W.H. Abd. Majid

SONOCHEMICAL SYNTHESIS OF HIERARCHICAL ZNO NANOSTRUCTURES

This work is about fabrication of ZnO nanostructures (ZnO-NS) via a simple sonochemical method. The chemicals used for the synthesis of various shaped ZnO are Zn salt, sodium hydroxide and ammonia solution without other structure directing agent or surfactant needed. This method is feasible and green, as it does not require high temperature and/or highly toxic chemicals. The shape of the ZnO-NS can be tuned by adjusting the ultrasound energy dissipated via varying the ultrasonication time from 5 to 60 min. It was found that uniform ZnO nanorods with diameter around 50 nm were formed after 15 min of ultrasonication while flowerlike ZnO-NS was formed after 30 min. This method produces high quality ZnO-NS with controllable shapes, uniformity, and purity.

Synthesis and characterization of a narrow size distribution of zinc oxide nanoparticles

Zinc oxide nanoparticles (ZnO-NPs) were synthesized via a solvothermal method in triethanolamine (TEA) media. TEA was utilized as a polymer agent to terminate the growth of ZnO-NPs. The ZnO-NPs were characterized by a number of techniques, including X-ray diffraction analysis, transition electron microscopy, and field emission electron microscopy. The ZnO-NPs prepared by the solvothermal process at 150°C for 18 hours exhibited a hexagonal (wurtzite) structure, with a crystalline size of 33 ± 2 nm, and particle size of 48 ± 7 nm. The results confirm that TEA is a suitable polymer agent to prepare homogenous ZnO-NPs.

Hot Plate Annealing at a Low Temperature of a Thin Ferroelectric P(VDF-TrFE) Film with an Improved Crystalline Structure for Sensors and Actuators

Ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer 70/30 thin films are prepared by spin coating. The crystalline structure of these films is investigated by varying the annealing temperature from the ferroelectric phase to the paraelectric phase. A hot plate was used to produce a direct and an efficient annealing effect on the thin film. The dielectric, ferroelectric and pyroelectric properties of the P(VDF-TrFE) thin films are measured as a function of different annealing temperatures (80 to 140 °C). It was found that an annealing temperature of 100 °C (slightly above the Curie temperature, Tc) has induced a highly crystalline β phase with a rod-like crystal structure, as examined by X-ray. Such a crystal structure yields a high remanent polarization, Pr = 94 mC/m2, and pyroelectric constant, p = 24 μC/m2K. A higher annealing temperature exhibits an elongated needle-like crystal domain, resulting in a decrease in the crystalline structure and the functional electrical properties. This study revealed that highly crystalline P(VDF-TrFE) thin films could be induced at 100 °C by annealing the thin film with a simple and cheap method.

Theoretical and experimental approach on dielectric properties of ZnO nanoparticles and polyurethane/ZnO nanocomposites

ZnO nanoparticles (ZnO-NPs) were synthesized by a new, simple sol-gel method in gelatin media (particle size of ZnO ≈ 30 to 60 nm). Polyurethane/ZnO nanocomposites thin films (PU/ZnO-NPs) were prepared by mixing the ZnO-NPs into PU prepolymer. The nanocomposites were structurally characterized using Fourier transmission infrared (FTIR) spectroscopy. The interaction between ZnO-NPs and PU matrix is studied by analyzing the differences in C=O region and N-H region of FTIR spectra. The morphology of ZnO and PU/ZnO nanocomposites were assessed using transmission electron micrograph, TEM, and field emission scanning electron microscope, FESEM, respectively. The dielectric properties of ZnO-NPs were attributed to the interfacial and orientation polarization. Measurement is reported for the real and imaginary parts of the ac conductivity of ZnO-NPs in the frequency range of 10 to 106 Hz in the temperature range 298–478 K. The experimental results are interpreted in terms of the classical correlated-barrier hoppi...

