Fabrication of Three-Layer-Component Organoclay Hybrid Films with Reverse Deposition Orders by a Modified Langmuir-Schaefer Technique and Their Pyroelectric Currents Measured by a Noncontact Method.

Abstract

In an aqueous clay mineral (montmorillonite) dispersion at a low concentration, isolated clay nanosheets with negative charges were suspended. When a solution of amphiphilic octadecylammonium chloride (ODAH(+)Cl(-)) was spread on an air-dispersion interface, the clay nanosheets were adsorbed on the ODAH(+) cations at the interface to form a stable ultrathin floating film. The floating film was transferred onto a substrate by the Schaefer method, and then the film was immersed in a [Ru(dpp)3]Cl2 (dpp = 4,7-diphenyl-1,10-phenanthroline) solution. The Ru(II) complex cations were adsorbed on the film surface because the film surface possessed a cation-exchange ability. The layers of ODAH(+), clay nanosheets, and [Ru(dpp)3](2+) were deposited in this order. By repeating these procedures, three-layer-component films were fabricated (OCR films). In a similar way, three-layer-component films in which the layers of [Ru(dpp)3](2+), clay nanosheets, and ODAH(+) were deposited in the reverse order (RCO films) were prepared by spreading a [Ru(dpp)3](ClO4)2 solution and immersing the films in an ODAH(+)Cl(-) solution. Both OCR and RCO films were characterized by surface pressure-molecular area (π-A) curve measurements, IR and visible spectroscopy, and the XRD method. The OCR and RCO film systems possessed nearly the same properties in the densities of ODAH(+) and [Ru(dpp)3](2+) and the tilt angle of the Ru(II) complex cation, although the layer distance for the RCO film was a little longer than that for the OCR film and the layered structure for the RCO film was less ordered than that for the OCR film. Pyroelectric currents for the films were measured by a noncontact method using an (241)Am radioactive electrode. When the films were heated, the pyroelectric currents were observed and the current directions for the OCR and RCO films were different. This was clear evidence that the layer order in the OCR film was reverse of that in the RCO film.