Intercalation of Perylenediimide Dye into LDH Clays: Enhancement of Photostability

Intercalation of perylenediimide dye into a host layer of layered double hydroxide (LDH) by the anion-exchange method is studied N,N'-Bis(4-benzosulfonic acid)-perylene-3,4,9,10-tetracarboxylbisimide disodium salt (PRSA) has been synthesized and intercalated into the perchlorate form of ZnAl-, CoAl-, and NiAl-LDH. LDH composite with well-defined morphology has been prepared. XRPD and FT-IR investigation show successful intercalation of PRSA, and the interlayer distances are 32.5 angstrom for ZnAl-LDH-PRSA, 30.0 angstrom for CoAl-LDH-PRSA, and 31.2 angstrom for NiAl-LDH-PRSA. These values support the presence of monolayer arrangement of intercalated PRSA molecules in the composite and also indicate vertical orientation of PRSA molecules with the basal plane of LDH. Photophysical properties of these intercalated composites have been measured with UV-vis spectroscopy, photoluminescence spectroscopy, and confocal laser scanning microscopy. The results indicate that the PRSA molecules are stacked in J-type aggregation in the interlayer region. Intercalated PRSA molecules show enhanced thermal and photophysical stabilities

Lamination of cationic perylene in montmorillonite nano-gallery: induced J-aggregated nanostructure with enhanced photophysical and thermogravimetric aspect

Intercalation of perylenediimide dye into host layer of native Na-montmorillonite (Na-MMT) by anion exchange method is studied. Three cationic perylene diimides (PMC, PEC, and PBC) with different side chains have been synthesized and intercalated into Na-MMT to produce three composites PM-MMT, PE-MMT, and PB-MMT, respectively. Perylene-MMT composites with well-defined intercalated morphology have been prepared. XRPD and FT-IR and HR-TEM investigations show successful intercalation of cationic perylene and the interlayer distances are 0.74 nm for PM-MMT, 0.84 nm for PE-MMT, and 1.24 nm for PB-MMT. These values support the presence of monolayer arrangement of intercalated perylene dye molecules inclined within MMT nanogalleries. Photophysical properties of these intercalated composites have been measured with UV-vis spectroscopy, photoluminescence spectroscopy, and fluorescence microscopy. The results indicate that the perylene dyes are stacked as J-type aggregation in the interlayer region. Intercalated perylene molecules show enhanced thermal and photophysical stability

Immobilization of poly(fluorene) within clay nanocomposite: An easy way to control keto defect

Blue light emitting cationic polyfluorene polymer(PF)/montmorillonite (MMT) nanocomposites were prepared by solution intercalation and exfoliation method to evaluate the effect of MMT on the nanocomposite structures, properties and morphologies. The properties of PF-MMT composites, containing 1-50 mass% MMT, were characterized unambiguously with the help of multiple analytical techniques, with focus on the keto defect and photostability of PF in the nanocomposites. XRD and HRTEM studies reveal both exfoliation of MMT galleries at lower content of MMT in composites and intercalation of PF chains into the MMT galleries at higher MMT content. The nanocomposites show higher thermal stability than pristine PF as anchorage of nanoclay in PF matrix occur through the electrostatic interaction between nanoclay and polymer. The decrease in Si-O-Si stretching frequency during exfoliation is much higher than in intercalation, as Si-O-Si experience lesser hindrance to vibrate in exfoliated MMT galleries. The gradual redshift of pi-pi* transition peak of PF with increasing MMT content in composites confirms the uncoiling of PF in clay galleries. The photoluminescence characteristics reveal interruption of interchain interaction in this intercalated and exfoliated organic/inorganic hybrid system, which reduces the low-energy emission that results from keto defect. Due to very high aspect ratio of MMT, it can act as an efficient exciton blocking layer and a barrier to oxygen diffusion, which may lead to a device with high color purity and enhanced photostability. Again current-voltage characteristics of nanocomposite films confirm the retention of LED properties after nanocomposite formation. (C) 2011 Elsevier Inc. All rights reserved

MoS₂ Quantum Dot Modified Electrode: An Efficient Probe for Electrochemical Detection of Hydrazine

The development of an effective sensor system that can detect carcinogenic hydrazine is of prime scientific interest for the protection of human health and the environment. In the present study, MoS2 quantum dots (QDs) with an average diameter of ~5 nm were synthesized using a facile one-step, bottom-up hydrothermal method using cysteine as reducing as well as capping agents. The presence of cysteine was evaluated by FTIR spectroscopy. The synthesized MoS2 QDs were applied to modify the conventional glassy carbon electrode (GCE) in order to detect hydrazine electrochemically in neutral pH conditions. In the cyclic voltammetry (CV) study, the MoS2 QDs-modified electrode revealed much better catalytic activities for hydrazine electro-oxidation compared to the bare GCE surface. The smaller size of the QDs with high surface area and the presence of carboxylic acid containing cysteine on the surface of the QDs enhanced the adsorption as well as the electrocatalytic activity. The amperometric response of MoS2-QD-modified GCE unveiled excellent electrocatalytic sensing properties towards neurotoxic hydrazine with a very high sensitivity of 990 μAmM−1cm−2 (R2 = 0.998), low LOD of 34.8 μM, and a broad linear range. Moreover, this high-sensitive, binder and conducting filler-free MoS2-QD-based sensing system is very promising in agile amperometric detection of neurotoxic hydrazine for environmental monitoring in industrial sectors

