Autophobic liquids

Table VII. Some Autophobic Liquids and Their Contact Angles on High-Energy Surfaces [54]...

In addition to overcoming experimental difficulties, the Naval Research Laboratory group has contributed many important generalizations and new concepts-for example, the concepts of low energy solid [33,69], critical surface tension [33,61], and autophobic liquid [32,41]. These developments have also stimulated the search for an interpretative scheme capable of yielding values of solid-vapor and solid-liquid interfacial tensions. 

Timmons, C. O., Zisman, W. A., "A Study of Autophobic Liquids on Platinum by the Contact Potential Method," Naval Research Lab., NRL Rept. 6020 (1963). 

AUTOPHOBIC LIQUIDS AND THE PROPERTIES OF THEIR ADSORBED FILMS. 

Hare, EF. and Zisman, W.A., Autophobic liquids and the properties of their adsorbed films, J. Phys. Chem., 59, 335, 1955. 

Kahn et al, also noted that the 7c of a solid, in particular one of high surface energy, can be drastically lowered by the presence of a layer of liquid molecules that has been preferentially adsorbed at the solid-liquid interface. If the molecules in the monolayer have both polar and nonpolar ends, the polar ends will often attach themselves to the high-energy surface, with the nonpolar portion facing into the liquid. As far as the bulk liquid is concerned, the nonpolar groups present a lower surface energy to the fluid than the free solid surface, and consequently the effective 7c is lowered. The adsorbed mono-layer can consist of intentionally added impurities in the fluid " or unintentional impurities. In addition, for certain impurity-free liquids, the molecular structure may be such that the fluid cannot spread on its own monolayer. These are known as autophobic liquids. 

C. Liquid-Surface Interactions Surface Changes and Autophobicity... 

When a surface-active agent is present in a liquid droplet, it can adsorb to the surface, lower the surface energy, and cause the liquid contact angle to increase. This phenomenon, known as autophobicity, was postulated by Zisman many years ago [78, 79]. Autophobicity is quite striking in wetting films on clean... 

The observation of liquid drops on top of a film of the same substance is often referred to as pseudo-partial [ 1 ] or autophobic wetting. This behavior is not surprising in this... 

Another explanation has been offered for the observed maximum in spreading area with concentration, based on the concept of autophobicity, i.e., the existence of an adsorbed layer of surfactant at the liquid-solid interface that is not wetted by its own kind [44]. However, the short time scale of the spreading ( 2 seconds in the high concentration regime) requires that this autophobic layer is laid down in this short period, which is unlikely considering the kinetic limitations on reorientation of molecules [50]. 

Therefore, the inverse gas chromatography method allows us to determine the model of long-chain aliphatic alcohol distribution on the surface of porous silica gel if the amount of alcohol on adsorbent surface is equal or exceeds the monolayer capacity, then the monolayer is composed of alcohol molecules oriented their polar moieties to the adsorbent surface. The monolayer, in a solid-condensed state, is stable up to 81°C. At this temperature the monolayer transfers into a liquid-expanded state. The threedimensional excess of alcohol, because the autophobicity phenomenon, does not wet the monolayer surface. 

FIGURE 17.8. An interesting phenomenon sometimes encountered in spreading is the autophobic effect. When the liquid is first applied to the surface, it has a small contact angle however, as adsorption occurs at the solid-liquid interface, the orientation of the adsorbed molecules makes the interface more hydrophobic, leading to a larger contact angle. 

In 1955, Fox, Hare, and Zisman published the generalization that all pure liquids spread spontaneously on high-energy surfaces unless the liquid is (a) "autophobic or (b) is able to decompose on adsorption to release a more adsorbable product which converts the solid surface into one of low-surface energy. ... 

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