Thermal and Dielectric Investigations of Polystyrene Nanoparticles as a Viable Platform—Toward the Next Generation of Fillers for Nanocomposites

Abstract

Nanoparticles are often used as fillers for enhancing various properties of polymer composites such as mechanical, electrical, or dielectric. Among them, polymer nanoparticles are considered ideal contenders because of their compatibility with a polymer matrix. For this reason, it is important that they are synthesized in a surfactant-free form, to obtain predictable surface and structural properties. Here, we synthesized a series of polystyrene nanoparticles (PS NPs), by emulsion polymerization of styrene, using varying amounts of divinylbenzene as a crosslinking agent and sodium 4-vinylbenzenesulfonate as a copolymerizing monomer surfactant—“surfmer”. Using “surfmers” we obtained surfactant-free nanoparticles that are monodisperse, with a high degree of thermal stability, as observed by scanning electron microscopy and thermogravimetric investigations. The prepared series of NPs were investigated by means of broadband dielectric spectroscopy and we demonstrate that by fine-tuning their chemical composition, fine changes in their dielectric and thermal properties are obtained. Further, we demonstrate that the physical transformations in the nanoparticles, such as the glass transition, can be predicted by performing the first derivative of dielectric permittivity for all investigated samples. The glass transition temperature of PS NPs appears to be inversely correlated with the dielectric permittivity and the average diameter of NPs.

Effect of Asymmetric Lobe Size on the Molecular Dynamics, Glass Transition, and Dielectric Behavior in Janus Nanoparticles

“…Before examining the temperature dependences of ε′, we need to notice that the thermogravimetric measurements as well as representative differential scanning calorimetry thermograms for homologous series of seed PS NPs and JNPs NPs were extensively discussed in our previous studies. , All the seed NPs and the corresponding JNPs exhibited a high thermal stability with the degradation process starting around 400 °C. , Moreover, the glass transition temperature ( T g ) of nonpolar seed NPs was found between 113 and 116 °C, depending on the synthesis conditions. On the other hand, the T g of the polar PTSPM component cannot be determined because it is a highly cross-linked polymer.…”

“…30 At the same time, the "ring modes" of benzene originating from the aromatic C�C bonds are detected at 1598 and 1492 cm −1 . 22,32 Furthermore, the transmittance band centered around 1449 cm −1 may be attributed to aliphatic C−C bonds, whereas the intensive infrared bands observed in the low-frequency region between 800 and 500 cm −1 correspond to aromatic C−H out-of-plane bending of the phenyl ring. 22,30,31 The supplementary transmittance bands with reduced intensity at wavenumbers of 1184 and 1025 cm −1 correspond to asymmetric and, respectively, symmetric modes of the S−O stretching vibration.…”

“…22,32 Furthermore, the transmittance band centered around 1449 cm −1 may be attributed to aliphatic C−C bonds, whereas the intensive infrared bands observed in the low-frequency region between 800 and 500 cm −1 correspond to aromatic C−H out-of-plane bending of the phenyl ring. 22,30,31 The supplementary transmittance bands with reduced intensity at wavenumbers of 1184 and 1025 cm −1 correspond to asymmetric and, respectively, symmetric modes of the S−O stretching vibration. 33 The latter indicates the presence of functional SO3 − groups originating from the NaVBS "surfmer" in the seed PS NPs.…”

“…38 The numerical value of ε′ (at 0.1 Hz) is 2.5, which is comparable to other PS NPs with permittivity values between 2.5 and 2.9. 22,39,40 After the addition of the PTSPM lobe, the ε′ behavior of JNPs changed considerably. First, the ε′ magnitude of snowman JNPs is higher than that of seed PS NPs, revealing a superior dipolar activity for JNPs.…”

“…22,41 All the seed NPs and the corresponding JNPs exhibited a high thermal stability with the degradation process starting around 400 °C. 22,41 Moreover, the glass transition temperature (T g ) of nonpolar seed NPs was found between 113 and 116 °C, depending on the synthesis conditions. On the other hand, the T g of the polar PTSPM component cannot be determined because it is a highly cross-linked polymer.…”