Nanoscale Effect Investigation for Effective Bulk Modulus of Particulate Polymer Nanocomposites Using Micromechanical Framework

This paper investigates the nanoscale effect on the effective bulk modulus of nanoparticle-reinforced polymer. An interface-based model is introduced in this work to study the nanoscale effects on the effective properties of heterogeneous materials. That interface model is able to capture discontinuity of mechanical fields across the surface between the nanoparticle and matrix. A generalized self-consistent scheme is then employed to determine the effective bulk modulus. It has been seen from the results that, in a certain range of limits, the influence of nanoscale effects on effective properties of heterogeneous materials is significant and needs to be taken into account. In particular, when the nanoparticle radius is smaller than 10 nm, the value of effective bulk modulus significantly increases when the characteristic size of nanofillers decreases. Besides, it is seen that the harder the inclusion, the smaller the nanoscale influence effects on the overall behaviors of composite materials. Finally, parametric studies in terms of surface strength and filler’s volume fractions are investigated and discussed, together with a comparison between the proposed model and other contributions in the literature.

Анализ оптических свойств однородных металлических, окисных наночастиц и двухслойных наночастиц с металлическим ядром и окисной оболочкой с целью эффективного поглощения солнечной радиации

Problems related to using nanoparticles for absorption of solar radiation and photothermal nanotechnologies are now being actively studied. The efficiency of using nanoparticles as photothermal agents for solar energy is determined by their spectral optical properties. We performed computer simulation of optical properties of homogeneous metal (nickel, titanium, and molybdenum) nanoparticles and their oxides, along with nanoparticles consisting of a metal core and an oxide shell, with radii in the range from 50 to 100 nm in the spectral interval between 200 and 2500 nm. The influence of nanoparticle radius, the type of metal and its oxide on spectral coefficients of efficiency absorption ( K _abs) and scattering ( K _sca) of radiation by nanoparticles is investigated. The type of nanoparticles suitable for absorption of solar radiation was chosen based on a comparative analysis of the wavelength dependences of absorption efficiency coefficients K _abs, intensity of solar radiation I _ S , and parameter P _1 = K _abs/ K _sca. Spherical double–layer nanoparticles consisting of nickel or titanium core and oxide shells with a radius of 75 or 100 nm can be used in the spectral interval from 200 to 2500 nm for efficient absorption of solar radiation. These results are a substantial contribution to the investigation of optical properties of nanoparticles that can be used in systems of thermal energy.

Modeling spectral properties of transparent matrix composites containing core-shell nanoparticles

Optical properties of transparent matrix composites containing metal nanoparticles coated with an oxide shell were numerically simulated based on the Aden-Kerker theory applicable for concentric spheres. Using pentaerythritol tetranitrate composites (containing Al/Al2O3 nanoparticles) as an example, the linear scattering and absorption coefficients as well as the total reflectance and transmittance and collimated beam transmittance were shown to be determined by the sample thickness, the nanoparticle radius, the mass fraction of nanoparticles, and mass fraction of the oxide in the nanoparticles. An approach to determining the said parameters based on the comparison of the calculated spectral dependencies of the reflectance and transmittance with the experimental ones was suggested. The nanoparticle radius was determined with the minimum error (of about 2 – 3 %), while the nanoparticle mass fraction and oxide mass fraction were weak parameters determined with a 25 % error.

Determination of the melting and freezing temperatures of Pb nanoparticles embedded in a PbO–B2O3–SnO2glass by using only the SAXS method

Melting and freezing of metallic nanoparticles embedded in glass matrices usually occur at temperatures lower than for the same metal in the bulk state.In situsmall-angle X-ray scattering (SAXS) measurements using a synchrotron beamline and a specially designed high-temperature chamber allowed the determination of the temperature dependence of the SAXS intensity produced by a dilute and nearly monodisperse set of spherical Pb nanoparticles, with an average radius 〈R〉 = 16.1 nm, embedded in a homogeneous lead–borate oxide glass. The temperature dependences of the nanoparticle volumeV(T) and nanoparticle radius of gyrationRg(T) derived from SAXS results exhibit clear discontinuities during the cooling and during the heating processes, thus allowing for precise determinations of the melting and freezing temperatures of the studied Pb nanoparticles. Additional features observed in bothV(T) andRg(T) curves showed that during the heating cycle the frozen Pb nanoparticles suffer a transition to a more compact phase at 433 K before melting at 580 K. The results of this work demonstrate that the melting and freezing temperatures of nanoparticles in a very diluted state – for which the X-ray diffraction technique is not sensitive enough – can be precisely determined by applying only the SAXS method.

