David L. Allara

Formation and structure of a spontaneously adsorbed monolayer of arachidic on silver

Abstract A stable monolayer assembly can be formed on silver by the spontaneous adsorption (SA) of arachidic acid (CH 3 (CH 2 ) 18 COOH) from hexadecane. IR spectroscopy and optical ellipsometry indicate that the structure is similar to the Langmuir-Blodgett (LB) multilayer assembly of cadmium arachidate on silver. This is a definitive example of the correspondence between the structure of LB and SA assemblies.

Thermal disordering of langmuir-blodgett films of cadmium stearate on sapphire

Abstract The phase behavior of monolayer and multilayer Langmuir-Blodgett films of cadmium stearate on sapphire is studied using pulsed optoacoustic spectroscopy of the methyl and methylene stretching modes. Heating irreversibly disorders monolayer films but multilayers reach a stable configuration which undergoes reversible phase transitions.

Characterization of Thin Films on Glassy Carbon Electrodes by Infrared External Reflection Spectroscopy

The utility of infrared external reflection spectroscopy [IR-ERS] for the characterization of thin organic surface structures on nonmetallic substrates, such as glassy carbon [GC], has been examined. Surface sensitivity as a function of the angle of incidence and polarization was determined by calculations of mean-square electric field values [MSEF1. Band shapes for IR-ERS spectra, obtained at optimum conditions for thin films (80-3500 A) of poly(methyl metharcylate) [PMMA] on GC, were severly distorted compared to those obtained with transmission spectroscopy. The IR-ERS spectra were accurately modeled (±1096) by classical electromagnetic theory, indicating that the distortions resulted from the inherent physical differences between ERS and transmission measurements.. These results also demonstrated the feasibility of performing quantitative IR-ERS at nonmetallic substrates.

Surface Organization of a Spontaneously Adsorbed Monolayer of Arachidic Acid on Silver

Grazing incidence infrared (GI-IR) spectra of spontaneously adsorbed monolayers of arachidic acid on ambient silver surfaces have been recorded. These spectra are very similar to previously obtained measurements on Langmuir - Blodgett (L-B) deposited films prepared from the corresponding carboxylate salts indicating great similarity between the L-B and spontaneously formed films. The acidic head group has reacted with the silver/silver oxide surface to form a carboxylate salt. Additionally, the hydrocarbon chains have assumed a planar zig-zag conformation. These chains are oriented approximately normal to the surface. The spectrum of arachidic acid, CH3(CH2 -) 18COOH, indicates an orthorhombic subcell packing arrangement. Studies with isotopically labeled n-alkanoic acids have been carried out to confirm some mode assignments.

Considerations for the Optimization of Infrared External Reflection Spectroscopy (IR-ERS) at Liquid/Solid and Gas/Liquid Interfaces

Classical electromagnetic theory has been used to quantitatively assess the effects of various experimental parameters on the sensitivity of IR-ERS for organic monolayers at liquid/solid (L/S) and gas/liquid (G/L) interfaces. Conditions varied at the G/L were angle of incidence and polarization. Additional conditions examined at the L/S, located in a thin-layer cell (TLC), were solution layer thickness and cell window material. The effects of these variations on sensitivity were determined for a model system consisting of a 30 A layer of C19H39 alkyl chains (C19) at H20/Au and air/H20.