Suppression of keto defects and thermal stabilities of polyfluorene-kaolinite clay nanocomposites

A solution blending process for preparation of polymer nanocomposites composed of cationic polyfluorene (PF) and dimethyl sulfoxide (DMSO) -intercalated kaolinite (Ka) clay has been taken to evaluate the effect of Ka nanostructure on the nanocomposite structures, morphology, and properties. Composites containing 2, 5, 7.5, and 10 wt % clay have been characterized with the help of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), UV-visible spectroscopy, photoluminescence studies, etc. Additionally, the keto defect, inhibition of interchain interaction; and photostability of PF in the nanocomposites have been explored. The XRD and HRTEM studies show the exfoliation of Ka layers at lower content in composites. Intercalation of PF chains into the Ka interlayer space occurs at relatively higher clay content. Nanocomposites exhibit higher thermal stability than pristine PF due to lamination of PF into clay nanogallery through the interchange of DMSO by cationic polyfluorene. The presence of an Si-O-Si stretching band in the composites supports the formation of nanocomposites of PF with Ka. The movement of absorption maxima to higher wavelength indicates the increase of overall conjugation length of PF chains in the nanocomposites. Upon formation of nanocomposite with Ka, the keto defect sites of PF are significantly reduced. This can be attributed to the lamination of single PP chains by Ka interlayer gallery that act as a barrier to oxygen and inhibit the exciton diffusion. Current-voltage characteristics of nanocomposite films have also shown good switching behavior with low forward junction potential

Modeling of dendrite growth in undercooled solution sodium acetate trihydrate

The sodium acetate trihydrate is commonly used as energy storage phase change material in heating pads for body or hand warmer in cold climates. The undercooled melt of sodium acetate trihydrate kept at room temperature results in an exothermic reaction when solidification seed is nucleated. In presentwork, modeling of denritic growth in an undercooled solution of sodium acetate trihydrate has been carried out. The enthalpy method has been used to compute solid-liquid interface growing in undercooled melt. The interface temperature, concentration and grain growth have been modeled considering curvatureeffect and solutal undercooling. A 2-D computational grid of square control volumes has been used and discreatized governing equations were solved explicitly. The crystal anisotropy was imposed explicitly. The results are validated using experimental data

A Synergistic Coassembly of Block Copolymer and Fluorescent Probe in Thin Film for Fine-Tuning the Block Copolymer Morphology and Luminescence Property of the Probe Molecules

Here, we investigate a synergistic coassembly of a block copolymer, polystyrene-<i>b</i>-poly­(4-vinylpyridine) (PS-<i>b</i>-P4VP), and a fluorescent probe molecule, pyrenebutyric acid (PBA), in thin film using block copolymer supramolecular assembly (SMA) strategy for a wide range of compositions tuned by varying the molar ratio (<i>r</i>) of PBA and 4VP units. The PBA molecules form supramolecules with PS-<i>b</i>-P4VP through H-bonding between the carboxylic acid group of 1-pyrenebutyric acid and pyridine ring of P4VP. For compositions <i>r</i> = 0, 0.1, 0.25, and 0.5, the SMAs exhibit cylindrical morphology, whereas for <i>r</i> = 0.75 and 1, the SMAs generate lamellar morphology. Interestingly, it has been observed that the orientation of the microdomains depends on the solvent used for annealing and can be switched reversibly on exposing the SMA films to corresponding solvent. In a nonselective solvent like chloroform, the microdomains are oriented normal to the substrate, whereas in a selective solvent like 1,4-dioxane, the microdomains are oriented parallel. The synergistic coassembly of PS-<i>b</i>-P4VP and PBA in SMAs with higher molar ratio results in a structure-within-structure pattern characterized by two length scales from phase separation of block copolymer and parallel π–π stacking of the pyrene moiety of PBA molecules inside the comb block. The photophysical properties of PBA in different SMAs of varying composition were studied both in solution and in thin film state and compared to pure PBA. The UV–vis study shows the H type of aggregation of PBA molecules inside the comb block by parallel stacking of the pyrene units, and the PBA molecules orient parallel to the substrate when the microdomains are oriented normal to the substrate. The pure PBA molecules in thin film exhibit excimer emission extensively, whereas the PBA molecules in different supramolecular assemblies exhibit emission ranging from monomer to mixture of monomer and excimer. The SMA shows more intense fluorescence emission compared to pure PBA both in solution and in thin film