electrical insulation.

Dual emission and optical gain in PbS/CdS nanocrystals: Role of shell volume and of core/shell interface

Colloidal semiconductor nanocrystals (NCs) emitting simultaneously at two distinct wavelengths are of great interest for multiple applications ranging from ultrasensitive self-calibrating nanoscale sensing to light-emitting diodes and white-light emission. The physical mechanism governing dual emission in core/shell NCs composed of two materials is still under investigation; in particular, the roles of the volume of the shell and of the core/shell interface are not well understood. Here we compare three different PbS/CdS NCs with identical cores, but shells of different thicknesses and different core/shell interfaces. We study photoluminescence (PL) characteristics and ultrafast exciton dynamics with subpicosecond time resolution. We find that dual emission is possible for both thick and thin quantum-confined shells, and for different core/shell interfaces. We show that very thick shells allow the decoupling of shell excitons from core ones and we fully describe the dynamic exciton barrier, connected to efficient shell PL. We discuss the efficiency of shell PL in relation to the properties of the NCs and show that it can give rise to optical gain. Our results provide a comprehensive understanding of the physical phenomena governing dual-emission mechanisms in NCs.

Feasibility of Shell Models for Determining Stress–Strain State and Creep Damage of Cylindrical Shells

The stress–strain state and creep damage of cylindrical shells under internal pressure are studied. The problem solutions for shells of different thickness based on the rectilinear element and the Kirchhoff-Love hypotheses are compared with the three-dimensional solutions for an axisymmetrically loaded hollow cylinder. The effect of the aspect ratio on the accuracy of shell solutions is studied. Practical recommendations for using shell models in creep-damage engineering analysis of cylindrical shells are proposed.

Physico-chemical characteristics, biocompatibility, and MRI applicability of novel monodisperse PEG-modified magnetic Fe3O4&amp;SiO2core–shell nanoparticles

Biocompatible monodisperse PEG-modified magnetic Fe3O4&amp;SiO2core–shell nanoparticles with controlled size provided sufficient contrast for magnetic resonance imaging (MRI).

Cage-like MnO2-Mn2O3 hollow spheres with high specific capacitance and high rate capability as supercapacitor material

This study presents the preparation of novel cage-like MnO2-Mn2O3 particles that have high surface area and macro-porosity. Carbonaceous (C) spheres were first prepared hydrothermally as templates for a subsequent hydrothermal step of MnO2 shell precipitation. Adjusting the Mn precursor concentration and hydrothermal dwell time resulted in MnO2 shells of different thickness. Following calcination to remove carbon, thinner shells resulted in cage-like structure and a higher degree of Mn2O3 content, while thicker shells produced complete hollow spheres. The cage-like MnO2-Mn2O3 hollow spheres (CMHS) produced a 30% larger specific capacity than that of complete hollow spheres at 0.05Ag−1. On a 100 fold current density increase to 5Ag−1 CMHS had a 49.9% of its initial specific capacitance, and had 77.4% capacitance retention after 2000 cycles at 2Ag−1. Cage-like particles, through their high surface area and macro-porosity, thus afford a promising target structure for supercapacitor materials, and can be prepared as described herein.

Fourier Monte Carlo renormalization-group approach to crystalline membranes

The computation of the critical exponent η characterizing the universal elastic behavior of crystalline membranes in the flat phase continues to represent challenges to theorists as well as computer simulators that manifest themselves in a considerable spread of numerical results for η published in the literature. We present additional insight into this problem that results from combining Wilson's momentum shell renormalization-group method with the power of modern computer simulations based on the Fourier Monte Carlo algorithm. After discussing the ideas and difficulties underlying this combined scheme, we present a calculation of the renormalization-group flow of the effective two-dimensional Young modulus for momentum shells of different thickness. Extrapolation to infinite shell thickness allows us to produce results in reasonable agreement with those obtained by functional renormalization group or by Fourier Monte Carlo simulations in combination with finite-size scaling. Moreover, our method allows us to obtain a decent estimate for the value of the Wegner exponent ω that determines the leading correction to scaling, which in turn allows us to refine our numerical estimate for η previously obtained from precise finite-size scaling data.

