Surface Phase Transitions at Liquid-Mixture/Solid Interfaces

Abstract

In an adsorption study from a liquid mixture, the choice of a moderately hydrophilic silica and of a solute like 2,5-dimethylpyridine (2,5-DMP), known for its layering ability in dilute solution in water, allows the observation of several adsorption gaps on the isotherms established at different temperatures. These gaps may be attributed to surface phase transitions. Collected on a (T-Γ21) diagram, they constitute a surface phase diagram highly similar to the bulk water-2,5 DMP liquid-solid diagram at low temperature. It is the first example of a surface phase diagram at a liquid-mixture/solid interface.

Surface Phase Diagrams: Evidence of Molecular Arrangements at the Aqueous-Solution/Solid Interface

“…It suggests the presence of solid solutions on the surface. 13 The equivalent in the bulk is schematized in Figure 8. Generalization about our first observation is quite satisfactory and, as already pointed out, brings to the forefront a very interesting view of the surface behavior in this kind of system.…”

“…This gave us information about the nature of the surface phase and allowed us to supplement and generalize our previous results obtained on the water (W)-2,5DMP-Aerosil 200 system. 13 Here, we also give the liquid-liquid bulk phase diagram of this mixture which is very similar to the 2,6DMP-water one. [51][52][53] This dual set of phase diagrams, both in the surface and in the bulk, is absolutely unique because no alike combination of data is available in the literature.…”

“…Surface (two-dimensional) phase transitions were early observed by means of surface pressure variations in the so-called Langmuir films, [1][2][3][4] but this was long after the existence of surface films had been proven and used; 5 they also exist at the solid surface in contact with an infinite fluid reservoir. [6][7][8][9][10][11][12][13] Other studies have also identified them with the so-called "prewetting transition". [14][15][16][17][18][19][20][21][22][23][24][25][26][27] According to Cahn 14 and all the theorists cited hereafter, such a prewetting transition is associated with critical points in the bulk as well as in the surface and then falls within fluid-fluid transitions.…”

Critical Point Corrections for Two- and Three-Dimensional Systems

“…Modeling phase behavior of fluids at interfaces − is necessary to understand molecular mechanisms of surface tension in liquids and adsorption behavior at surfaces and interfaces. , Important features of interfaces include density gradients and oscillatory density profiles near the surfaces of liquids − and the interrelationship between two- and three-dimensional behaviors. − The role of dimensionality is not limited to geometry of the system but also includes correlation effects on heterogeneous surfaces , and in nanopores. − Dimensionality also affects critical phenomena including long-range critical fluctuations and universal scaling laws…”

Adsorption of Amphiphilic Dimers at Surfaces

“…An important type of self-assembly is the adsorption of amphiphiles at surfaces (16)(17)(18). The differences in sizes of molecules can be taken into account by considering chain molecules (19,20).…”