Evaluation of the (Allyl alcohol 1,2‐butoxylate‐block‐etoxylate)‐b‐PMMA Copolymers Composition by the Dielectric Measurements

Redox initiated free‐radical polymerization of methyl methacrylate (MMA) with allyl alcohol 1,2‐butoxylate‐block‐etoxylate (AABE) was carried out to yield AABE‐b‐PMMA copolymers at elevated temperatures. The composition of the copolymers depending on the polymerization temperature was qualitatively estimated by the dielectric measurements. It has been seen that AABE segment quantity decreased and PMMA segment quantity increased with increasing the polymerization temperature. The dielectric constant and the dissipation factor of the copolymers were investigated as a function of frequency and temperature. The dielectric constant and the dissipation factor were found to be strongly affected by the polymerization temperature. The highest dielectric constant in all studied temperatures and frequencies was obtained in the case of the copolymer which was prepared at 313 K. The dipolar C‐O and OH groups of the AABE segment have the primary effect on the dielectric constant. The copolymer which was prepared at 323 K, showed the highest dissipation factor near the relaxation temperature of PMMA.     

Synthesis,Characterization and Comparison of Properties of Novel Fluorinated Polyimides Derived from Bisphenol–A‐di(phthaleic anhydride)

Four new poly(etherimide)s have been synthesized by reaction with commercially available bisphenol‐A‐(diphthaleic anhydride) (BPADA) with four different kinds of diamines, namely 4,4′‐bis(p‐aminophenoxy‐3,3″‐trifluoromethyl) terphenyl,4,4′‐bis(3″‐trifluoromethyl‐p‐aminobiphenyl ether)biphenyl,2,6‐bis(3′‐trifluoromethyl‐p‐aminobiphenyl ether)pyridine, 2,5‐bis(3′‐trifluoromethyl‐p‐aminobiphenylether)thiopene. The poly(etherimide)s are named as 1a, 1b, 1c and 1d, respectively. The synthesized polyimides show good solubility in various organic solvents. The polyimide films had low water absorption of 0.19–0.30% and low dielectric constant of 2.79–3.1 at 1 MHz. These polyimides showed very high thermal stability with decomposition temperature (5% wt loss) up to 522°C in nitrogen. Transparent thin films of these polyimides exhibited tensile strength up to 97 MPa, a modulus of elasticity up to 1.56 GPa and elongation at break up to 20%.     

Silver Nanoparticles in Polyacrylamide and Hyperbranched Polyamine Matrix

Silver nanoparticles have been prepared in a polyacrylamide (PA) matrix, as well as in the presence of a hyperbranched polyamine/polyacrylamide combined system (HB‐PA) by using a reductive technique. The stability of colloidal solution of silver nanoparticles is higher (5 months) in combined matrix compared to PA alone (4 months). The prepared silver nanoparticles were characterized by different spectroscopic and analytical techniques such as FTIR, UV‐visible, X‐ray diffraction, TEM etc. TEM and XRD studies confirmed the formation of well‐dispersed nanoparticles with an average size of 9.91 nm and 8.5 nm for PA and HB‐PA matrices, respectively. The antibacterial activity of silver nanoparticles in both the matrices was tested against Bacillus Subtilis bacteria by using the diffusion disc technique. The result shows that the antibacterial activity of the active agent, Ag(0) is a little higher in the case of HB‐PA system. The dielectric constant of the matrices decreases with an increase in frequency, but the values increase with an increase of concentration of silver nanoparticles in PA matrix.     

Broadband dielectric characterization of piezoelectric poly(vinylidene fluoride)thin films between 278 K and 308 K

This work describes the dielectric properties of piezoelectric poly(vinylidene fluoride) (PVDF) thin films in the frequency and temperature ranges relevant for usual applications. We measured the isothermal dielectric relaxation spectra of commercial piezoelectric PVDF thin films between 10 Hz to 10 MHz, at several temperatures from 278 K to 308 K. Measurements were made for samples in mechanically free and clamped conditions, in the direction of the poling field (perpendicular to the film). We found that the imaginary part of the dielectric relaxation spectra of free and clamped PVDF samples is dominated by a peak, above 100 kHz, that can be characterized by a Havriliak-Negami function. The characteristic time follows an Arrhenius dependence on temperature. Moreover, the spectra of the free PVDF samples show two additional peaks at low frequencies which are associated with mechanical relaxation processes. Our results are important for the characterization of piezoelectric PVDF, particularly after the stretching and poling processes in thin films, and for the design and characterization of a broad range of ultrasonic transducers.     

