Nanocomposite Films Derived from Exfoliated Functional Aluminosilicate through Electrostatic Layer-by-Layer Assembly

Multilayered nanocomposite films were prepared from aluminosilicate platelets with functional chromophores and polyelectrolytes through electrostatic layer-by-layer assembly. Fluorescent dye coumarin was intercalated into the layered aluminosilicate hectorite, and the resulting hectorite/coumarin intercalation complex particles were broken down into individual platelets by means of extensive shaking and sonication of their water suspension. Atomic force microscopy (AFM) and transmission electron microscopy data show that the exfoliated platelets have the form of lathes of approximately 10−40 nm width, 150−400 nm length, and 2−3 nm average thickness. This last value is consistent with the overall thickness of a single aluminosilicate lamella sheathed with coumarin molecules on both sides. Given the strong negative surface charge of the aluminosilicate layers, films of nanocomposites could be formed by electrostatic layer-by-layer assembly using a cationic polyelectrolyte. The AFM topography of such films revealed a homogeneous monolayer coverage of the underlying substrate. Linear buildup of the multilayer films of up to 20 cycles was demonstrated and investigated using UV/vis absorption spectroscopy. The resulting transparent films have exhibited strong characteristic blue-green fluorescence due to coumarin dye molecules adhered to the exfoliated hectorite platelets.