The intercalation of quaternary alkylammonium cations into the interlayer gallery of layered silicates by cation exchange processes and the preparation of polymer nanocomposites of these functionalised materials has meanwhile been broadly investigated. When cationic dyes are used for the ion exchange intense metachromic bands in the UV-Vis spectra are typically obtained due to the formation of aggregates of dye molecules after adsorption onto clay surfaces.
The well-known metachromasy of intercalated Basic Red 1 was used to characterise the intercalation behaviour of this dye into different clays. The clays being used in the present work were two synthetic smectites (Laponite RD and Laponite WXFN) and montmorillonite (Nanomer G-105 PGV) from a natural source.
As a next step these results were used to prepare photochromic layered silicates from the two synthetic clays and acridicinium bromide. The photochromism of the latter in aqueous solution is well-known. Upon irradiation with UV-light of a suitable wavelength photo-dimers are formed. During this reaction the colour turns from yellow to colourless. This reaction is reversible by irradiating of the photodimer with UV-light of higher energy. After intercalation of acridicinium bromide an improved photochromism was found as compared to this organic cation in aqueous solution. It was concluded that this improved photochromism was a result of a pre-orientation of the aromatic groups of the dye in the interlayer gallery.
As a second approach in the present work the known benzophenone-based, photo-induced reaction for covalent polymer/clay coupling was investigated. Laponite RD was functionalised with benzophenone by either reacting the edges of the platelets with an adequate silane derivative or by top/bottom modification following a cation exchange approach with a cationic derivative. After dispersing of the modified clay particles in polystyrene the Young's modulus after irradiation of the composites with UV-light was determined and discussed.