Molecular orientation of methylene blue intercalated in layer-charge-controlled montmorillonites

The effect of the layer-charge density of clay on the orientation and aggregation of a cationic dye, methylene blue (MB), in MB/clay films was investigated using a series of layer-charge-controlled montmorillonites as host materials. Polarized ultraviolet-visible spectroscopy and x-ray diffraction were used for the characterization of the arrangement and orientation of dye cations in host interlayer spaces. It was revealed that high charge densities of layers induced the formation of relatively ordered and homogeneous phases with dye dimers. The reduction of the charge led to the formation of disordered, mixed phases with large amounts of monomers (isolated dye cations). Dimers and monomers were slightly tilted against the plane of the clay surface, and their angles were not affected by the layer charge.