Orientation and Electronic Structure of Ion Exchanged Dye Molecules on Mica: An X-Ray Absorption Study

Pulsed Electric Linear Dichroism of Triphenylmethane Dyes Adsorbed on Montmorillonite K10 in Aqueous Media

“…Based on the calculated ELD data, simple models could be proposed for CV and MG molecules bound to clay in aqueous suspension. These results are surprisingly in good agreement with previous observations of CV and MG adsorbed on muscovite mica substrates in the solid states (23).…”

“…The fourth model is presented in (d), where the triangular dye plane is rolled and tilted, being in contact with the surface of the MK-10 particle at one of three apexes (one-site binding). It is interesting to note that a similar binding mode was proposed for methylene blue (21,22), and CV and MG (23), adsorbed on silica and mica substrates in the solid phase. No rational answer can, however, be given for the question of why the hydrophobic dye plane is rolled and tilted away from the clay surface, which is surrounded by a hydrated sheath in aqueous solutions.…”

“…These results verify quantitatively the conclusion by Chernia et al (17) that the bound CV + species, if stacked, are not parallel to the clay surface. It should be pointed out that the nonparallel adsorption mode of CV and MG dye molecules on muscovite mica substrate in the solid phase is also reported by Fischer et al (23). Interestingly, such oblique adsorption modes of dyes were proposed for rectangular stilbazolium in aqueous suspensions (1) and methylene blue on solid-phase substrate (21,22).…”

“…This assumption must, however, be verified, since there is the possibility that the dye molecules are distorted upon binding to the surface of the MK-10 particle or upon intercalation between the layers, or that the dye may be inherently nonplanar and tripodlike (23). If the directions of the three polarizations (x, y, z) are mutually orthogonal, the following relationship should hold:…”

“…This information is difficult to obtain from other physico-chemical methods, such as second harmonic generation (SHG) (21), near-edge X-ray absorption spectroscopy (NEXAFS), and X-ray photoelectron spectroscopy (XPS) (22,23). For the present purpose, the ELD spectra of two monocationic triphenylmethane dyes, crystal violet (hereafter abbreviated as CV) and malachite green (hereafter abbreviated as MG), were measured in the presence of MK-10 under conditions closely related to the electric birefringence measurements of MK-10 itself (19,20).…”