Synthesis,characterization and conducting properties of novel poly (vinyl cinnamate)/zinc oxide nanocomposites via in situ polymerization

New polymer nanocomposite based on poly (vinyl cinnamate) (PVCin) with zinc oxide (ZnO) was synthesized by in situ polymerization of vinyl cinnamate with different concentrations of ZnO nanoparticles. The composite was characterized through FT-IR, FT-Raman, UV spectroscopy, XRD, HRTEM, FE-SEM, DSC, TGA and electrical conductivity studies. The IR, Raman and UV spectra ascertained the structural variation of PVCin network by the insertion of nanoparticles within the polymer segment. The morphological studies by TEM and FE-SEM photographs indicate that the nanopowder was uniformly dispersed in the polymer. The presence of nanoparticles in the nanocomposite was clearly observed from the XRD studies and the ordered arrangement of nanoparticles within the macromolecular chain of PVCin increased with increase in concentration of nanofillers. DSC results showed that the glass transition temperature and crystalline melting point were increased smoothly with the increase in concentration of nanoparticles. Analysis of TGA studies showed a significant increase in thermal stability with an increase in weight percentage of nanoparticles. The DC conductivity of nanocomposite was increased by ten orders of magnitude with the addition of 7 wt% of nano ZnO inclusion. AC conductivity, dielectric constant and dielectric loss tangent of nanocomposite was remarkably increased with increase in ZnO content up to 7 wt% of filler particles. Both AC and DC conductivity and dielectric properties were decreased beyond 7 wt% loading.     

Photochemical Formation of Au/Cu Bimetallic Nanoparticles with Different Shapes and Sizes in a Poly(vinyl alcohol) Film

Metal nanoparticle (NP)–polymer nanocomposite thin films are attractive for applications in various devices. Since bimetallic NPs provide additional opportunities for tuning the physical properties of the NP components, the development of bimetallic NP nanocomposite thin films should lead to further enhancements of various applications. Au/Cu bimetallic NPs are fabricated in a poly(vinyl alcohol) (PVA) film using a photochemical process. Interestingly, different sizes and shapes of Au/Cu bimetallic NPs are formed in the PVA film, resulting in a uniquely patterned nanocomposite structure. It is determined that the different formation and growth mechanisms of NPs inside and outside the UV‐light irradiation spot leads to the differences in size and shape.     

Processing,device fabrication and electrical characterization of LaMnO3 nanofibers

Lanthanum manganite (LaMnO₃) nanofibers were synthesized using electrospinning technique. The size and uniformity of these nanofibers were optimized by varying PVP concentration. X-ray diffraction analysis revealed the formation of single phase LaMnO₃ nanofibers (average diameter ~400 nm) when the composite nanofibers were calcined at 600 °C. M″ and Z″ spectroscopic plots of impedance spectroscopy data confirmed the presence of two distinct electro-active regions referred to as the grain and grain boundary regions. The activation energies of the grain and grain boundary regions were 0.27 eV and 0.41 eV, respectively; which suggested two different transport mechanisms in these fibers.     

A Novel Cross‐linked Poly(vinyl alcohol) (PVA) for Vascular Grafts

Poly(vinyl alcohol) (PVA) is a water‐soluble synthetic polymer with excellent film‐forming, emulsifying, and adhesive properties. The aim of this study is to design a simple process for PVA cross‐linking with sodium trimetaphosphate to form membrane devices suitable for biomedical applications. This procedure requires no organic solvent, nor melting process to obtain films with high mechanical strength. Fabrication of a small diameter tube from a PVA film is easy with a single wrapping step around a Teflon rod. Dynamic mechanical analysis demonstrated that, upon removal of the applied stress, the PVA film with a Young's modulus of 2 × 10⁵ kPa returns to its original size and shape. The wall thickness of PVA tubes is 344 ± 13 µm (n = 12), which is close to the wall thickness of a human artery (350–710 µm). Suture retention of a PVA tube is excellent (140 ± 11 g), close to that of human vessels. The burst pressure of PVA tubes is found to be 507 ± 25 mm Hg, more than three times higher than the human healthy systolic arterial pressure. Under arterial pressure, there was no leakage even after needle puncture, contrary to clinical vascular expanded polytetrafluoroethylene prostheses. Finally, PVA tubes of 2 mm in diameter are used to replace a segment of an infrarenal aorta in rats. For at least one week, no mechanical nor thrombotic complications are noticed even in the absence of anticoagulant or antiplatelet treatment. Graft patency is also evidenced with non‐invasive imaging techniques. As a conclusion, this novel cross‐linking method confers to poly(vinyl alcohol) particular mechanical properties such as compliance, elasticity and resistance to mechanical stress, compatible with the circulatory blood flow.     