TiO2@Silica nanoparticles in a random laser: Strong relationship of silica shell thickness on scattering medium properties and random laser performance

A TiO2@Silica nanoparticle has been introduced in a random laser. TiO2 particles with an average diameter of 0.41 μm were coated with silica shells of different thicknesses. Strong dependency of silica shell thickness on the medium scattering strength was found. A mathematical relationship between the scattering mean free path, random laser threshold, and random laser efficiency was developed. Higher efficiency, lower laser threshold, narrower bandwidth, and longest photobleaching lifetime were obtained in the random laser that had increased silica shell thickness. Optical colloidal stability and light coupling enhancement with scattering particles, provided by silica shell, should lead to improved laser performance.

Application of Acoustic Bessel Beams for Handling of Hollow Porous Spheres

Acoustic manipulation of porous spherical shells, widely used as drug delivery carriers and magnetic resonance imaging contrast agents, is investigated analytically. The technique used for this purpose is based on the application of high-order Bessel beams as a single-beam acoustic manipulation device, by which particles lying on the axis of the beam can be pulled toward the beam source. The exerted acoustic radiation force is calculated using the standard partial-wave series method, and the wave propagation within the porous media is modeled using Biot's theory of poro-elasticity. Numerical simulations are performed for porous aluminum and silica shells of different thickness and porosity. Results indicate that manipulation of low-porosity shells is possible using Bessel beams with large conical angles, over a number of broadband frequency ranges, whereas manipulation of highly porous shells can occur over both narrowband and broadband frequency domains.

Dielectric properties of silver nanoparticles coated with silica shells of different thicknesses

Core/shell nanoparticles having metallic silver nanoparticle cores of ∼38 nm in diameter and silica shells of different thicknesses ranging from ∼3.6–20 nm were prepared. For the silica coating, a slightly modified Stober method was used which allowed preparing grams of core/shell nanoparticles for the first time. The particles were characterized by UV-vis spectroscopy, dynamic light scattering, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray scattering. Their dielectric properties were measured as pellets in parallel-plate capacitors. It was found that the permittivity is much influenced by the silica shell thickness with an increase in permittivity for thinner shells. A shell thickness of 20 ± 2 nm allowed fabrication of capacitors which have similar characteristics to those of silica, thus, there is no influence of the metal core on the dielectric properties anymore. However, by decreasing the silica shell to 17 ± 2, 8 ± 1.5, and 6.6 ± 1.5 nm the permittivity at high frequencies is increasing from 10, 34, to 41, respectively. The insulator to metal transition was observed for a silica shell thickness of 3.6 ± 1 nm. Functionalization of the silica surface with a hydrophobic coating removes surface adsorbed water as observed by the flat dielectric permittivity over a large frequency domain.

Practical calculations for uniform external pressure buckling in cylindrical shells with stepped walls

Metal cylindrical storage structures of significant size, such as silos and vertical-axis tanks, are almost always constructed from many short cylindrical shells of different thickness as the stress resultants on the wall progressively increase towards the base. The resulting increases in thickness are always made in step changes using metal sheets of uniform thickness because of the availability of such source materials. The result is a shell with a stepped wall with multiple discrete steps in thickness. Such shells are very susceptible to buckling under external pressure when empty or partially filled, but the buckling mode may involve only part of the shell height due to the changes in shell thickness. These changes must therefore be accounted for within the design process. A new method of determining the critical buckling resistance of such shells was recently developed, and although it has been shown to be valid, the methodology for its application in practical design has not been set out or shown. This paper therefore briefly describes the new method and demonstrates the manner in which it can be used to produce rapid, safe assessments of cylindrical shells with a wide range of patterns of wall thickness changes. The results are then suitable for direct introduction into such documents as the European standard on metal shells [1] and the ECCS Recommendations [2].

Ionothermal synthesis and lithium storage performance of core/shell structured amorphous@crystalline Ni–P nanoparticles

A new strategy for synthesizing Ni–P alloy nanoparticles with a core-shell structure is proposed, which involves a facile ionothermal process in a deep eutectic solvent (DES). The architecture of the core-shell structured Ni–P alloys is featured as amorphous spherical cores homogeneously wrapped by self-generated crystalline Ni3P shells of different thickness, which rely on the molar ratio of Ni2+/H2PO2− in the choline chloride (ChCl)/ethylene glycol (EG) based eutectic mixture. As an anode for lithium ion batteries, cyclic voltammetry curves, electrochemical impedance spectra, and cyclability of the novel structured Ni–P nanoparticles were evaluated. It was found that the sample with a thicker crystalline shell exhibited improved capability and reversibility over the sample with a thinner one, especially at a higher discharge–charge current density. It was suggested that the crystalline shell can enhance the conductivity of the amorphous cores, suppress the aggregation of active particles and increase the structural stability during cycling.