Mechanism interfacial phenomena

Several mechanisms have been proposed to explain reverse osmosis. According to the preferential sorption-capillary flow mechanism of Sourirajan [114], reverse osmosis separation is the combined result of an interfacial phenomenon and fluid transport under pressure through capillary pores. Figure 5.58a is a conceptual model of this mechanism for recovery of fresh water from aqueous salt solutions. The surface of the membrane in contact with the solution has a preferential sorption for water and/or preferential repulsion for the solute, while a continuous removal of the preferentially sorbed interfacial water, which is of a monomolecular nature, is effected by flow under pressure through the membrane capillaries. According to this model, the critical pore diameter for a maximum separation and permeability is equal to twice the thickness of the preferentially sorbed interfacial layer (Figure 5.58b). 

Interfacial behavior of different silicones was extensively studied, as indicated in Section 3.12.4.6. To add a few more examples, solution behavior of water-soluble polysiloxanes carrying different pendant hydrophilic groups, thus differing in hydrophobicity, was reported.584 A study of the aggregation phenomena of POSS in the presence of amphiphilic PDMS at the air/water interface was conducted in an attempt to elucidate nanofiller-aggregation mechanisms.585 An interesting phenomenon of the spontaneous formation of stable microtopographical surface domains, composed primarily of PDMS surrounded by polyurethane matrix, was observed in the synthesis of a cross-linked PDMS-polyurethane films.586... 

The mechanism governing the formation of interply bonds has been established as autohesion or self-diffusion [28], Autohesive bonding is controlled by two mechanisms (1) intimate contact between the interfacial surfaces, and (2) diffusion of the macromolecules across the interface. Figure 7.22 shows the phenomenon of autohesion for an amorphous thermoplastic polymer. At time zero, the two surfaces are pressed together. Providing the temperature is... 

It is a common phenomenon that the intercalated-exfoliated clay coexists in the bulk and in the interface of a blend. Previous studies of polymer blend-clay systems usually show that the clay resides either at the interface [81] or in the bulk [82]. The simultaneous existence of clay layers in the interface and bulk allows two functions to be attributed to the nanoclay particles one as a compatibilizer because the clays are being accumulated at the interface, and the other as a nanofiller that can reinforce the rubber polymer and subsequently improve the mechanical properties of the compound. The firm existence of the exfoliated clay layers and an interconnected chain-like structure at the interface of CR and EPDM (as evident from Fig. 42a, b) surely affects the interfacial energy between CR and EPDM, and these arrangements seem to enhance the compatibility between the two rubbers. 

Locus of failure studies 75 80) on metal/epoxy joints that had been exposed to water indicate that corrosion of the metal substrate does not occur until after interfacial failure has occurred. This suggests that corrosion itself does not play a primary role in the loss of adhesion strength mechanism of metal/epoxy joints, but rather is a post-failure phenomenon. However, for the case of metal/epoxy protective coating systems, Leidheiser and coworkers 88-91 -92) and Dickie and coworkers 5 87-89-90> have proposed that localized corrosion processes are part of an important delamination mechanism. 

Z3. PMDA-ODA on MgO. PMDA-ODA peel force data shown in Fig. 7 exhibit a very interesting phenomenon as a function of T H exposure. The peel force is significantly increased as the time in T H is increased. This is somewhat unusual, but apparently repeatable. The exposure to APS has not made much difference in the results, which is understandable from the initial surface analyses after IPA cleaning and APS exposure. The XPS data show no detectable amount of APS on the thus exposed MgO surface. The reasons for the peel force increase as a function of T H exposure are not clear at this time. This is, however, due to increased interfacial strength, and not due to the polyimide mechanical properties (Young s modulus and yield stress) changes. If the latter were the case, then we should see similar effects also in the first two cases, which is not seen. However, more detailed analysis is essential to clarify the exact mechanism and this observation merits further study. 

Thus, protein adsorption and cell adhesion occur for various reasons and in different appearances. When surfaces of living systems are involved, specific recognition mechanisms undoubtedly play crucial roles. Nevertheless, since we are dealing with a rather general phenomenon, it is likely that these specific interactions are superimposed on a generic interaction mechanism. Bioadhesion and adsorption is very complicated from a physical chemical point of view. Interfacial tensions, wetting and electrical properties of the surfaces are prominently involved. 

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