No abstract

The adsorption and intercalation of the cationic luminescence probe, tris(2,2′-bipyridine)ruthenium(II) complex ([Ru(bpy) 3 ] 2+ or Rubpy), into hectorite and Laponite host clay films were investigated. Because the photophysical properties of Rubpy are strongly influenced by the lamellar nanospace of the smectite host, Rubpy serves as a unique photoprobe of host-guest and guest-guest interfaces within inorganic-organic nanocomposites. The stacking patterns of the host tactoids influence guest luminescence through direct mediation of ion clustering and self-quenching phenomena. Spectral red shift of emission wavelengths and decreased lifetimes were observed with increased guest loading. The extent of red shift in the Rubpy/Laponite films indicated a more fluid guest microenvironment. Rubpy/Laponite films exhibit enhanced potential for photonic and sensor applications with increased optical transparency, intense luminescence, and longer luminescence lifetimes. Cointercalation of the cationic surfactant, trimethylcetylammonium cation, promotes two-dimensional tiling of Laponite tactoids and may afford selective tuning of fluorophore packing.

Exposing layered silicate materials such as hectorite and montmorillonite to aniline vapor results in spontaneous surface polymerization as well as intergallery polymerization of the organic monomer. The inorganic−organic assemblies produced in these reactions possess many unique chemical and electronic properties, including the ability to function as chemical sensors. We have studied the polymerization of aniline on the surface of Cu(II)-exchanged hectorite thin films. The in-situ nucleation and growth of these polymer films is studied for the first time using the technique of scanning force microscopy (SFM) phase contrast imaging. A novel mechanism for the nucleation and growth of the surface polymer film is proposed. The availability of Cu(II) cations via defects or faults in the layered silicate structure is crucial to the formation of the subsequent conductive polymer layer.

Laponite films provide versatile inorganic scaffolds with materials architectures that direct the self-assembly of CdSe quantum dots (QDs or EviTags) and catalytic surfaces that promote the in situ polymerization of polyaniline (PANI) to yield novel nanocomposites for light emitting diodes (LEDs) and solar cell applications. Water-soluble CdSe EviTags with varying, overlapping emission wavelengths in the visible spectrum were incorporated using soft chemistry routes within Na-Laponite host film platforms to achieve broadband emission in the visible spectrum. QD concentrations, composition and synthesis approach were varied to optimize photophysical properties of the films and to mediate self-assembly, optical cascading and energy transfer. In addition, aniline tetramers coupled to CdSe (QD-AT) surfaces using a dithioate linker were embedded within Cu-Laponite nanoscaffolds and electronically coupled to PANI via vapor phase exposure. Nanotethering and specific host-guest and guest-guest interactions that mediate nanocomposite photophysical behavior were probed using electronic absorption and fluorescence spectroscopies, optical microscopy, AFM, SEM, powder XRD, NMR and ATR-FTIR. Morphology studies indicated that Lap/QD-AT films synthesized using mixed solvent, layer by layer (LbL) methods exhibited anisotropic supramolecular structures with unique mesoscopic ordering that affords bifunctional networks to optimize charge transport.

Graphene-polyaniline (GP) nanocomposites have demonstrated remarkable ability as supercapacitive materials and are typically synthesized via chemical reduction of graphene oxide/polyaniline (GOP) precursors. We report the formation of novel nanomaterials combining GOP nanocomposites with Laponite nanodisks. Host-guest interactions within GOP systems were studied with and without Laponite nanoparticle templating agents. Incorporating Laponite clay into the composite synthesis enhances aqueous dispersibility as well as facilitates the casting of homogeneous films. Structural and morphological characterization confirmed porous heterointerfaces and control of polymer and nanoclay loading. These results may enable the development of flexible supercapacitive and solar nanocomposites with improved device utility, water dispersibility, and film processability. We demonstrate that these films can be easily cast and that the composites maintain their electrical transport properties.