Thermal transitions and molecular dynamics in main‐chain liquid crystalline polyester/fullerene nanocomposites

Abstract

Molecular dynamics and liquid crystalline (LC) transitions in nanocomposites with main‐chain liquid crystalline alkylene–aromatic polyester as a matrix and fullerene C60 as a filler, with filler content varying from 0.3 up to 5 wt% were studied. Measurements by differential scanning calorimetry (DSC) and temperature modulated DSC techniques were performed in order to study glass transition and LC transitions. Dielectric relaxation spectroscopy (DRS) was used both to record LC transitions through isochronal measurements at four different frequencies during cooling/heating at constant rate and to study molecular mobility through isothermal measurements in a wide temperature and frequency range, −150°C to 190°C and 10−1 to 106 Hz, respectively. Glass transition and LC transitions were followed for the neat matrix as well as for the nanocomposites. A moderate increase of glass transition temperature in nanocomposites was found, while the LC transitions were shifted to lower temperatures with increasing filler content. A good correlation between DSC and DRS results was found. For all the samples under study four dielectric relaxations were followed by DRS, in order of increasing temperature: two secondary relaxations, β and γ, the α‐relaxation related to the amorphous phase glass transition and an interfacial relaxation (Maxwell–Wagner–Sillars, MWS) due to charge accumulation at the amorphous–crystalline interface. The experimental data were analyzed in detail and the results revealed rather weak effects of fullerenes on molecular dynamics. POLYM. COMPOS., 38:E331–E341, 2017. © 2016 Society of Plastics Engineers