Temperature dependence of the dielectric permittivity of poly(methyl methacrylate) filled with metal nanoparticles

Abstract

245Our previous investigations of metal-polymer nanocomposites based on high pressure (low density) polyethylene (LDPE) matrix revealed some anomalies in the temperature dependences of the dielectric prop erties of these materials [1]. The existing qualitative models used to describe these properties [2] imply that the generation of carriers in the volume of nanoparti cles accounts for the appearance of polar elements in the polymer matrix.An analogous approach has been used in the present study for analysis of the properties of nano composites based on a poly(methyl methacrylate) (PMMA) matrix containing stabilized silver nanopar ticles. The obtained results are explained based on the assumption that the PMMA matrix is doped with an impurity in the form of stabilized nanoparticles.We have studied the samples of nanocomposites comprising a PMMA matrix filled with stabilized Ag nanoparticles at a concentration within 3-10 mass %. The nanoparticles were stabilized in a polymer melt solution using the method of thermal decomposition of unstable precursor compounds. At the first stage, the composition was obtained in the form of a powder. Then, thermal pressing was used to manufacture sam ple plates with a thickness of about 100 μm and lateral dimensions of 5 × 5 mm. The nanoparticle dimensions and their distribution in the polymer matrix were stud ied by transmission electron microscopy, which showed that the average size of Ag nanoparticles was 10-20 nm and the variance of their normal distribu tion did not exceed 10%. The dielectric function of the nanocomposite was studied using a method analogous to that described previously [1].The nanocomposite materials were studied in a measuring cell of the sandwich type, which was placed into a controlled temperature system for the heating and cooling of samples. The sample was fixed in the cell by copper clamp contacts. The aim of this investi gation was to measure the temperature dependence of the dielectric properties of PMMA based nanocom posites filled with stabilized silver nanoparticles. Another aim was to study the influence of the mass fraction of stabilized nanoparticles on the shape of this temperature dependence and to determine the ColeCole diagrams of nanocomposites at various tempera tures. These measurements were performed at a fre quency of 1 kHz in a temperature interval of 300-380 K in a thermostat linked to an E7 8 digital LCR meter used to record data on the capacitance and con ductance of the samples. The method of capacitance and conductance determination and the numerical calculation of complex dielectric permittivity was analogous to that used previously [1]. All measure ments were performed in air. Figure 1 presents the plot of the relative permittiv ity versus temperature, which shows that heating of the sample is accompanied by an increase in its permittiv ity and the subsequent cooling leads to the formation of a hysteresis. The appearance of the permittivity hys teresis was also observed in LDPE based nanocom posites, where it was explained by...