Media depleted layer

As we have discussed earlier in the context of surfaces and interfaces, the breaking of the inversion synnnetry strongly alters the SFIG from a centrosynnnetric medium. Surfaces and interfaces are not the only means of breaking the inversion synnnetry of a centrosynnnetric material. Another important perturbation is diat induced by (static) electric fields. Such electric fields may be applied externally or may arise internally from a depletion layer at the interface of a semiconductor or from a double-charge layer at the interface of a liquid. 

Figure 1. Schematic outline of the typical dimensions of the various physically relevant layers at the organism/medium interphase cell membrane, cell wall layer, electric double layer, diffusive depletion layer...

Figure 3.6 Effect of Ca2+ content on predicted values of osmotic pressure (H, , left axis) of caseinate nanoparticles in emulsion continuous phase and the free energy of the depletion interaction (AGdep, , right axis) between a pair of emulsion droplets (

The fact that the effective viscosity is intermediate between that of solvent and polymer solution can be rationalized as follows. Within the depletion layer, the viscosity is expected to follow the polymer density distribution [289] and it gradually increases from the solvent viscosity at the solid surface to the bulk viscosity far from the particle. Therefore, as a particle difliises, the hydrodynamic resistance force is also in between the two limits. Fan et al. [294, 295] derived analytical expressions for the friction felt by a sphere when it moves through a macromolecular medium, and showed that the friction is strongly reduced compared to Stokes law. This means that depletion-induced slip effects facilitate protein transport through crowded media. 

Figure 5.7 Schematic diagram illustrating depletion flocculation, (a) Two large spheres (radius a) separated by a surface. Surface distance h possesses a depletion layer (A) with a thickness of the order of the radius Rg of the nonadsorbed species (dashed circle), (b) Osmotic pressure of the external medium pushes the large spheres together in the directions of the arrows. For clarity, this diagram is not to scale the size ratio of large spheres to nonadsorbed species is typically considerably greater (Radford and Dickinson, 2004).

At temperatures of the order 700 - 900 K the surface point defects play the dominant role in controlling the various eledrophysical parameters of adsorbent on the content of ambient medium [32]. As it has been mentioned in section 1.6, these defects are being formed in the temperature domain in which the respective concentration of volume defects is very small. In fact, cooling an adsorbent down to room temperature results violation of uniform distribution due to redistribution of defects. The availability of non-homogeneous defect distribution led to creation of a new model of depleted surface layer based on the phenomenon of oxidation of surface defects [182] which is an alternative to existing model of the Shottky barrier [183]. 

The second expression in equation (44) implies that the bulk concentration in the medium is not affected by the consumption of i towards the particle, i.e. the overall depletion is insignificant. In case of the presence of an ensemble of bodies (or particles), this means that the distance between different bodies (or particles) is sufficiently large compared with the steady-state diffusion layer (i.e. the dispersion should be sufficiently diluted). 

Homogeneous, transparent solutions of proteins, carbohydrates, and other compounds can separate into two layers, one depleted and one enriched with these compounds. The process of separation of macromolecules into discrete entities is termed coacervation. The layer rich in molecules of the dissolved substance, referred to as the coacervate layer, actually consists of liquid "drops" or spherical microcapsules. The equilibrium liquid, which is the medium adjoining the coacervate layer, always contains less substance than the original solutions. The discrete liquid droplets resulting from macromolecular interactions might be made to serve as pseudocells from which pseudo tissues might be derived to constitute a restructured food. 

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