Reaction in Monolayers at Liquid Surfaces

ELLIPSOMETRY The structure of liquid surfaces with monomolecular films can be studied by measuring the light reflected from the surface. The range of thickness that one generally considers to be measured varies from 100 to 1000 A (10-100 nm). However, in monolayers in which the molecules are oriented and the thickness involved is 5-50 A, the methods have been not easily pursued. In a differential method in which two beams of light from the same incandescent lamp were directed 

The technique of fluorescence spectral measurements has become very sensitive over the past decade. In order to obtain more information on the surface monolayers, a new method based on fluorescence was developed. It consisted of placing the monolayer trough on the stage of an epifluorescence microscope, with doped low concentration of fluorescent lipid probe. Later, ordered solid-liquid coexistence at the water-air interface and on solid substrates were reported. The theory of domain shapes has been extensively described by this method. 

The presence of lipid (or similar substance) monolayer at the surface of the aqueous phase gives rise to many changes in the properties at the interface. The major effects that have been investigated extensively are 

There are also other surface properties that change, and these will be described later (Chapter 4.4). 

A monomolecular film is resistant to shear stress in the plane of the surface, as is also the case in the bulk phase a liquid is retarded in its flow by viscous forces. The viscosity of the monolayer may indeed be measured in two dimensions by flow through a canal on a surface or by its drag on a ring in the surface, corresponding to the Ostwald and Couette instruments for the study of bulk viscosities. The surface viscosity, r s, is defined by the relation 

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