Interface size effects

The onset of flow instability in a heated capillary with vaporizing meniscus is considered in Chap 11. The behavior of a vapor/liquid system undergoing small perturbations is analyzed by linear approximation, in the frame work of a onedimensional model of capillary flow with a distinct interface. The effect of the physical properties of both phases, the wall heat flux and the capillary sizes on the flow stability is studied. A scenario of a possible process at small and moderate Peclet number is considered. The boundaries of stability separating the domains of stable and unstable flow are outlined and the values of the geometrical and operating parameters corresponding to the transition are estimated. 

K. B. Migler 2002, (Layered droplet microstructures in sheared emulsions finite-size effects), /. Colloid Interface Sci. 255, 391. 

The quantity G of the effective mixing mass flux is determined by the turbulent velocity fluctuations at the bubble-layer edge. The distance of the edge of the bubble layer from the wall is taken as the distance at which the size of the turbulent eddies is k times the average bubble diameter. Weisman and Pei have determined empirically that k equals 2.28. Only a fraction of the turbulent velocity fluctuations produced are assumed to be effective in reaching the wall. The effective velocity fluctuations are those in which the velocity exceeds the average velocity away from the wall produced by evaporation heat flux q"b. At the bubble layer-core interface, the effective mass flux to the wall is computed as... 

It is observed that indentations made with low loads on an indenter are smaller than expected from the sizes made with high loads. Thus the apparent hardness of a specimen increases as the indentation size decreases. This is known as the indentation size effect (ISE). It has been given a variety of interpretations, but the most simple is that it is associated with friction at the interface between the indenter and the specimen (Li et al., 1993). 

The susceptibility of hardness measurements of silica and silicate glasses to environmental factors is consistent with the effects of water on the deformation of quartz. The load effect and indentation size effect appear to be a result of the frictional forces at the indenter-specimen interfaces. 

In many catalytic systems, nanoscopic metallic particles are dispersed on ceramic supports and exhibit different stmctures and properties from bulk due to size effect and metal support interaction etc. For very small metal particles, particle size may influence both geometric and electronic structures. For example, gold particles may undergo a metal-semiconductor transition at the size of about 3.5 nm and become active in CO oxidation [10]. Lattice contractions have been observed in metals such as Pt and Pd, when the particle size is smaller than 2-3 nm [11, 12]. Metal support interaction may have drastic effects on the chemisorptive properties of the metal phase [13-15]. Therefore the stmctural features such as particles size and shape, surface stmcture and configuration of metal-substrate interface are of great importance since these features influence the electronic stmctures and hence the catalytic activities. Particle shapes and size distributions of supported metal catalysts were extensively studied by TEM [16-19]. Surface stmctures such as facets and steps were observed by high-resolution surface profile imaging [20-23]. Metal support interaction and other behaviours under various environments were discussed at atomic scale based on the relevant stmctural information accessible by means of TEM [24-29]. 

Equation (5.1) describes the size effects associated with the presence of a finite nucleus and reflects the balance between bulk and surface contributions. The limiting case L 00 represents the ideal formation of a film under complete wetting. The convention is that the system evolves towards negative values of G. When G > 0 the interface term dominates over the bulk term (low L values) while the opposite situation is found for G < 0 (higher L values). Underthe condition 9G/9L = 0, Gc and the critical length of nucleation, are given by the expressions ... 

Guo CX, Boullanger P, Liu T, Jiang L. Size effect of polydiacetylene vesicles functionalized with glycolipids on their colorimetric detection ability. J Phys Chem B Condens Matter Mater Surf Interfaces Biophys 2005 109 18765-18771. 

Cations and anions with a strong solvation shell retain their solvation shell and thus interact with the electrode surface only through electrostatic forces. Since the interaction is exclusively electrostatic, the amount of these ions at the interface is defined by the electrostatic bias between the sample and the counter electrodes and independent from the chemical properties of the electrode surface non-specific adsorption. Considering the size effect of their hydration shell, these ions are able to approach the electrode to a distance limited by the size of the solvation shell of the ion. The center of these ions at a distance of closest approach defined by the size of the solvation shell is called the outer Helmholtz layer. The electrode surface and the outer Helmholtz layer have charges of equal magnitude but opposite sign, resulting in the formation of an equivalent of a plate condenser on a scale of a molecular layer. Helmholtz proposed such a plate condenser on such a molecular scale for the first time in the middle of the nineteenth century. 

