Penggang Li

Functions of surfactants in the one-step synthesis of surfactant-intercalated LDHs

Surfactant-intercalated Zn and Al layered double hydroxides (ZnAl-LDHs) were synthesized via spontaneous self-assembly of the surfactants (sodium dodecyl sulfate and sodium dodecyl benzene sulfonate) and the LDH salt precursors. To understand the function of the surfactants in the synthesis, the surfactant-modified ZnAl-LDHs and their intermediates before aging were characterized via X-ray diffraction, Fourier transform infrared spectroscopy, Field emission scanning electron microscopy, and thermogravimetric analysis. In addition, fluorescence spectroscopy was used to in situ trace the microenvironmental variations of the reactants in the synthesis. It was found that the anionic surfactants can interact with the LDH precursors to form cooperative micellar assemblies, which increase the concentration of cationic counter ions around the micelles leading to enhanced growth of the LDH sheets along their lamellar surface direction and the stacking of LDH sheets into nanoparticles as the surfactant possesses longer molecular length. Because of the hydrophobicity of the intermediate sheets coated with surfactants, the reaction between the dissolved CO32− and the LDH intermediate sheets can be greatly reduced, and thus no strict N2 protection was necessary in this method. This mechanistic understanding of the effects of the surfactants on the formation of LDHs is critical in successful synthesis of organic-intercalated LDHs in complicated system by void the interruption of competitive ions.

Polyimide composites composed of covalently bonded BaTiO3@GO hybrids with high dielectric constant and low dielectric loss

Novel flexible three-phase high-k polyimide (PI) composites were fabricated by the incorporation of covalently bonded BaTiO3@graphene oxide (BaTiO3@GO) hybrids in which the BaTiO3@GO hybrids were prepared by the reaction of amino modified BaTiO3 particles and GO. A series of analyses, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Raman and XRD demonstrated that amino modified BaTiO3 particles were successfully grafted onto the surface of GO. A dielectric constant as high as 285 (100 Hz), which was eighty times that of a pure PI film, a lower dielectric loss as low as 0.25 and high-frequency-shift dielectric relaxation were obtained for BaTiO3@RGO/PI composites as the fraction of BaTiO3@GO was 20 wt% (the corresponding volume fraction is 8 vol%). The flexible, high-k BaTiO3@RGO/PI composites have promising potential applications for capacitors and electronic devices in the fields of micro electron.

Contribution of sodium dodecyl sulphate and sodium lauric acid in the one-pot synthesis of intercalated ZnAl-layered double hydroxides

Anion surfactants, sodium dodecyl sulphate (SDS) and sodium lauric acid (SLA), with almost the same chain length but different anion groups were used together as intercalates to prepare intercalated ZnAl–layered double hydroxides (ZnAl–LDHs). Their composition, structure and morphology were characterized by Fourier transform infrared, X-ray fluorescence, thermogravimetric and X-ray diffraction (XRD). The results indicated SDS intended to maintain the lamellae structure of LDHs, but SLA was more likely to expand the basal spacings of LDHs in the present system. The arrangement of the surfactants in the interlayer of ZnAl–LDHs was also simulated by Materials Studio. The basal spacings of the LDHs calculated based on simulated structure consisted with that from XRD.