Structure, dynamics and primitive path network of polymer nanocomposites containing spherical nanoparticles

ABSTRACTWe investigate the effect of nanoparticles on polymer structure, polymer dimensions and topological constraints (entanglements) in polymer melts for nanoparticle loading above percolation threshold as high as 40.9% using stochastic molecular dynamics (MD) simulations. We show unambiguously that short polymer chains are not disturbed by the presence of repulsive nanoparticles. In contrast entangled polymer chains can be perturbed by the presence of attractive nanoparticles when the polymer radius of gyration is larger than the nanoparticle radius. They can expand under the presence of attractive nanoparticles even at low nanoparticle loadings of very small nanoparticle size. We observe an increase in the number of entanglements (decrease of Ne with 40.9% volume fraction of nanoparticles dispersed in the polymer matrix) in the nanocomposites as evidenced by larger contour lengths of the primitive paths. Attraction between polymers and nanoparticles affects the entanglements in the nanocomposites and alters the primitive path.

RADIAL VIBRATION CHARACTERISTICS OF SPHERICAL NANOPARTICLES IMMERSED IN FLUID MEDIUM

The vibrational properties of nanoparticles coupled with surrounding media are of recent interest. These nanostructures can be modeled as nanoscale spherical solids. In this paper, new formulation based on the nonlocal elasticity theory is proposed to investigate radial vibrations of the nanoparticles immersed in fluid medium. The nanoparticles with size ranging from 1 nm to 10 nm are discussed. The nanoparticles are considered elastic, homogeneous and anisotropic. Along the contact surface between the nanoparticle and the fluid, the compatibility requirement is applied and the Bessel functions are used to obtain the complex frequency equation. Numerical results are evaluated, and their comparisons are performed to confirm the validity and accuracy of the proposed method. Furthermore, the model is used to elucidate the effect of small scale on the vibration of several nanoparticles. Our results show that the small scale is essential for the radial vibration of nanoparticles when the nanoparticle radius is smaller than 2 nm.

OPTICAL AND STRUCTURAL PROPERTIES OF Ag NANOPARTICLES Eu OXIDE FILMS

Silver-incorporated europium oxide thin films have been prepared by the successive evaporation method on quartz and silicon substrates. The silver concentration was 2.5% and 8.9% respectively, as measured by X-ray fluorescence. X-ray diffraction revealed that the Eu oxide of these samples remained amorphous after preannealing at 450°C; however, it crystallized in bcc structure at 800°C. The lattice parameter of the crystallized Eu oxide was larger than that of the bulk, due to the adsorption of Ag + ions, which have a higher ionic radius. The optical absorption of the samples manifested the surface plasmon resonance (SPR) phenomenon, which varied with the Ag content and preannealings of the samples at different temperatures. The Ag nanoparticle radius was estimated with the Mie classical theory by using the SPR data analysis.

The Effect of Nanoparticles on the Thermal Conductivity of Crystalline Thin Films at Low Temperatures

This study is concerned with the prediction of the effective thermal conductivity of nanocomposite thin films consisting of nanoparticles randomly distributed in a solid matrix. Crystalline sodium chloride with embedded monodisperse silver nanoparticles is investigated as a case study for thin films where phonons are the main heat carriers. To the best of our knowledge, the equation for phonon radiative transfer is solved for the first time with an exact scattering transport cross-section of the nanoparticles as a function of frequency which was obtained from the literature. The one-dimensional equation for phonon radiative transfer based on the isotropic scaling approximation is solved on a spectral basis using the discrete ordinates method to predict the temperature profile and the heat flux across the nanocomposite thin films. The thermal conductivity is retrieved at temperatures where the effects of Umklapp and Normal processes can be neglected and scattering by the particles on phonon transport dominates. The method of solution and closure laws were validated with experimental data of thermal conductivity for bulk samples at 2.53, 5.94, and 10.56 K. The effects of the film thickness (1 μm to 2.5 cm), nanoparticle diameter (5 nm to 100 nm) and volume fraction (0.0001 to 0.2) on the thermal conductivity of the nanocomposite thin film are investigated. The results indicate that the thermal conductivity decreases with decreasing particle radius as well as with increasing particle concentration. Finally, a dimensionless analysis revealed a power law relationship between the dimensionless thermal conductivity and a dimensionless length of the order of the acoustic thickness of the medium. These results can be used to design nanocomposite thin films for various low temperature thermal applications by choosing optimal nanoparticle radius and volume fraction, and film thickness.