2- [4'-Ethyloctadecylamino-or 2- [4'-dioctadecylamino-phenylazo] -N-methylbenzothiazolium perchlorates (hereafter referred to as azo I and azo II) were synthesized, and the properties of their monolayers on a water suface and the Langmuir-Blodgett (LB) films were investigated. It was found that these dyes formed stable monolayers at the air-water interface, and Y-type monolayer assemblies could be obtained. The visible absorption spectra of the LB films showed that azo I did not form an H aggregate in the film while azo II formed it. A comparision of the infrared transmission and reflection-absorption (RA) spectra revealed that the benzothiazolium rings of azo I and azo II are fairly perpendicular to the substrate surface but their benzene rings are tilted appreciably. It was also found that the long alkyl chains were neither perpendicular nor parallel to the substrate surface, being considerably inclined. The hydrocarbon chains of azo II had highly ordered (trans-zigzag) structure but that azo I was slightly less ordered in the films. Depth distribution of the higher order structure of the LB films deposited on an Au Plate is examined by XPS, and the tickness per monolayer for azo I and azo II was estimated to be 1.8 and 2. 1 nm, respectively.
The effects of heat treatment and acidic and basic vapor phase treatments on Langmuir-Blodgett (LB) films of2- [4'- (n-octadecylamino) -or 4'- (dioctadecylamino) -1'-naphthylazo] N-methylbenzothiazolium perchlorates (azo V and azo VI) have been studied. The as-deposited films of azoV and azoVI exhibited H-like aggregate bands at 419 and 427nm in UV-visible absorption measurement, respectively. After HC1 vapor treatment, the H-like band for azo VI disappeared and a monomeric band (M) appeared at 557nm. The films that had dissociated by the acid treatment exhibited an Hlike band (at 475nm), which differed from the original H-like band after the heat treatment, and also exhibited a band at ca. 429nm after the base treatment (exposure to NH3 vapor or immersion into NaOH aqueous solution). The repetition of the heat and acid treatments caused a reversible change between M and H-like states. Similar optical changes were also obtained for azoV films. Apart from the evidence for the gas penetration into the LB films under the employed conditions, the IR spectra of the films were correlated closely with the corresponding visible absorption spectra.
The manufacturing of wet-coated magnetic recording media requires the dispersion of the magnetic particles in a blend of resin components and solvents. For the optimum in quality of the product the magnetic particles have to be ideally dispersed, the resulting dispersion should be stable over a period of at least 24 hours and the dispersing agents should have a neutral or positive effect on the final properties of the coating. It is now reported, that AB-block copolymers are advantageous for the dispersion of magnetic pigments. Compared to conventional polymeric dispersants frequently based on vinyl chloride copolymers, a higher rate of dispersion is achieved. The influence of the structure of the dispersant on the dispersing properties is discussed.