SOLID-STATE NMR-STUDIES OF SELF-ASSEMBLED MONOLAYERS

Octadecylsiloxane (OTS) and zirconium octadecylphosphonate (ODPA) partial monolayers on nonporous silica were characterized by C-13 and P-31 CPMAS NMR. Well-oriented monolayers display an intense peak at 33 ppm, the characteristic C-13 chemical shift of the interior methylene carbons of the alkane chains in an all trans conformation, in addition to a smaller component at 30 ppm corresponding to conformationally disordered chains. In the case of the OTS self-assembled monolayers, both the NMR and FTIR spectra showed an increased extent of ordering of the chains with lower deposition temperatures and a reversible disordering with heating after deposition. The ODPA monolayer on zirconated silica represents the first example of a well-ordered metal phosphonate monolayer prepared by self-assembly techniques alone.