Synthesis and characterizations of poly(3,6-thienophenanthrene) and poly(2,7-thienophenanthrene) and their applications in polymer light-emitting devices and solar cells

Here we report the synthesis of two novel phenylene-based polymers-poly(3,6-thienophenanthrene) (PTP36) and poly(2,7-thienophenanthrene) (PTP27) via base-free Suzuki–Miyaura reaction. The structure and electroluminescent properties of the meta-linked PTP36 and para-linked PTP27 are fully characterized. The obtained polymers were found to be liquid-crystalline, with broad band gap of 2.72 eV and 2.49 eV, respectively, which are much smaller than those of corresponding polyphenanthrenes. On the basis of PTP36 and PTP27, copolymers of 2,7-thienophenanthrene and 3,6-thienophenanthrene with 5,6-bis(octyloxy)-4,7-di(thiophen-2-yl)benzothiadiazole (DBT), namely PTP36-DBT and PTP27-DBT were prepared and be investigated as a potential donor material for polymer solar cells. The preliminary data show that the maximal power conversion efficiencies (PCEs) of the PTP27-DBT- and PTP36-DBT-based polymer solar cells are 3.5% and 0.9%, respectively.     

Synthesis and characterization of lead selenide nanostructure through simple sonochemical method in the presence of novel precursor

In the present study, PbSe nanostructures have been synthesized by using [bis(salicylate)lead(II)]; [Pb(Hsal)₂] as lead precursor in the presence of sonochemical method in aqueous solution. Besides, the effects of reaction time, ultrasonic power, and surfactant on the morphology and particle size of products were studied by SEM images. It was found out that the size and morphology of the products were greatly influenced by these parameters. The XRD studies indicated the production of pure cubic PbSe nanostructures could only happen in the presence of ultrasonic radiation. The average diameter of the PbSe nanostructures was 12 nm. Products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL) and EDX analysis.     

Patterned Color and Fluorescent Images with Polydiacetylene Supramolecules Embedded in Poly(vinyl alcohol) Films

Poly(vinyl alcohol) (PVA) films embedded with functional polydiacetylene (PDA) are efficiently prepared for color and fluorescence imaging. Intensely blue films are obtained by mixing and drying solutions containing PDA vesicles and PVA. A blue‐to‐red color transition is observed upon heating the polymer films. In addition, selective UV irradiation (through a photomask) of PVA films containing diacetylene monomer results in the generation of micropatterned color (without heating) and both color and fluorescent images (after heating the films at 120 °C for 10 s). Patterned two‐color (blue and red) images in the polymer film are readily obtained by a sequential process of photomasked irradiation, heating, and unmasked irradiation.     

Poly(vinyl alcohol) Rehydratable Photonic Crystal Sensor Materials

We developed a new photonic crystal hydrogel material based on the biocompatible polymer poly (vinyl alcohol) (PVA), which can be reversibly dehydrated and rehydrated, without the use of additional fillers, while retaining the diffraction and swelling properties of polymerized crystalline colloidal arrays (PCCA). This chemically modified PVA hydrogel photonic crystal efficiently diffracts light from the embedded crystalline colloidal array. This diffraction optically reports on volume changes occurring in the hydrogel by shifts in the wavelength of the diffracted light. We fabricated a pH sensor, which demonstrates a 350 nm wavelength shift between pH values of 3.3 and 8.5. We have also fabricated a Pb⁺² sensor, in which pendant crown ether groups bind lead ions. Immobilization of the ions within the hydrogel increases the osmotic pressure due to the formation of a Donnan potential, swelling the hydrogel and shifting the observed diffraction in proportion to the concentration of bound ions. The sensing responses of rehydrated PVA pH and Pb⁺² sensors were similar to that before drying. This reversibility of rehydration enables storage of these hydrogel photonic crystal sensors in the dry state, which makes them much more useful for commercial applications.     

