Interfacial mechanism diffusion theory

The development of interfacial contact is the mechanism proposed for auto-hesion in a series of papers by Anand and his collaborators [90-94] and a summary of Anand s objections to Voyutskii s diffusion theory has also been published [95]. Anand makes the significant point that the instantaneous autohe-sive strength exceeds zero. 

Although the mechanisms of polyimide/metal adhesion remain to be fundamentally elucidated, it is generally accepted that the interfacial diffusion of metallic entities into the polyamic acid plays a key role at the interface [156-158]. Two main theories have been reported explaining the adhesion of the Pl/metal bond chemical and mechanical bonding [159]. Initial work emphasized mechanical bonding and most efforts were dedicated to the physical roughening of the substrate by different abrasive methods as well as chemical treatments in order to improve metal to polyimide adhesion by increasing the metal surface area [156,160-164]. 

The result obtained from the film theory is that the mass transfer coefficient is directly proportional to the diffusion coefficient. However, the experimental mass transfer data available in the literature [6], for gas-liquid interfaces, indicate that the mass transfer coefficient should rather be proportional with the square root of the diffusion coefficient. Therefore, in many situations the film theory doesn t give a sufficient picture of the mass transfer processes at the interfaces. Furthermore, the mass transfer coefficient dependencies upon variables like fluid viscosity and velocity are not well understood. These dependencies are thus often lumped into the correlations for the film thickness, 1. The film theory is inaccurate for most physical systems, but it is still a simple and useful method that is widely used calculating the interfacial mass transfer fluxes. It is also very useful for analysis of mass transfer with chemical reaction, as the physical mechanisms involved are very complex and the more sophisticated theories do not provide significantly better estimates of the fluxes. Even for the description of many multicomponent systems, the simplicity of the model can be an important advantage. 

The self-adhesion (autohesion) of polymers is of considerable practical importance as many moulding operations involve the need for streams of merging polymer melt to self-adhere to form a strong bond necessary to the integrity of the moulded article. Mechanisms of polymer diffusion are discussed in Polymer diffusion reptation and interdigitation and theories that relate interfacial structure to strength in Polymer-polymer adhesion models. In the latter article, the vector percolation (VP) model was described, which is here applied to welding, and the practical consequences of its predictions are drawn out. - ... 

Processes involving water transport and transformation. What are the relevant mechanisms and transport coefficients of water fluxes (diffusion, convection, hydraulic permeation, electroosmotic drag) What are relevant mechanisms and rates of phase changes (between liquid water, water vapor, surface water, water in membrane) These mechanisms and relevant parameters are amenable to evaluation by ex situ diagnostics. The statistical theory of random composite media [136-138] and percolation theory [44-46] provides various tools for assessing effective parameters of transport and interfacial processes, as discussed in Section 8.4. 

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