Research of Size- and Shape-Dependent Thermodynamic Properties of the Actual Melting Process of Nanoparticles

Abstract

Melting phase transitions of nanoparticles are often involved in the preparations, research studies, and applications of nanomaterials. However, because of the changing melting temperature of nanoparticles during the melting process, the current relations of melting thermodynamic properties fail to accurately describe their actual melting behaviors. In this study, accurate thermodynamic relations between integral melting enthalpy and entropy and the size of nanoparticles with different shapes (sphere, rod, wire, and regular polyhedrons) were derived for the first time through designing a thermochemical cycle. In the experiment, Ag nanospheres, nanowires, and nanocubes with different sizes were prepared by chemical reduction methods, and differential scanning calorimetry was employed to determine the melting temperature, the melting enthalpy and the melting entropy. The experimental results agree with the theoretical predictions, indicating that the melting thermodynamic properties decrease with the particle size decrease and present linear variations with the inverse particle size within the experimental size range. Moreover, the melting enthalpy and entropy of nanoparticles in identical equivalent diameters take the same sequence as that of melting temperature as T o (wire) > T o (sphere) > T o (cube). The derived relations of melting thermodynamic properties can quantitatively describe the actual melting behaviors of nanoparticles, and the findings herein provide us a comprehensive understanding of the melting thermodynamic properties of nanomaterials in the whole melting process.

Plasmon‐Enhanced Blue Upconversion Luminescence by Indium Nanocrystals

“…XRD data of InNCs did not show any characteristic Bragg peaks because of the room temperature melting phenomenon, which implies that the prepared InNCs consist of molten In droplets (Figure c). This observation also agrees well with previous studies that melting of In nanoparticle happens near room temperature if its diameter is below 10 nm . Comparison of the UV–vis absorption spectra of InNCs, NaYbF 4 :Tm nanoparticles, and NaYbF 4 :Tm@SiO 2 @In nanocomposites in Figure d, indicates that InNCs and NaYbF 4 :Tm@SiO 2 @In nanocomposites have strong absorption at 265 and 270 nm, respectively, which suggests the presence of InNCs in the nanocomposites.…”

Overview of Synthetic Methods to Prepare Plasmonic Transition‐Metal Nitride Nanoparticles

“…Furthermore, nanoscale metals exhibit low melting temperatures,w hich make such materialsu ndesirable for devices operating at high temperatures. [17,18] Non-noble metals, such as Al, Cu, Ga, In, Sn, Mg, and Ni, have been explored, but oxidative degradation can lead to weakening of the LSPRs demonstrated by these materials. [19][20][21][22] As ar esult, there has been ag reat effort to find alternative cost-effective plasmonic materials that demonstrate high chemical and thermals tability in addition to an effective plasmonic response.…”

Size‐Dependence of the Melting Temperature of Individual Au Nanoparticles

“…[17] Several thermodynamic models were developed to describe the melting temperature of nanoparticles, such as the Pawlow model, [18] the Rie model, [19] and the model proposed by Reiss and Wilson. [20] The melting temperature dependence on particle size was also discussed by Fu et al, [21][22] Xue et al [23] and Cui et al [24] However these models typically fail to predict the melting temperature of smaller nanoparticles (d < 5 nm), due to the introduction of approximations in their derivation. [4] This study applies a combined experimental and computational approach to investigate the melting properties of Au nanoparticles as a function of particle size.…”