Fabrication of an anionic polythiophene/layered double hydroxide ultrathin film showing red luminescence and reversible pH photoresponse

Luminescent ordered ultrathin films (UTFs) based on a sulfonated polythiophene (SPT) and Mg–Al‐layered double hydroxide (LDH) nanosheets have been fabricated by the layer‐by‐layer assembly method. UV‐visible absorption and fluorescence spectroscopy showed that there was a stepwise and regular growth of the films with increasing number of deposition cycles. XRD, AFM, and SEM showed that the films had a periodic layered structure with a period of ca. 3.0 nm, and that the thickness can be finely controlled within the range ca. 26–100 nm. The SPT/LDH UTFs show well‐defined polarized photoemission with an anisotropy of ca. 0.3, and they show a reversible luminescence response to changes in pH. Periodic density functional theoretical calculations gave a band energy of 1.85 eV for the SPT/LDH system and showed that the valence electrons of SPT can be confined in the energy wells formed by the LDH monolayers, which effectively inhibits both the nonradiative relaxation and the π–π stacking interaction of the polymer chromophores. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Preparation and nonisothermal crystallization behavior of polypropylene/layered double hydroxide nanocomposites

Polypropylene (PP)/layered double hydroxide (LDH) nanocomposites were prepared via melt intercalation using dodecyl sulfate anion modified LDH and maleated PP as compatibilizing agent. Evidently the interlayer anions in LDH galleries react with maleic anhydride groups of PP-g-MA and lead to a finer dispersion of individual LDH layers in the PP matrix. The nanostructure was characterized by XRD and TEM; the examinations confirmed the nanocomposite formation with exfoliated/intercalated layered double hydroxides well distributed in the PP matrix. The nonisothermal crystallization behavior of resulting nanocomposites was extensively studied using differential scanning calorimetry (DSC) technique at various cooling rates. In nonisothermal crystallization kinetics, the Ozawa approach failed to describe the crystallization behavior of nanocomposites, whereas the Avrami analysis and Jeziorny method well define the crystallization behavior of PP/LDH nanocomposite. Combined Avrami and Ozawa analysis (Liu model) also found useful. The results revealed that very small amounts of LDH (1%) could accelerate the crystallization process relative to the pure PP and increase in the crystallization rates was attributed to the nucleating effect of the nanoparticles. Polarized optical microscopy (POM) observations also support the DSC results. The effective crystallization activation energy was estimated as a function of the relative degree of crystallinity using the isoconversional analysis. Overall, results indicated that the LDH particles in nanometer size might act as nucleating agent and distinctly change the type of nucleation, growth and geometry of PP crystals.     

Second staging of tartrate and carbonate anions in Mg–Al layered double hydroxide

The intercalation of tartrate was performed through ion exchange using carbonate Mg–Al layered double hydroxide (LDH) as precursor. The intermediate crystalline phase (so-called second-staging phase) was observed during the intercalation process. The pure second-staging LDH, in which alternate interlayer regions are occupied by carbonate and tartrate anions, was obtained by the deintercalation of interlayer tartrate with carbonate. It was also found that the interlayer tartrates are so stable that they are difficult to exchange by carbonate at room temperature.     

In situ growth of layered double hydroxide films on anodic aluminum oxide/aluminum and its catalytic feature in aldol condensation of acetone

Mg/Al layered double hydroxide (LDH) films were fabricated in situ with anodic aluminum oxide (AAO)/aluminum as both the substrate and the sole aluminum source by means of urea hydrolysis. The structure and morphology of the LDH films were investigated by X-ray diffraction (XRD), attenuated total reflectance-Fourier transform infrared (ATR-FT-IR) and scanning electron microscopy (SEM), which show that hexagonal plate-shaped LDH crystallites grow perpendicularly on the substrate via a strong chemical interaction. After being activated by a calcination/rehydration procedure, the rehydrated LDH (RLDH) platelets remain firmly immobilized on the AAO/aluminum substrate and retain the hexagonal platelet morphology of the LDH precursor. The catalytic activity of the resulting material was tested by using aldol condensation of acetone as a probe reaction, showing that the RLDH/AAO is superior in catalytic performance to the powdered RLDH analogue. The kinetic feature of this catalytic reaction was also analyzed, which suggests that it obeys the D₁ kinetic model, a one-dimensional diffusion-controlled mechanism.     

Synthesis of 5‐sulfosalicylic acid‐intercalated layered double hydroxide and its effects on wood flour/polypropylene composites during accelerated UV weathering

In this study, 5‐sulfosalicylic acid (SA) anions have been intercalated into Mg₃Al‐NO₃ layered double hydroxide (LDH) to synthesize SA‐intercalated Mg₃Al‐NO₃‐LDH (LDH‐SA) by ion‐exchange reaction. Then, the effects of LDH, SA, and LDH‐SA on the photostability of wood flour/polypropylene (WF/PP) composites during accelerated ultraviolet (UV) weathering were investigated. The surface color, surface gloss, and mechanical properties of the composites during weathering were tested, accompanied by characterizations using SEM, ATR‐FTIR, and TG. The results showed that (1) SA anions completely replaced the anions in LDH and the thermal stability of LDH‐SA was considerably enhanced; (2) composites with LDH or LDH‐SA exhibited less color change, fewer surface cracks, better thermal stability, and less losses of mechanical properties than the control group; (3) LDH‐SA showed a long‐term efficiency and alleviated the photo‐oxidation of WF/PP composites successfully; (4) LDH‐SA blocked UV light by physical shield effect of the layer sheets, as well as the chemical absorbability of the interlayer anions. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44597.