No abstract

Monolayers were formed from alkyl chain molecules having large in-plane dipole moments. The molecular species introduced was a sulfone moiety, and it was found that its incorporation strongly affected the molecular conformation within the monolayer. The effect of varying the position of the sulfone group in an otherwise straight alkyl chain, while constant molecular length was maintained, was studied, and the results were compared to those found for an octadecanethiol (ODT). The monolayers were characterized by Fourier transform infrared reflection absorption spectroscopy and X-ray photoelectron spectroscopy and by their wetting properties.

Poling, which involves the alignment of nonlinear optical (NLO) dipolar molecules in the direction of the applied electric field, was carried out using constant current charging, a recently developed corona charging technique. Using this technique, the sample surface voltage buildup, and hence the efficiency of the dipole alignment, can be monitored during the poling process. In addition, it will be shown that this capability also provides a way to detect the end point of the dipolar orientation. Corona charging of the organic NLO film used in this study, however, needs to be done in an inert atmosphere. Results from in situ IR spectroscopy measurement during corona charging of the NLO film, ultraviolet and visible absorption spectroscopy and electron scattering for chemical analysis of this film before and after poling, indicated that exposing it to corona discharge in air ambient caused oxidation of the polymer surface. Various types of nitrogen oxides and carboxylic acids were found to be the products of this oxidation reaction. Finally, we also obtained evidence showing that the surface charging process of the organic NLO film is affected by this newly grown oxidized layer.

The interfacial chemistry between evaporated Ag and poly(p-phenylene sulfide) (PPS) has been investigated with x-ray photoelectron spectroscopy (XPS). The initial stages of nucleation and growth of Ag in the subatomic-layer regime were monitored. The PPS core level spectra exhibit no detectable changes as a function of Ag coverage; however, the Ag 3d5/2 peak position shifts ∼0.6 eV to higher binding energy at low Ag coverages. At low Ag coverages, the valence band spectra consist of two main features centered at 2.5 and 5.9 eV. Unrestricted Hartree–Fock (UHF) molecular orbital calculations suggest that the 5.9 eV band consists of weakly perturbed Ag 4d orbitals and bonding Ag 4d–S 3p hybrid orbitals. The 2.5 eV band consists of antibonding Ag 4d–S 3p hybrid orbitals. Molecular mechanics results suggest that the sulfur atom transforms from a bent to either a trigonal pyramidal or trigonal planar configuration after bonding with Ag. Both the molecular orbital calculations and molecular mechanics results suggest that the trigonal pyramidal configuration is more favorable.

46) Chapter 2 of ref 3 contains an excellent discussion of polymer structure, relaxations, and transitions in regard to polymer surface dynamics.