The interplay of electronic structure,molecular orientation and charge transport in organic semiconductors: Poly(thiophene) and poly(bithiophene)

Ultrathin films of poly(thiophene) (PT) and poly(bithiophene) (PBT) were prepared by electrochemical route using ionic liquid (BFEE) as medium and electrolyte. Distinct morphologies and electrical properties were observed in these materials. To evaluate its response in photovoltaics, these films were used as active layer in bilayer geometry solar cells with the electron acceptor molecule C₆₀. The best performance was observed for PT films. In order to probe the differences in molecular dynamics and structural order, ultrafast electron dynamics in the low-femtosecond regime was evaluated by resonant Auger spectroscopy using the core–hole clock method at the sulfur K absorption edge. Electron delocalization times for the different polymeric films were derived as a function of the excitation energy. Photoabsorption measurements were conducted and molecular orientation derived. These results corroborated with the morphology found for these films and thus the performance of PT and PBT in the devices, and with the proposed conduction mechanism.     

Poly(vinyl alcohol) Scaffolds with Tailored Morphologies for Drug Delivery and Controlled Release

Poly(vinyl alcohol) (PVA) scaffolds are prepared by a cryogenic process that consists of the unidirectional freezing of a PVA solution. The scaffolds exhibit a microchanneled structure, the morphology of which (in terms of pore diameter, surface area, and thickness of matter accumulated between adjacent microchannels) can be finely tailored by the averaged molecular weight of PVA, the PVA concentration in the solution, and the freezing rate of the PVA solution. The resulting PVA scaffolds are suitable substrates for drug‐delivery purposes, the drug release being controlled (from tens of minutes up to several days) by the morphology of the microchanneled structure. In vitro experiments reveal the efficiency of PVA scaffolds for controlling the release of ciprofloxacin into a bacteria culture medium.     

Electrical characterization of poly(amide-imide) for application in organic field effect devices

The admittance spectra and current–voltage (I–V) characteristics are reported of metal–insulator–metal (MIM) and metal–insulator–semiconductor (MIS) capacitors employing cross-linked poly(amide–imide) (c-PAI) as the insulator and poly(3-hexylthiophene) (P3HT) as the active semiconductor. The capacitance of the MIM devices are constant in the frequency range from 10 Hz to 100 kHz, with tan δ values as low as 7 × 10⁻³ over most of the range. Except at the lowest voltages, the I–V characteristics are well-described by the Schottky equation for thermal emission of electrons from the electrodes into the insulator. The admittance spectra of the MIS devices displayed a classic Maxwell–Wagner frequency response from which the transverse bulk hole mobility was estimated to be ∼2 × 10⁻⁵ cm² V⁻¹s⁻¹ or ∼5 × 10⁻⁸ cm² V⁻¹s⁻¹ depending on whether or not the surface of the insulator had been treated with hexamethyldisilazane (HMDS) prior to deposition of the P3HT. From the maximum loss observed in admittance-voltage plots, the interface trap density was estimated to be ∼5 × 10¹⁰ cm⁻² eV⁻¹ or ∼9 × 10¹⁰ cm⁻² eV⁻¹ again depending whether or not the insulator was treated with HMDS. We conclude, therefore, that HMDS plays a useful role in promoting order in the P3HT film as well as reducing the density of interface trap states. Although interposing the P3HT layer between the insulator and the gold electrode degrades the insulating properties of the c-PAI, nevertheless, they remain sufficiently good for use in organic electronic devices.     

High performance top-gate field-effect transistors based on poly(3-alkylthiophenes) with different alkyl chain lengths

The device characteristics of top-gate field-effect transistors (FETs) based on typical polymer semiconductor regioregular poly(3-alkylthiophenes) (P3ATs) with different alkyl chain lengths are investigated. High field-effect mobilities of ∼10⁻² cm²/Vs are obtained irrespective of alkyl chain length even when polymer gate insulators with different dielectric constants (2.1–3.9) are used. This is attributed to the spontaneous formation of highly ordered edge-on lamellar structures at the surface of P3AT thin films that are the channel regions in top-gate FETs. In addition, top-gate P3AT FETs containing different gate insulators exhibit high operational stability, with low threshold voltage shifts of <0.5 V following prolonged gate bias stress, which is comparable to that of hydrogenated amorphous silicon thin film transistors.     