Pyroelectricity enhancement of PVDF nanocomposite thin films doped with ZnO nanoparticles

A thin film of pyroelectric composite with 0–3 connectivity was fabricated from zinc oxide (ZnO) nanopowder and polyvinylidene fluoride (PVDF) with different volume fraction from 0–0.25 wt%. The dielectric and pyroelectric properties of the samples were investigated. It was found that the presence of a small amount of ZnO nanoparticles (0.25 wt%) has significantly increased the pyroelectric coefficient of the PVDF by 25%. Furthermore, the nanocomposite films required lower poling field to form polar-δ phase compared to pure PVDF thin films. Analysis of the complex permittivity in a wide range of frequency was carried out indicating that the dielectric constant and loss of PVDF/ZnO nanocomposite thin films increase when doped with ZnO. Havriliak-Negami (HN) empirical function has been employed to obtain the αrelaxation time of the nanocomposite thin films before and after poling. The α-relaxation time does not vary with the increase of ZnO wt%; however, the effect of poling has lengthened the relaxation time of the thin films. FTIR and XRD results supports the fact that the addition of ZnO nanoparticles into PVDF polymer thin films do not cause any significant effect on the structure of the PVDF thin films. In fact, ZnO nanoparticle has enhanced the overall pyroelectricity of PVDF by facilitating the poling process in the composites and led to phase transformation of PVDF from α -t oδ-phase as supported by a marked reduction of (100) x-ray diffraction intensities.

Study and fabrication of europium picrate triethylene glycol complex

A mononuclear of [Eu(NO3)(Pic)(H2O)2(EO3)](Pic)·(0.73)H2O complex, where EO3=trietraethylene glycol and Pic=picrate anion, shows a red emission when used as an active layer in a single layer of ITO/EO3-Eu-Pic/Al configuration. The crystal structure of the complex consists of [Eu(NO3)(Pic)(H2O)2(EO3)]+ cation and [Pic]- anion. The Eu(III) ion is coordinated to the 10 oxygen atoms from one EO3 ligand, one Pic anion, one nitrate anion, and two water molecules. The complex is crystallized in triclinic with space group P-1. The hybrids in thin films I and II were prepared in the respective order solution concentrations of 15 and 20 mg/mL the emissive center. Comparing the photoluminescence (PL) and electroluminescence (EL) spectra, we can find that all emissions come from the characteristic transitions of the Eu(III) ion. The EL spectra of both thin films showed the occurrence of the most intense red-light emission around at 612 nm. Comparison of organic light-emitting device (OLED) current intensity characteristics as a function of voltage (I-V) show that the thin film I is better than those found for the thin film II. The thickness of the emitting layer is an important factor to control the current-voltage curve. The sharp and intense emission of the complex at low voltage indicates that the complex is a suitable and promising candidate for red-emitting materials.

Qualitative evaluation of pyroelectric mechanisms in Langmuir–Blodgett films containing a cyclic polysiloxane substituted with aliphatic side chains using Fourier transform infrared (FTIR) spectroscopy

Abstract Alternate layer Langmuir–Blodgett (LB) films containing cyclic polysiloxane substituted with aliphatic side chains alternated with monomeric eicosylamine have been shown to exhibit pyroelectric activity. The pyroelectric activity for 5, 11, 15, 21, 25 and 31 monolayer LB films, is recorded at 21°C and shows highest activity for 5 monolayers with a pyroelectric coefficient of 0.5 μC m −2 K −1 . The coefficient decreases as the thickness of the film increases from 5 to 15 monolayers, increases in the thickness range of 15–25 monolayers and decreases again for 31 monolayers film. Fourier transform infrared (FTIR) spectroscopy shows that proton transfer between the acid headgroups at the terminal end of the cyclic polysiloxane and the headgroups of the eicosylamine increases as the number of monolayer increases. However, the angle at which the molecular axis of the LB film tilts from the surface normal, α (as indicated by the overall ratio of symmetric stretching of CH 2 to CH 3 , or asymmetric stretching of CH 2 to CH 3 ) increases as the number of monolayer increases from 5 to 15 layers and remains stable for 21–31 layers.

Piezoelectric and pyroelectric properties of BNT-base ternary lead-free ceramic–polymer nanocomposites under different poling conditions

