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Dielectric spectroscopy is employed to study the relaxation phenomena in natural polyhydroxyalkanoates (PHAs) upon temperature and frequency variations. Effects of PHAs molecular structure on the relaxation, arising from the differences in monomeric composition, are investigated under identical conditions in a frequency range of 10−2–106 Hz, and at different temperatures. All PHA samples showed different dielectric response at different temperature. Primary α -relaxation signals are observed at temperature corresponding to the glass transition temperature. On the other hand, secondary β - and γ -relaxations are detected at low temperatures, and attributed to local motions of polar groups and small segments of the polymer chain. The dielectric properties of representative PHA samples are compared and discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Azo-esters comprising of 2-methylbutoxy group attached to the terminal azo phenyl. • The lateral methyl and terminal substituents affect mesomorphism of the azo-esters. • Enantiotropic nematic mesophase was observed in the mesogenic compounds. • Optical investigations show all the mesogenic compounds exhibit fluorescent nature. • The laterally methyl-substituted derivatives exhibit antiferroelectric switching. The effect of introducing a lateral methyl substituent and the two different alkoxy terminal groups on the mesophase behavior of three-benzene-ring molecular core of azo-ester compounds bearing 2-methylbutoxy unit on the opposite terminal side (C1 – C6) were explored. Their structures were confirmed by several spectroscopic techniques (Fourier transform infrared spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopy). The mesomorphic properties of these compounds were studied by differential scanning calorimetry, polarized optical microscopy, and small- and wide-angle X-ray scattering. Except for the un-substituted terminals (C1 and C4), all other derivatives are liquid crystalline, exhibiting enantiotropic nematic liquid crystal phase. The alteration of the alkoxy chain length from methoxy to butoxy at the phenyl ester terminal group (ring A) for each set of laterally-neat and laterally methyl-substituted mesogens decreases the nematic temperature range. A decrease in the mesophase temperature range is also observed when a lateral methyl substituent is incorporated into phenylazo ring of the mesogenic core (ring C). Optical study demonstrated that their absorption spectra are identical in shape due to the structural similarities of the mesogenic core. The corresponding fluorescence spectra exhibited blue-emission with the laterally methyl substituted compounds having a relatively higher fluorescence intensity compared to that of its laterally un-substituted analogues. Furthermore, the laterally methyl-substituted derivatives were subjected to the planar alignment and their dielectric and electro-optic properties were investigated. The nematic phase of the aligned samples shows antiferroelectric switching behavior with spontaneous polarization, P s ~ 5 μC/cm2. [ABSTRACT FROM AUTHOR]