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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] • Thermotropic phase behaviours of α -D-mannosides containing nonsymmetrical Guerbet branched chains at sub-zero temperatures. • Occurrence of rippled structures implies the competition between hydrophobic volume and headgroup surface packing. • Temperature-dependent changes in the primary relaxation time were investigated through distortion-sensitive analyses. • Shear viscosity test indicates all liquid crystal phases exhibits shear thinning behaviour. Many aspects govern the nature of the resulting phase of a self-assembly of glycolipid, including its detailed stereochemical structure, solvent type, and state condition. Glycolipid has attracted considerable attention due to its extensive lyotropic applications in surfactant industry and material science. However, its application as thermotropic liquid crystal is unknown and rarely investigated. Herein, the thermotropic properties of a series of glycolipids, namely Guerbet branched chain α -D-mannosides (C 8 to C 24 total carbons) were studied by X-ray scattering, dielectric spectroscopy, and rheology. The shortest chain α ManC 6 C 2 exhibited lamellar phase over the entire temperature range whereas both α ManC 8 C 4 and α ManC 10 C 6 only at elevated temperatures since these have larger hydrophobic volumes. Interestingly, at the room temperature, both anhydrous α ManC 8 C 4 and α ManC 10 C 6 showed formation of rippled structures. Prior to transforming into the fluid lamellar phase, these complex structures possess greater viscosity than the former. The longer chain mannosides (α ManC 12 C 8 and α ManC 14 C 10) adopted an inverse bicontinuous Ia 3 d cubic and inverse hexagonal phases, respectively. The temperature-dependent evolution of dielectric relaxation times, τ (T) of primary relaxation within the lamellar, hexagonal, and isotropic phases is explored. Distortion-sensitive tests, enabled by derivative-based analysis, evaluate the suitability of τ (T) parametrisation using the Vogel-Fulcher-Tammann (VFT) and critical-like equations. According to the dielectric and rheological analyses, as the temperature increases, both ε ‖ a n d ε ⊥ increased, while the viscosity decreased. The findings suggest that higher temperatures are accountable for higher molecular mobility and fluidisation of the phase structure. These fundamental investigations are important to the bottom-up approach development of regulated and specially designed nanoscale material (e.g., a cryoprotective agent). [ABSTRACT FROM AUTHOR]

Glycolipids prepared from palm kernel oil, PKO, in tropical regions represent an excellent opportunity to develop new surfactant formulations for cosmeceutical and pharmaceutical applications while contributing to sustainable economies. Here we report the synthesis of a new mannoside obtained from palm kernel oil, aManPKO, and we characterise its thermotropic properties by using DSC, POM, SAXS, WAXS, FT-IR and broadband dielectric spectroscopy. aManPKO exhibits a monotropic smectic phase with a partially interdigitated bilayer structure, similar to its major unsaturated component, the oleyl mannoside with a C18:1 monounsaturated alkyl chain. The smectic phase of aManPKO vitrifies below room temperature, which is associated to the C18:1 component, but also to the activation of short-range motions, ~4 Å, by cleavage of strong hydrogen bonding between the polar heads of the mannosides. The stability of the liquid crystal phase, on the other hand, is linked to the presence of weak hydrogen bonding, whose breakage leads to the activation of long rate motions in the range of the layer distances, ~39 Å. [ABSTRACT FROM AUTHOR]

• Exhaustive photochromic, dielectric and electrochemical analysis of an azobenzene-based organic compound, tAZOi. • tAZOi assembles into molecular dimers by hydrogen-bonding between thymine heads. • An ITO/tAZOi/Al device presents two switchable conductance states with preservation of memory performance. • Conductivity in the transition between ground and excited states is p-type, involving hydrogen-bonded thymine heads. • tAZOi increases dielectric permittivity driven by trans-to-cis isomerisation of the azobenzene groups upon UV irradiation. • Molecular simulations suggest that device performance can be enhanced by light exposure. In the search to obtain new and more efficient components of memory devices, we report the photochromic, dielectric and electrochemical response of a light-responsive organic compound, and its memory performance under electrical fields. The so-called N(1)-[12-(4-(4′-isobutyloxyphenyldiazo)phenoxy)dodecyloxy)]thymine, tAZOi, molecule contains one azobenzene group, which provides with photochromic character, and one terminal thymine group, capable to form hydrogen bonds and assemble supramolecular dimers, (tAZOi) 2. We have calculated the optical absorption coefficient, extinction coefficient and refractive index of tAZOi, which obeys the single oscillator Wemple–DiDomenico model. An ITO/tAZOi/Al device has been prepared and presents two switchable conductance states with preservation of memory performance. The mechanism linked to the resistive random-access memory (RRAM) has been evaluated by molecular modelling and is controlled by p-type conduction, possibly involving hydrogen-bonding. Upon UV irradiation at ∼ 365 nm, tAZOi displays an increase in the complex permittivity driven by trans -to- cis (E -to- Z) isomerisation of the azobenzene groups. Molecular simulations suggest that conductivity and device performance can be enhanced (and controlled) by light exposure through the formation of activated Z isomers that could transfer charge to other neighbouring molecules, resulting in photo-electric responsive devices. [ABSTRACT FROM AUTHOR]