Effect of solution aging on morphology and electrical characteristics of regioregular P3HT FETs fabricated by spin coating and spray coating

The paper reports on a comparative study of poly(3-hexylthiophene) (P3HT) films as well as P3HT organic field effect transistors (OFETs) fabricated by the spin coating and spray coating techniques, using fresh and aged (for 2 months) chloroform solutions. The films obtained from aged solutions contain nanostructured fibers of the polymer. The presence of nanofibers in P3HT thin films affects the performance of the OFETs: charge carrier mobilities in the samples deposited from the aged solutions appeared over one order of magnitude higher than those fabricated using fresh solutions. Particularly high mobilities, exceeding 10⁻² cm² V⁻¹ s⁻¹, were found in spin coated samples deposited from aged solutions. Additionally, the latter samples exhibit a certain degree of anisotropy, associated with the action of centrifugal force during the deposition.     

Polarized photoluminescence and electroluminescence in oriented films of regioregular poly(3-alkylthiophenes)

We report polarized photoluminescence (PL) and electroluminescence (EL) from regioregular poly(3-alkylthiophene) thin films oriented by means of the rubbing technique. With a proper thermal annealing of the rubbed films we have increased the anisotropy reaching values up to 8 both in PL and EL. We have evidenced that the orientation in the rubbing direction is higher for the longest conjugation segments than for the less conjugated ones. Moreover polarized PL study demonstrates that emission takes place after migration of the excitation from shorter, less oriented, to longer, more oriented conjugation segments.     

New triphenylamine-based poly(amine-imide)s with carbazole-substituents for electrochromic applications

A new carbazole-derived triphenylamine-containing diimide-diacid monomer (5), 4,4′-bis(trimellitimido)-4″-N-carbazolytriphenylamine, is prepared by the condensation of 4,4′-diamino-4″-N-carbazolytriphenylamine (4) and two molar equivalents of trimellitic anhydride (TMA). A series of new poly(amide-imide)s (PAIs) 7a–7d with carbazole-substituted triphenylamine units are prepared by direct polymerization from the new diimide-diacid (5) and various aromatic diamines (6a–6d). The PAIs shows high glass transition temperature between 269 and 297 °C, and high 5% weight loss temperature between 526 and 561 °C under nitrogen environment. Cyclic voltammograms of the PAIs films, which are casted onto the indium–tin oxide (ITO)-coated glass substrate, exhibit two reversible oxidation redox couples at 1.05–1.08 V and 1.38–1.46 V under an anodic sweep. The PAI-7a film reveals excellent stability of electrochromic characteristics for the radical cations generated, changing color from original pale yellowish neutral form to the green and then to dark blue oxidized forms. Furthermore, the anodically coloring of PAI-7a shows high coloration efficiency (CE = 205 cm²/C), high contrast of optical transmittance change (ΔT = 80% at 776 nm) and long-term redox reversibility.     

A new multicolored and near-infrared electrochromic material based on triphenylamine-containing poly(3,4-dithienylpyrrole)

A new compound containing both 3,4-dithienylpyrrole (DTP) and triphenylamine (TPA) groups, namely, 4′-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)-N,N-diphenylbiphenyl-4-amine (DTP-Ph-TPA), was designed and synthesized. The polymer poly-DTP-Ph-TPA (PDTP-Ph-TPA) was prepared by electropolymerization from DTP-Ph-TPA. When the applied potential circulates from 0.0 V to 1.4 V, the polymer not only exhibits reversible multicolor in the visible region (yellow, light green, magenta and blue), but also shows excellent electrochromic properties in the NIR region with high contrast ratio (ΔT = 70.5% in 1550 nm, ΔT = 67.9% in 1310 nm) and a very short response time (about 1.4 s for 1550 nm, 0.9 s for 1310 nm). A single layer electrochromic device (ECD) based on polymer PDTP-Ph-TPA was constructed and characterized.     

