Diffusion coatings continued mechanism

The transfer rate in the mixed side-pore model is proportional to the difference in concentration between the flowing-water and immobile-water phases. The transfer-rate constant kgA is a characteristic-rate parameter for diffusion in the immobile-water phase. Without the Freundlich sorption mechanism, this third model is the same as the dead-end pore model developed by Coats and Smith (19). The Freundlich sorption isotherm was included by van Genuchten and Wierenga (18) in their study, but they solved for the linear case only. Grove and Stollenwerk (20) described a similar model but included Langmuir sorption and a continuous immobile-water film phase. 

Thus, when investigating the nature and mechanism of adhesion between an adhesive, coating or polymer matrix and the substrate, it is important to consider the possibility of primary bond formation in addition to the interactions that may occur as a result of Dispersion forces and Poiar forces. In addition to the Adsorption theory of adhesion, adhesion interactions can sometimes be described by the Diffusion theory of adhesion, Electrostatic theory of adhesion, or Mechanical theory of adhesion. Recent work has addressed the formation of primary bonding at the interface as a feature that is desirable from a durability point of view and a phenomenon that one should aim to design into an interface. The concept of engineering the interface in such a way is relatively new, but as adhesives become more widely used in evermore demanding applications, and the performance XPS and ToF-SIMS systems continues to increase, it is anticipated that such investigations can only become more popular. 

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