Spectroscopic and microscopic study of aggregate formation in the nano-dimensional Langmuir-Blodgett films of perylene with a fatty acid/polymer

Ghosh, Indra; Pal, Amlan J.; Mishra, Bijay K.; Nath, Ranendu Kumar

doi:10.1080/15421406.2015.1069442

Cited by 3 publications

(1 citation statement)

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“…The mixtures of cholesteryl n -alkanoates are further analyzed using Crisp’s surface phase rule. When the external temperature and pressure are fixed, the degrees of freedom are given by the following equation where F , C , P b , and P s are degrees of freedom, the number of components, the number of bulk phases, and the number of surface phases, respectively. For ChC8/ChC9 and ChC18/ChC9 mixtures, we have C = 4 (air, water, ChC9, and ChC8/ChC18), P b = 4 (air, water, bulk crystals, and a homogeneous phase), and P s = 1 (gaseous phase) yielding F = 0, which indicates that the collapse pressure of the mixture is independent of the composition.…”

Section: Resultsmentioning

confidence: 99%

The Role of Molecular Packing in Dictating the Miscibility of Some Cholesteryl n-Alkanoates at Interfaces

Xavier

Viswanath

2021

Langmuir

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Cholesteryl n-alkanoates of saturated fatty acids and their mixtures are widely studied in different physical states and also due to their significance in biology. Here, we address the miscibility of some homologues of cholesteryl n-alkanoates at interfaces, which are known to exhibit different (cholesteryl octanoate, ChC8, and cholesteryl stearate, ChC18) or the same (cholesteryl nonanoate, ChC9, and cholesteryl laurate, ChC12) molecular packing in bulk. Surface manometry and Brewster angle microscopy studies on ChC8 (cholesteryl–cholesteryl interaction, referred to as m-i packing)/ChC9 (cholesteryl–chain interaction, referred to as m-ii packing) and also on ChC18 (chain–chain interactions, referred to as the crystalline bilayer)/ChC9 mixtures reveal phase separation at the air–water (A–W) interface plausibly due to the difference in the molecular packing. In contrast, ChC12/ChC9 (both m-ii packing) mixtures form a homogeneous phase and exhibit a higher collapse pressure (almost twice) than that of ChC9 indicating higher stability. At the air–solid (A–S) interface, the height profiles extracted from the surface topography images using an atomic force microscope yielded thicknesses of 3.6 ± 0.1 and 5.6 ± 0.1 nm for ChC18/ChC9 mixtures (at 0.66 and 0.5 mole fractions (MF)) corresponding to individual assembly, whereas a uniform thickness of 3.5 ± 0.2 nm is obtained for the case of ChC12/ChC9 mixtures (at 0.2, 0.5, and 0.8 MF) corresponding to m-ii packing. Ellipsometry studies reveal that the desorption temperature increases with the mole fraction of ChC9 and attains a maximum at 406.8 ± 4.8 K for 0.4 MF of ChC9, beyond which it decreases. Raman spectroscopy studies are carried out for ChC12/ChC9 mixtures in the homogeneous phase and in the collapsed state. Here, the dependency of peak positions on different physical states was assessed. Our studies offer new insights into the compatibility of molecular packing influencing the phase behavior and may be of relevance to tear film studies and on the formation of crystals in atherosclerosis.

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Section: Resultsmentioning

confidence: 99%