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Titolo:
The structures of Langmuir-Blodgett films of fatty acids and their salts
Autore:
Peng, JB; Barnes, GT; Gentle, IR;
Indirizzi:
Univ Queensland, Dept Chem, Brisbane, Qld 4072, Australia Univ QueenslandBrisbane Qld Australia 4072 Brisbane, Qld 4072, Australia
Titolo Testata:
ADVANCES IN COLLOID AND INTERFACE SCIENCE
fascicolo: 2, volume: 91, anno: 2001,
pagine: 163 - 219
SICI:
0001-8686(20010525)91:2<163:TSOLFO>2.0.ZU;2-X
Fonte:
ISI
Lingua:
ENG
Soggetto:
X-RAY-DIFFRACTION; ATOMIC-FORCE MICROSCOPY; AIR-WATER-INTERFACE; REFLECTION-ABSORPTION-SPECTROSCOPY; OMEGA-TRICOSENOIC ACID; CADMIUM ARACHIDATE MONOLAYERS; INTEGRATED OPTICAL TECHNIQUES; ORDER-DISORDER TRANSITIONS; FT-IR SPECTROSCOPY; BUILT-UP FILMS;
Keywords:
fatty acids; Langmuir-Blodgett films; structure determination; grazing incidence; X-ray diffraction; monolayers;
Tipo documento:
Review
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
234
Recensione:
Indirizzi per estratti:
Indirizzo: Gentle, IR Univ Queensland, Dept Chem, Brisbane, Qld 4072, Australia Univ Queensland Brisbane Qld Australia 4072 ld 4072, Australia
Citazione:
J.B. Peng et al., "The structures of Langmuir-Blodgett films of fatty acids and their salts", ADV COLL IN, 91(2), 2001, pp. 163-219

Abstract

Recent advances in several experimental techniques have enabled detailed structural information to be obtained for floating (Langmuir) monolayers andLangmuir-Blodgett films. These techniques are described briefly and their application to the study of films of fatty acids and their salts is discussed. Floating monolayers on aqueous subphases have been shown to possess a complex polymorphism with phases whose structures may be compared to those of smectic mesophases. However, only those phases that exist at high surfacepressures are normally used in Langmuir-Blodgett (LB) deposition. In single LB monolayers of fatty acids and fatty acid salts the acyl chains are in the all-cans conformation with their long axes normal to the substrate. Thein-plane molecular packing is hexagonal with long-range bond orientationalorder and short-range positional order: known as the hexatic-B structure. This structure is found irrespective of the phase of the parent floating monolayer. The structures of multilayer LB films are similar to the structures of their bulk crystals, consisting of stacked bilayer lamellae. Each lamella is formed from two monolayers of fatty acid molecules or ions arranged head to head and held together by hydrogen bonding between pairs of acids or ionic bonding through the divalent cations. With acids the acyl chains are tilted with respect to the substrate normal and have a monoclinic structure, whereas the salts with divalent cations may have the chains normal to the substrate or tilted. The in-plane structures are usually centred rectangular with the chains in the trans conformation and packed in a herringbone pattern, Multilayer films of the acids show only a single-step order-disorder transition at the malting point, This temperature tends to rise as the number of layers increases. Complex changes occur when multilayer films of the salts are heated. Disorder of the chains begins at low temperatures but the arrangement of the head groups does not alter until the melting temperature is reached, Slow heating to a temperature just below the melting temperature gives, with some salts, a radical change in phase. The lamellar structure disappears and a new phase consisting of cylindrical rods lying parallel to the substrate surface and stacked in a hexagonal pattern is formed, In each rod the cations are aligned along the central axis surrounded by the disordered acyl chains. (C) 2001 Elsevier Science B,V. All rights reserved.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 12/07/20 alle ore 13:24:09