Nanoscale photovoltaic characteristics of single quantum dot hybridized with poly(3-hexylthiophene)

Hybrids consisting of CdSe/ZnS quantum dot (QD) as a core and thiol-group functionalized poly(3-hexylthiophene) (P3HT) as a shell were fabricated using the ligand-exchange method. We clearly observed the photovoltaic characteristics of a single QD-P3HT hybrid by using conducting atomic force microscopy. Monochromatic power conversion efficiency drastically increased with an increase in the molecular weight (Mw) of P3HT, suggesting sufficient photoinduced charge transfer between the QD and highly ordered P3HT chains. The nanoscale photoluminescence (PL) intensity for a single QD considerably decreased with increasing Mw of P3HT owing to charge transfer effects. On the basis of time-resolved PL and transient absorption spectra measurements of the QD-P3HT hybrids, we deduced that the exciton lifetimes of the QD were reduced with higher-Mw P3HT hybrids, and photobleaching was observed. The measured nanoscale optical characteristics of the single QD-P3HT hybrids support their distinct photovoltaic behaviors.     

Synthesis and characterization of poly (linoleic acid)-g-poly(methyl methacrylate) graft copolymer with applying in Au/PLiMMA/n-Si diode

Poly (linoleic acid)-g-poly(methyl methacrylate) (PLiMMA) graft copolymer was synthesized and characterized. PLiMMA graft copolymer was synthesized from polymeric linoleic acid peroxide (PLina) possessing peroxide groups in the main chain by free radical polymerization of methyl methacrylate. Later, PLiMMA was characterized by proton nuclear magnetic resonance (¹H NMR), gel permeation chromatography (GPC), thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques. Furthermore, Au/PLiMMA/n-Si diode was fabricated for the purpose of investigating PLiMMA׳s conformity in diodes. The main electrical characteristics of this diode were investigated using experimental current–voltage (I–V) measurements in dark and at room temperature. Obtained results, such as sufficiently high rectifying ratio of 4.5×10⁴, indicate that PLiMMA is a promising organic material for electronic device applications.     

Molecular weight and processing effects on the dissolution properties of thin poly(methyl methacrylate) films

An experimental set-up based on multiwavelength interferometry, is applied in order to study in-situ the dissolution process of thin resist films. The interference function was the basis for a fitting algorithm, which analyses the experimental data and evaluates the progress of the resist thickness with time. The dissolution of various PMMA molecular weights (15 K, 350 K, 996 K) and resist thicknesses (20-300 nm), in various developers, consisting of mixtures of methyl iso butyl ketone (MIBK), iso propanol (IPA), H₂O at various relative concentrations, was studied. Surface dissolution inhibition was shown in unexposed resists with high molecular weights and increased thickness in the case of MIBK-IPA 1-1 and IPA-H₂O 7-3 developers. After that the whole dissolution process evolved at a steady rate. Dissolution of thick films proved to be unpredictable showing complex dissolution curves. Low molecular weight resists presented a smooth dissolution curve without dissolution inhibition. Samples exposed with small DUV doses, exhibited dissolution behavior similar to the unexposed cases, whereas high exposure doses, within the lithographically useful range, led to smooth dissolution behavior. In the case of MIBK-IPA 1-3 developer significant swelling was observed.     

Effects of fullerene solubility on the crystallization of poly(3-hexylthiophene) and performance of photovoltaic devices

The substantial crystallization suppression of poly(3-hexylthiophene) (P3HT) in the untreated P3HT:C60 composite film prepared from o-dichlorobenzene (ODCB) solution has been revealed. Besides, the effective conjugation length of P3HT in this composite has been nearly maintained to that in the solution. The different crystallization behaviors of P3HT in its composites with C60 and [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) are mainly attributed to the relative solubility of C60 and PCBM with respect to P3HT in ODCB. The solution to overcome this disadvantage of chain conformation and crystallinity of P3HT in the composite with C60 is thus proposed and finalized by resorting to the addition of low volatile solvent with much higher solubility of C60 than P3HT into the main solvent used, so as P3HT can crystallize before C60 forms crystallites in the solution. The feasibility of this approach has been proven by the improved efficiency of devices based on composites of P3HT and the low cost C60 without resorting to post-treatments. Our results demonstrated in this study could further benefit development of new electron acceptor materials, particularly based on fullerenes and their derivatives, by considering the role of the new materials in determining the crystallization of the other components involved in the composite film.