Head-to-tail or head-to-head structure of Langmuir-Blodgett long chain ester multilayers?

doi:10.1016/0040-6090(94)90546-0

Thin Solid Films

Volume 242, Issues 1–2, 15 April 1994, Pages 283-288

https://doi.org/10.1016/0040-6090(94)90546-0 Get rights and content

Abstract

The effect of the deposition velocity on the type of transfer (X-, Y- or XY-) of methylarachidate and methylbehenate monolayers is investigated. To provide conditions for deposition of monolayers, but not of three-dimensional aggregates, the effect of the temperature on monolayer stability at constant surface pressure is followed at first. It is found that the gradual increase of the deposition velocity results in a transition from X- to Y-type transfer of the layers. Transition from X- to Y-type deposition is also observed on increase of the number of deposited monolayers. Small angle X-ray diffraction investigation reveals repeated spacings of a bilayer (head-to-head) structure for Y-type deposition. Structural similarity is found for multilayers built up by either XY- or X-type transfer. The specific electron density profile of the methyl ester films might result in a misleading conclusion about head-to-tail molecular arrangement in the multilayers.

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This paper deals with the characteristics of ethyl palmitate (EP) Langmuir monolayers spread on water and aqueous solutions containing Na⁺ and Ca²⁺. No relevant differences due to the presence of ions were observed in the surface pressure–area (π–A) isotherms at 15, 20 and 25 °C. Brewster angle microscopy (BAM) was applied for a direct visualization of monolayers morphology. Circular and compact domains of liquid expanded (LE)–liquid condensed (LC) transition become dendritic shaped upon temperature increase. On ion-containing subphases, the temperature governs the average LC domain size along the LE–LC transition. During the monolayer collapse, numerous microdomains of high refractive index appear, indicating the transformation of the monolayer into three-dimensional (3D) structures through a nucleation process. For monolayers spread on subphases containing Ca²⁺, independently on temperature, these nuclei are formed at π below the collapse pressure (π_c), on domains fusion. The resistance of monolayer to molecular aggregation depends both on the presence of ions and temperature.
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Head-to-tail or head-to-head structure of Langmuir-Blodgett long chain ester multilayers?

Abstract

J. Colloid Interface Sci.

Thin Solid Films

Colloids Surf.

Thin Solid Films

Thin Solid Films

Adv. Colloid Interface Sci.

J. Colloid Interface Sci.

Phys. Rev.

Science