Stability Of Langmuir Research Articles

Atomic composition and stability of Langmuir–Blodgett monolayers based on siloxane dimer of quaterthiophene on the surface of polycrystalline gold

Atomic composition of monolayers based on siloxane dimer of quaterthiophene deposited by Langmuir–Blodgett technique on a silicon dioxide surface partially covered by gold film and the stability of these monolayers upon surface treatment by Ar+ ions bombardment have been studied. Experimental results for the chemical composition of a series of studied surfaces have been obtained by X-ray photoelectron spectroscopy (XPS) by recording XPS spectra of C 1s, O 1s, S 2p, and Au 4f core levels. The relative concentration of Au and Si substrate atoms and the composition of ex situ prepared surface under study were determined within 10–15%, which indicates that Langmuir–Blodgett monolayers based on siloxane dimer of quaterthiophene form continuous coating in a considerable extent. Prior to the treatment of the studied surface by Ar+ ions bombardment, carbon- and oxygen-containing surface adsorbates provided a considerable contribution to the results of XPS measurements. The surface cleaning by Ar+ ions with energy 3 keV at electric current through sample of ~1 μA in several 30-s steps has led to the etching of surface adsorbates and next Langmuir–Blodgett films of the siloxane dimer of quaterthiophene.

Supramolecular structures formed from heterocyclic aromatic molecules

This paper describes the formation and structure investigation of Langmuir monolayers and Langmuir-Blodgett multilayers formed from amphiphilic derivatives of 2,5-diphenyl-1,3,4-oxadiazole. The 2,5-diphenyl-1,3,4-oxadiazole group as a functional unit with interesting physical and chemical properties is maintained, while the head group, the length of the alkyl chain and the structure of the coupling unit between aromatic and aliphatic part of these linear short-chain amphiphiles is systematically varied in order to explore the influence of this change on the film forming properties and the stability of Langmuir and Langmuir-Blodgett films. Molecular mechanics simulations are shown by these systematic variations to be suitable for the prediction of optimal chemical structures allowing for a stable stratified molecular packing. The combination of a detailed structure investigation of the multilayers based on scanning force microscopy and X-ray data with molecular mechanics simulations yields an insight into the packing of the molecules and the intermolecular interactions.

Monolayers and Multilayers of Uranyl Arachidate 2. Influence of the Subphase pH on the Structure and Stability of Langmuir−Blodgett Films

In this second paper we describe the comprehensive structure investigations on multilayers of uranyl arachidate formed by Langmuir−Blodgett deposition from subphases of different pH on solid substrates by means of a combination of infrared spectroscopy, X-ray specular reflection, ellipsometry, and scanning force microscopy. The structure of these multilayers and their stability are obviously influenced by the subphase pH. The pH range of the acid to salt conversion determined for the Langmuir films is confirmed by the infrared spectroscopic data of the multilayers. While arachidic acid films, deposited from an uranyl acetate subphase of low pH, are found to have a strongly distorted rough surface, the films of uranyl arachidate formed at higher subphase pH are smooth and have a quite regular and stable multilayer structure. The influence of the counterions on the alkyl chain conformation, chain packing, reorganization probability, and stability of the multilayers is discussed.