Interfacial diffusion

Then, a concentration gradient of hj lrated redox particles arises in the interfacial diffusion layer and the Fermi level EnitEix ). of redox particles at the interface becomes different from the Fermi level ensEDox) of redox particles outside the diffusion layer as shown in Fig. 8-9(c). The partial overvoltages t]h and iidiff are then given by Eqn. 8-32 ... 

Fig. 5.1 Interfacial diffusion films. 5 and 5 are the thickness of the organic and aqueous films, respectively. The presence of an adsorbed layer of extractant molecules at the interface is also shown.

The description of the diffusion films as completely stagnant layers, having definite and well-identified thicknesses, represents only a practical approximation useful for a simple mathematical description of interfacial diffusion. A... 

The interfacial diffusion model of Scott, Tung, and Drickamer is somewhat open to criticism in that it does not take into account the finite thickness of the interface. This objection led Auer and Murbach (A4) to consider a three-region model for the diffusion between two immiscible phases, the third region being an interface of finite thickness. These authors have solved the diffusion equations for their model for several special cases their solutions should be of interest in future analysis of interphase mass transfer experiments. 

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]. 

Table 6.2 Interfacial diffusion rates of acetone (1) and benzene (2) at the top of the column in Example 6.3...

Chemical reaction kinetics depends on the thermal fluctuation and diffusion of all reactants and solvent molecules. In addition, the specific reaction kinetics at the liq-uid/liquid interface must be considered. The diffusion to the interface and the diffusion within the interface are important processes in determining the reaction rate at the interface. Several aspects of interfacial diffusion and the rotational motion of the interfacially adsorbed molecules are introduced here as results of recent studies. 

The influence of internal and interfacial diffusion on catalyst deactivation by simultaneous sintering and poisoning is examined. The study focuses on the copper catalyst used in the water gas shift reaction ( WGSR). It is found that catalyst life increases when internal and external poison diffusional resistance increases. Temperature reduces the total average activity but this effect is partially neutralized by the diffusional effects undergone by the reactants inside the pellet. 

The aim of this work is to analyze the effect of internal and interfacial diffusion on a catalyst pellet in the presence of an activity decay by simultaneous poisoning and sintering. The study has been applied to a copper based catalyst used in the WGSR CO + H2O = CO2 + H2, for which a Langmuir-Hinshelwood type kinetics has been considered [2]. 

Klinger, L. Rabkin, E. Theory of nanoindentation creep controlled by interfacial diffusion. Scripta Mater. 2003, 48, 1475-1481. 

Although this chapter has focused on phase transfer reactions at solid/ liquid interfaces, many of the techniques and principles are generally applicable to such processes at liquid/liquid and air/liquid interfaces. Studies of adsorption/desorption, absorption, dissolution, and lateral interfacial diffusion at these types of interface are of considerable fundamental and practical importance, and SECM studies in these areas are already appearing. 

In another approach, the interfacial diffusion of the nanoparticles was determined using two photobleaching methods fluorescence loss induced by photobleaching (FLIP) and fluorescence recovery after photobleaching (FRAP). It was found that the lateral diffusion of the nanoparticles at the interface as well as the diffusion normal to and from the interface deviated by about four orders of magnitude from the values obtained in free solution [46],... 

In technological applications as well as in scientific experiments specific boundary conditions are often given, such as definite changes of the interfacial area. A schematic representation is given in Fig. 4.2. which shows various bulk and interfacial transport processes of surface active molecules diffusion in the bulk, interfacial diffusion, bulk flow of different origin, interfacial compression and dilation. 

FIGURE 12.12. Idealised interfacial diffusion after a period of time... 

Interfacial Diffusion of Fluids in Pressure Sensitive Adhesives... 

This work suggests that these novel sensors are applicable for the study of interfacial diffusion processes, and could be extended to other coatings or adhesives in a variety of environments. 

Measurements of the electrical response of polymer materials has been used to elucidate molecular relaxations [1], monitor real-time changes in the chemical and physical state in polymers brought about by crystallization [2] and cure [3], measure moisture diffusion into polymers [4], and measure the moisture content and integrity of adhesive joints [5-8]. Our research applies this technique in order to obtain detailed measurements of interfacial diffusion of fluids into an adhesive bondline. 

Bulk diffusion into adhesive Joints has been studied considerably [9], however little work has focused on diffusion at adhesive interfaces, largely because of the limitations of experimental techniques. Mass uptake experiments are a convenient method to study fluid absorption in adhesives. This method has been used to study interfacial diffusion by comparing the relative rates of diffusion from non-bonded or free-standing films with diffusion into the actual adhesive joint [10,11]. A disadvantage of mass uptake experiments is that the method does not provide any direct evidence of the concentration of fluid at the interface. 

Our research builds on this limited body of work concerning diffusion at the interface of adhesive joints. We have measured the interfacial diffusion process of acetone into a bonded pressure sensitive adhesive tape bj employing single frequency capacitance measurements and a novel interdigitated electrode sensor design. 

The absorption of acetone at room temperature into an adhered PSA tape was measured by applying the technique of SFCM and utilizing a unique interdigitated electrode sensor design. The interfacial diffusion results and adhesion measurements were compared, and the relationship between the relative concentration and adhesion loss was determined. This study suggests these novel sensors are applicable for the study of interfacial diffusion processes, and could be extended to other coatings or adhesives in a variety of environments. 

These two models illustrate how the properties of the compound influence the rate of evaporation from water under static conditions. Environmental conditions such as wind speed and turbulence in the water phase will have a marked influence on rates of evaporation that would reduce gradients and also reduce the width of the interfacial diffusion layers and systematic analysis of these effects have been discussed. Other variables will affect evaporation rates by controlling the actual concentration of the compound in solution. Suspended sediments and/or DOM would act in this manner. Weak acids and bases would only evaporate as the neutral species since the complementary anions or cations would be more water soluble and essentially have no vapor pressure. Consequently, environmental pH relative to pA values will be a consideration. It should be mentioned that compounds may distribute into the vapor phase by other processes than evaporation. Formation of aerosols, for example, can be a factor. 

Fig. 31.2 Measurement of the interfacial diffusion of hydrated ions by means of the scanning Kelvin probe on a polished iron substrate (purity 99.99%) coated with an adhesive layer about 70 pm thick (hot-curing, two-component epoxy resin adhesive with amine-based hardener) containing an aminosi-lane adhesion promoter (3-(tri-methoxysilyl) propylamine).

The approach of two droplets under the capillary pressure acting normal to the interface causes liquid to be squeezed out of the film into the bulk. This liquid flow results in the convective flux of surfactant in the sublayer. Therefore, the surfactant concentration at the interface is increased in the direction of that flow. The other fluxes associated with the drainage process shown include (1) bulk flux in the droplet, (2) bulk flux in the film phase, and (3) interfacial diffusion flux caused by the concentration gradient at the interface [15,18,22,37-39]. 

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