Recent developments in the modeling of the monolayers structure at the water/air interface

Dynarowicz, Patrycja

doi:10.1016/0001-8686(93)80029-b

Cited by 30 publications

(14 citation statements)

References 94 publications

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“…According to the Demchak-Fort model [20], µ ⊥ is composed of three independent contributions arising from (i) orientation of water dipoles in the vicinity of the headgroups, (ii) the headgroup dipoles, and (iii) the hydrophobic part dipoles. Moreover, in our calculations we assumed, as it is made customary [19,21], that ε r = 1, although it is known that dipoles in a monolayer may be embedded in media with distinct, nonunity dielectric constant values, which depends on whether these dipoles are at the monolayer-water or monolayer-air interface [22,23].…”

Section: Table IImentioning

confidence: 99%

Molecular Interactions in Monolayers οf Azo Dye/Liquid Crystal Mixtures at Interfaces

2009

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A study of azo dye/liquid crystal mixtures in monolayers formed at an air-water interface (the Langmuir films) and at a solid surface (the Langmuir-Blodgett films) has been performed. Five azo dyes with various molecular structure and the liquid crystal 4-octyl-4 -cyanobiphenyl (8CB) have been used. The dyes have been added to the liquid crystal at various molar fractions. Surface pressure and surface potential versus mean molecular area isotherms for the Langmuir films have been recorded and information about intermolecular interactions at the air-water interface has been obtained. On the basis of electronic absorption measurements for the Langmuir and Langmuir-Blodgett films the conclusions about the ability of dyes molecules to form self-aggregates at the interfaces have been drawn. The influence of the dye molecular structure and its concentration on aggregates' geometry has been found.

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Section: Table IImentioning

confidence: 99%

Molecular Interactions in Monolayers οf Azo Dye/Liquid Crystal Mixtures at Interfaces

2009

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“…The experimental surface potential changes of a monolayer have usually been interpreted in the terms of so-called effective dipole moments (

). In the simplest approach, derived from the parallel plate condenser model [ 9 ],

is expressed by the Helmholtz equation:

where

is the dielectric permittivity of the film,

is the dielectric permittivity of the vacuum,

. is the normal (to the interface) component of the dipole moment of the film molecule at the interface (note that this is different from the molecular dipole moment of the free molecule) and

is the average area occupied by the molecule at the surface (

, where

is the total number of molecules at 1 cm 2 of the surface).…”

Section: Introductionmentioning

confidence: 99%

“…The above equation applies to un-ionized molecules. For ionized ones, the double layer potential (

) must be taken into account [ 9 , 10 ]. The main problem in Equation (1) is the unknown value of the permittivity of the film,

.…”

Section: Introductionmentioning

confidence: 99%

Electrical Properties of Membrane Phospholipids in Langmuir Monolayers

et al. 2021

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Experimental surface pressure (π) and electric surface potential (ΔV) isotherms were measured for membrane lipids, including the following phosphatidylcholines (PCs)—1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC); 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC); 1,2-diarachidoyl-sn-glycero-3-phosphocholine (DAPC); and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). In addition, other phospholipids, such as phosphatidylethanolamines (represented by 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE)) and sphingolipids (represented by N-(hexadecanoyl)-sphing-4-enine-1-phosphocholine (SM)) were also studied. The experimental apparent dipole moments (μAexp) of the abovementioned lipids were determined using the Helmholtz equation. The particular contributions to the apparent dipole moments of the investigated molecules connected with their polar (μ⊥p) and apolar parts (μ⊥a) were theoretically calculated for geometrically optimized systems. Using a three-layer capacitor model, introducing the group’s apparent dipole moments (calculated herein) and adopting values from other papers to account for the reorientation of water molecules (μ⊥w/εw), as well as the for the local dielectric permittivity in the vicinity of the polar (εp) and apolar (εa) groups, the apparent dipole moments of the investigated molecules were calculated (μAcalc). Since the comparison of the two values (experimental and calculated) resulted in large discrepancies, we developed a new methodology that correlates the results from density functional theory (DFT) molecular modeling with experimentally determined values using multiple linear regression. From the fitted model, the following contributions to the apparent dipole moments were determined: μ⊥w/εw=−1.8±1.4 D; εp=10.2±7.0 and εa=0.95±0.52). Local dielectric permittivity in the vicinity of apolar groups (εa) is much lower compared to that in the vicinity of polar moieties (εp), which is in line with the tendency observed by other authors studying simple molecules with small polar groups. A much higher value for the contributions from the reorientation of water molecules (μ⊥w/εw) has been interpreted as resulting from bulky and strongly hydrated polar groups of phospholipids.

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“…The amount of energy per unit area required is referred to as surface tension; the process also depends on aspects such as: nature of liquid, surrounding medium, and temperature [49]. To prevent the collapse of molecules/particles with respect to each other, the reduction of surface tensions must be measured thoroughly and throughout the process; this is also known as the surface pressure [50][51][52]. The surface pressure is measured by immersing a plate (Wilhelmy plate) across the air/water interface and measuring the downward force (mN/m) experienced by this plate [53,54].…”

Section: Langmuir-blodgett Filmsmentioning

confidence: 99%