The expected greater size of protein-polysaccharide complexes can reduce the diffusion rate of the adsorbing species towards the interface. This effect is especially important for small monomeric proteins. In addition, Ganzevles and co-workers (2006) have suggested that the diffusion of protein in the complexes may not solely be responsible for the slow surface tension decay. Rather, the gradual dissociation (and subsequent adsorption) of protein from complexes, when they are in close proximity to the interface, could also contribute to the behaviour. 

Finally we comment on the finite size effect due to the surface tension a at the gel-solvent interface. For a spherical gel with radius R, the equilibrium condition becomes... 

The ET rate between FeCp-X and Fe(III) across the TBP-droplet/water interface has been determined for individual microdroplets, and two classes of the droplet-size effect on the ET rate are found the A/V ratio effect (r > 5 /im) and the micrometer size effect r < 5 /mi). The findings at r < 5 /an are very important, since characteristic features of a spherical micro-liquid/liquid interface, different from a flat interface, have been observed experimentally. 

Analogous droplet-size dependence has been observed for electron transfer between ferrocene and hexacyanoferrate(III) across a droplet/water interface with the droplet radius of <5 /an, as described in Section III [80]. In this system, FeCp-X+ transfer is coupled with the electron transfer process and the physical properties of the droplet have been suggested to vary with r. However, droplet size effects on surface capillary waves analogous to those in the MT process may also govern the electron transfer process in the FeCp-X/Fe(IIl) system. 

The properties of immiscible polymers blends are strongly dependent on the morphology of the blend, with optimal mechanical properties only being obtained at a critical particle size for the dispersed phase. As the size of the dispersed phase is directly proportional to the interfacial tension between the components of the blend, there is much interest in interfacial tension modification. Copolymers, either preformed or formed in situ, can localize at the interface and effectively modify the interfacial tension of polymer blends. The incorporation of PDMS phases is desirable as a method to improve properties such as impact resistance, toughness, tensile strength, elongation at break, thermal stability and lubrication. 

Some of the commonly used techniques for measuring contact angle [215, 216, 217] are the sessile drop method, captive bubble method and Wilhelmy plate method. These techniques have been extensively used and well documented for characterisation of modified PE surfaces [218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230] for various applications. Whitesides et al. [231 ] studied the wetting of flame-treated polyethylene film having ionisable organic acids and bases at the polymer-water interface. The effect of the size of substituted alkyl groups in amide and ester moieties on the surface hydrophilicity was also studied [232]. The biocompatibility of the polyethylene film surface modified with various water-soluble polymers was evaluated using the same technique [233]. The surface properties of hy-perbranched polymers have been very recently reported [234]. 

Ferroelectric thin films considerably gain in interest within the last couple of years due to their potential application in nonvolatile random-accessmemory devices (FeRAM). Among potential candidates, PbZr. n i, (>> (pzt) is one of the most promising materials because of its large remanent polarization and low coercive field. However, pzt is also well known for its poor fatigue behavior on metal electrodes [1,2] and occurrence of size effects [3-5] which are well due to the ferroelectric/electrode interface properties [1-5]. 

Influence of the M/SCparticle size on its electronic structure (so-called size- effect). In classical M/SC particles, which determine the properties of PVD-produced composite films, this effect is caused by interaction of conductivity electrons with an interface between a particle and an environment. It results in occurrence of surface potentials and redistribution of electronic density in a particle. 

Kunitake and coworkers experimentally investigated the effect of interface size on molecular recognition efficiency with a guanidinium-phosphate interaction (Fig. 2.4). Binding constants of aqueous phosphates such as adenosine monophosphate (AMP) to a monolayer of a guanidinium amphiphile were determined to be in the range of 106... 

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