Lead-free 0.88(Na0.5Bi0.5) TiO3–0.084(K0.5Bi0.5) TiO3–0.063BaTiO3 (BNT–BKT–BT) piezoelectric ceramic powders were incorporated into a polyvinylidene fluoride-trifluoroethylene [P(VDF-TrFE)] copolymer matrix to form 0–3 composites. Composites with BNT–BKT–BT volume fraction O ranging from 0.10 to 0.40 were fabricated using a hot-press method. These compositions were poled using various procedures to produce three types of samples: one with only the ceramic phase poled; one with polymer and ceramic phases poled in the same direction; and one with the polymer and ceramic phases poled in opposite directions. The effect of the polarisation state on the piezoelectric coefficient d33 and pyroelectric coefficient p of the composite was investigated as a function of the ceramic volume fraction O. For the purpose of steadying and compensating the polarization domain, extra free charges were added by the presence of BNT–BKT–BT. In the sample with both ceramic and polymer phases poled in the same direction, the pyroelectric coefficient increased from 26 to 95 μC m−2 K−1 when the ceramic volume fraction increased from 0–0.20; this is greater than that of the P(VDF-TrFE)-PZT 0–3 composites. In the sample with the phases of the composite film polarised in opposite directions, their piezoelectric activities were reinforced, and d33 was found to increase from 28 to 40 (pC N−1) with a change in ceramic volume fraction ranging between 0 and 30%. One promising usage of the enhanced pyroelectric composites with the ceramic phase and the copolymer phase poled in the same direction is that of sensing components within pyroelectric sensors, while integration in ultrasonic transducer applications is possible in the case of the enhanced piezoelectric composites with the ceramic phase and the copolymer phase poled in opposite directions.

Phase sensitive molecular dynamics of self-assembly glycolipid thin films: A dielectric spectroscopy investigation

Glycolipid, found commonly in membranes, is also a liquid crystal material which can self-assemble without the presence of a solvent. Here, the dielectric and conductivity properties of three synthetic glycolipid thin films in different thermotropic liquid crystal phases were investigated over a frequency and temperature range of (10(-2)-10(6) Hz) and (303-463 K), respectively. The observed relaxation processes distinguish between the different phases (smectic A, columnar/hexagonal, and bicontinuous cubic Q) and the glycolipid molecular structures. Large dielectric responses were observed in the columnar and bicontinuous cubic phases of the longer branched alkyl chain glycolipids. Glycolipids with the shortest branched alkyl chain experience the most restricted self-assembly dynamic process over the broad temperature range studied compared to the longer ones. A high frequency dielectric absorption (Process I) was observed in all samples. This is related to the dynamics of the hydrogen bond network from the sugar group. An additional low-frequency mechanism (Process II) with a large dielectric strength was observed due to the internal dynamics of the self-assembly organization. Phase sensitive domain heterogeneity in the bicontinuous cubic phase was related to the diffusion of charge carriers. The microscopic features of charge hopping were modelled using the random walk scheme, and two charge carrier hopping lengths were estimated for two glycolipid systems. For Process I, the hopping length is comparable to the hydrogen bond and is related to the dynamics of the hydrogen bond network. Additionally, that for Process II is comparable to the bilayer spacing, hence confirming that this low-frequency mechanism is associated with the internal dynamics within the phase.

Langmuir-Blodgett films of linear polysiloxanes incorporating aromatic side-chains: structure-property relationships

Abstract Four aromatic acid side-chain polymers on two different polysiloxane backbones, namely poly(hydrogen-methylsiloxane) homopolymer and poly(hydrogenmethylsiloxane-dimethylsiloxane) copolymer, have been synthesised and characterised. Two different ω-(4-alkoxyphenyl)alkanoic acid side-groups have been studied whose primary spacer groups (the alkyl chain that separates the siloxane backbone from the oxyphenyl group) are -(CH 2 ) 8 - and -(CH 2 ) 4 - and whose secondary spacer groups (the alkyl chain that separates the oxyphenyl group from the carboxylic acid group) are both -(CH 2 ) 2 -. All of these compounds form stable Langmuir films on a pure water subphase and can be co-deposited with monomeric eicosylamine (CH 3 (CH 2 ) 19 NH 2 ) to form alternate layer ABABA… superlattices. Such assemblies exhibit the pyroelectric effect. Indeed, one such alternate layer LB film containing monolayers of the polysiloxane copolymer backbone substituted with aromatic side-chains has yielded one of the highest quasi-static pyroelectric coefficients ever reported for LB films. Its value of 4.6 microC m −2 K −1 is a factor of 3 greater than the coefficient measured for a similar polysiloxane copolymer/eicosylamine multilayer in which the siloxane backbone is substituted with purely aliphatic acid side-groups. Therefore the presence of a molecular dipole (oxyphenyl) within each side-chain, in addition to the ionic dipole that arises from proton transfer between acid and amine groups in adjacent monolayers, has led to a dramatically improved pyroelectric response.