Molecular Organization in Langmuir Films of Dichroic Azo DyeLiquid Crystal Mixtures. II. Surface Potential Measurements

Two-component films of 4-octyl-4’-cyanobifenyl (8CB) and non-amphiphilic azo dye (1) at different molar fractions were studied at the air-water interface on the basis of the surface potentialmean molecular area dependence recorded simultaneously with the surface pressure-mean molecular area isotherm. Conventional Langmuir technique was used to form 1/8CB (guest-host) films during reduction and expansion of an area occupied by the molecules. From the surface potential value the effective dipole moment in the first monolayer formed on the water was calculated. Moreover, the number of dipole moments directed to the air with respect to those directed towards the water was estimated. A model of the microscopic polar ordering of the molecules in 1/8CB films at the air-water interface is proposed.

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Molecular Organization in Langmuir Films of a Dichroic Azo Dye-Liquid Crystal Mixture. I. Thermodynamic Data and BAM Observations

Zeitschrift für Naturforschung A ◽

10.1515/zna-2003-0103 ◽

2003 ◽

Vol 58 (1) ◽

pp. 23-32

Author(s):

T. Martyński ◽

J. Miyake

Keyword(s):

Mole Fraction ◽

Surface Pressure ◽

Azo Dye ◽

Three Dimensional ◽

Langmuir Films ◽

Molecular Organization ◽

Water Interface ◽

Brewster Angle Microscopy ◽

Phase Rule ◽

Air Water Interface

1Two-component films of 4-octyl-4’-cyanobiphenyl (8CB) and a nonamphiphilic azo dye on an airwater interface have been studied by means of surface pressure-area (π-A) isotherm measurement, Brewster angle microscopy (BAM), and absorption spectroscopy. Conventional Langmuir technique was used to form /8CB (guest-host) films during compression and expansion of an area occupied by the molecules. The pure dye, spread on the air-water interface, formed irregular three-dimensional structures (3D), visible by the naked eye. In 1/8CB films the dye was distributed homogeneously only at low mole fraction. At mole fractions higher than 0.3, just after spreading the 1/8CB solution at the interface part of 1 formed 3D structures. On the basis of π-A isotherm, information about the miscibility of the two components in the 1/8CB mixtures was obtained by using the area additivity criterion and surface phase rule. BAM images allowed to draw conclusions on the molecular organization of mixed Langmuir films at the air-water interface. The presence of 1, roughly up to a mole fraction of 0.5, causes the mixed film to be less compressible and more thermodynamically stable (with higher collapse surface pressure). The absorption spectra of the films of 1/8CB mixtures revealed the formation of dye aggregates.

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Surface properties of some carotenoids spread in monolayers at the air/water interface. Experimental and computational approach

Open Chemistry ◽

10.2478/s11532-006-0017-1 ◽

2006 ◽

Vol 4 (3) ◽

pp. 489-501

Author(s):

Ossi Horovitz ◽

Gheorghe Tomoaia ◽

Csaba Racz ◽

Aurora Mocanu ◽

Liviu-Dorel Bobos ◽

...

Keyword(s):

Surface Properties ◽

Dipole Moments ◽

State Equation ◽

Interaction Parameters ◽

Water Interface ◽

Molecular Area ◽

Collapse Pressure ◽

Pressure Surface ◽

Air Water Interface ◽

Β Carotene

AbstractThe surface pressure versus molecular area isotherms of some carotenoids: β,β-carotene-4-one (echinenone, ECH), β,β-carotene-4,4′-dione (canthaxanthin, CAN) and 4,4′-diapo-ω,ω-carotene-4,4′-dial (APO), spread at the air/water interface, are reported. A van der Waals type state equation is used to describe the high molecular area portions of the compression isotherms and interaction parameters within monolayers are derived. Quantum chemical semi-empirical SCF MO calculations (AM1 and PM3) are performed for the optimized geometries of molecules and dipole moments are calculated. Similar theoretical magnitudes are obtained by both methods. Surface properties, like collapse pressure, surface compressional modulus and interaction parameters are discussed in terms of dipole-dipole interactions, and correlations with the calculated quantities for the carotenoid molecules are analyzed. The orientation of the different carotenoid molecules in the monolayer is discussed.

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