ROLE OF THE TEMPLATE LAYER IN ORGANIZING SELF-ASSEMBLED FILMS - ZIRCONIUM PHOSPHONATE MONOLAYERS AND MULTILAYERS AT A LANGMUIR-BLODGETT TEMPLATE

Organophosphonate monolayer and multilayer films have been prepared by self-assembly of organophosphonic acid molecules at a zirconium octadecylphosphonate Langmuir-Blodgett (LB) film. Infrared and XPS analyses of the zirconated LB template layer demonstrate that it is well-ordered and close-packed with a Zr:P ratio of 1:1, indicating that a surface with a high density of zirconium binding sites is produced. Polarized ATR-FTIR measurements reveal that the alkyl chains in the LB template layer are tilted by 31-degrees from the surface normal. Octadecylphosphonic acid is self-assembled at the zirconated LB template to produce a zirconium octadecylphosphonate bilayer. ATR-FTIR spectroscopy of the C-H stretching bands indicates that the self-assembled layer is close-packed and that the alkyl chains are in an all-trans conformation. XPS analysis shows that the bilayer possesses a Zr:P ratio of 1:2 and that every template Zr4+ Site binds one octadecylphosphonic acid molecule from solution. Contact angle measurements on the completed bilayer reveal an advancing contact angle of 110 +/- 1-degree. The tilt angle of the alkyl chains in the self-assembled layer is 22-degrees, as determined by polarized ATR-FTIR, which is contrasted to the 5-degrees tilt angle seen if the octadecylphosphonic acid capping layer is deposited as an LB film. Multilayer films of 1,10-decanediyldiphosphonic acid (DDPA) are also assembled at the zirconated LB template. The layer-by-layer deposition is monitored by integrating the intensity of the nu(a)(CH2) band after each deposition cycle. In the first few layers, the diphosphonic acid molecules bridge zirconium sites on the template layer, but a constant rate of deposition is achieved after three or four layers. Analysis of the fwhm of the nu(a)(CH2) band indicates that close-packed films are not produced. The rigid alpha,omega-diphosphonic acid quaterthiophenediphosphonic acid (QDP) is also assembled layer-by-layer at the zirconated LB template. UV-vis analysis indicates that the same amount of material is deposited after each deposition cycle. X-ray diffraction from 10 layers of QDP reveals a d spacing of 20.19 angstrom, demonstrating the layered nature of the film. The QDP molecules are oriented nearly perpendicular to the surface.