Studies on the Effect of Organic Solvents and Temperature on the Micellar Solution of Pentamethylene-1,5-bis(tetradecyldimethylammonium bromide) Gemini Surfactant

Effects of three organic solvents, viz. methyl cellosolve, acetonitrile, and formamide, on the micellization process of Gemini surfactant pentamethylene-1,5-bis(tetradecyldimethylammonium bromide) aqueous solutions, with the volume percentages of the organic solvents up to 50%, have been investigated conductometrically. The studies were made at different temperatures and the data were used to find out different micellization parameters. From the study, it was observed that, although an increment in the amount of the organic solvents delays the micellization, the increase in the critical micelle concentration (cmc) is comparatively less below 20%(v/v) showing the predominance of water character in the bulk phase at lower compositions of the organic solvents. Applying equilibrium model for micelle formation, various thermodynamic parameters were also calculated from the temperature dependence of the cmc values and the results show that the micellization process becomes less spontaneous as the volume % of the organic solvent increases in the system due to the action of water-organic solvent mixed media as better solvent than pure water (solvophobic effect) for the studied Gemini molecules.     

Analysis of Crude Oils by Frequency Domain Spectroscopy—Effect of Composition and Physical Properties on Conductivity and Dielectric Response

The dielectric properties and the composition of fourteen light to heavy crude oils have been analyzed. Frequency domain spectroscopy (FDS) has been used in order to determine their dielectric response in the frequency range 0.01 to 1000 Hz. For all the crude oils, over the whole frequency range under study, dielectric loss, ?″, shows a linear dependence of frequency indicating a pure direct current (DC) conductivity. As temperature is gradually increased, the dielectric loss, ?″, increases as well, showing a strong temperature dependence. The storage modulus, ?′, shows an explicit behaviour at low frequency that could be due to adsorption of oil components onto the electrodes. We tried to correlate some physical and chemical properties (density, viscosity, SARA, TAN, water content) of the studied crude oils with their conductivity measured at various temperatures. No correlation was found and different hypothesis are suggested by the authors to explain this phenomenon.     

The liquid crystal properties of symmetric and non-symmetric dimers based on the azobenzene mesogenic group

A novel system of symmetric and non-symmetric dimers containing azobenzene groups has been synthesized and studied in an attempt to understand further the molecular origins of the intercalated smectic phases. For the non-symmetric dimers, the lack of symmetry was derived solely from the differences in length of the two terminal alkyl chains. Both the spacer and terminal chain lengths were varied. The spacer length was found to exert a profound influence on the clearing temperatures of these materials and a large odd-even effect was observed for the series. The smectic A phase stability was observed to increase with the terminal chain length, yet decrease with increasing spacer length. X-ray diffraction has revealed the structure of the smectic A phase of both the symmetric and non-symmetric azobenzene dimers to be of the monolayer type and not intercalated. The existence of the intercalated phase has previously been explained in terms of either a charge-transfer interaction, or by an electrostatic quadrupolar interaction. However, it has been thought that it may also be the result of an excluded volume or space filling constraint. For the non-symmetric liquid crystal dimers described here, a charge-transfer interaction should be minimal, as should the stabilization from the quadrupolar interaction between the two mesogens. However, it appears that some sort of specific interaction is required to stabilize the intercalated structure.     

Electro-optic effect,propagation loss,and switching speed in polymers containing nano-sized droplets of liquid crystal

Polymers containing droplets of liquid crystal smaller than 100 nm, which have good transparency and easily form films, were prepared under various conditions to evaluate their potential as electro-optic materials for waveguide-type devices. By varying the liquid crystal concentration and the strength of the UV irradiation causing photo-induced phase separation of the droplets, we were able to control the droplet size and density. We have clarified how the birefringence generated in an applied electric field, switching speed, and optical loss of light propagating in the film depend on droplet size and density. Polymer materials having a large electro-optic effect (δn = 0.001 at 8 V μm^-1), low propagation loss (~2.5 dB cm^-1), and fast response time (~10 μs) have been developed.     

Structure and photoconductive behaviour of a sanidic liquid crystal

A series of [1]benzothieno[3,2-b][1]benzothiophene-2,7-dicarboxylate derivatives consisting of a flat, conjugated aromatic moiety containing sulphur hetero-atoms and substituted by terminal chains - ethyl, decyl, Z-4-decenyl or 2-(2-butoxyethoxy)ethyl - has been synthesized. These materials exhibit a smectic liquid crystalline phase, the stability of which was found to be strongly dependent on the length and the nature of the terminal chains. In the mesophase, the molecular arrangement within the smectic layer is characterized by a local stacking of the rigid parts similar to that found in discotic columnar systems. Finally, clear photoconductive behaviour was found in mechanically aligned samples of these liquid crystals.