Kinetics of spreading

We better understand the kinetics of spreading and the histological processes of destruction of the different ocular tissues. The pathophysiology of chemical lesions, in case of an ocular bum, wiU be strongly illustrated, thanks to new technologies which can bring the experimental evidence of the theories developed in the following chapters. 

Non-equilibrium liquid films formed in the process of spreading have been considered in some early works, especially in the test of the theory of interfacial tension and the rule of Antonov [204], A review on the rule of Antonov and its interpretation on the basis of isotherms of disjoining pressure in wetting films is presented in [532]. However, these works do not deal with precise measurement of film thickness and the studies confined only the kinetics of spreading and lens formation. 

Fig. 111-28. The kinetics of spreading of a mercury drop on surfaces of zinc and lead [29]...

So long as the spreading coefficient is positive, the liquid will spread spontaneously. However, S y sy. is only a measure of the driving force for spreading and says nothing about the spreading rate or the ultimate state of equilibrium. We will deal with the kinetics of spreading in the next section. 

Lau, WWY. and Burns, C.M., Kinetics of spreading. Polystyrene melts on plane glass surfaces, J. Colloid Interface Sci, 45, 295, 1973. 

A more detailed analysis of the kinetics of spreading on the graphite surface shall be reported in a future paper [23]. 

The importance of kinetics of spreading has also been stressed by Bascom and Patrick. 

The emergence offerees of molecular interactions responsible for adhesion is possible only under conditions under which the molecular contact occurs at the adhesive-substrate interface. This process is dependent on the physical relief of the surface. The process of the formation of adhesive joints also depends on the kinetics of spreading, which, in turn, depends on the rheological properties of adhesive. As we have already noted, the state of true thermodynamic equilibrium in many cases cannot be achieved. 

It is obvious that the same forces are equally important in the kinetics of spreading. In this chapter we consider separately two cases that are drastically different the complete wetting that we begin with and then the partial wetting. The discussion in this chapter shows that, in the case of spreading, the whole drop profile should be divided into a number of regions, which are briefly discussed below. 

For a long time the so-called singularity on a three-phase contact Une [1] has been considered as a major problem in the consideration of the kinetics of spreading. We explain in the following text the source of this singularity and why it is removed by the disjoining pressure acting in a vicinity of the apparent three-phase contact line. 

Considerable experimental and theoretical material dealing with the spreading of droplets over a solid, nondeformable, dry surface has been accumulated for decades [10-13]. In the following text we present a derivation of equations that describe the kinetics of spreading in different situations. 

QUASI-STEADY-STATE APPROACH TO THE KINETICS OF SPREADING... 

In this chapter, we consider the kinetics of spreading over porous substrates. This phenomenon is widely used in the industry printing, painting, imbibition into soils, health care, and home care products, and so on. However, it is only recently that this process started to develop on a theoretical and not just on a purely empirical basis. 

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