Structure, interface

Figure A3.3.8 Interface structure for i = 5000, = 0. In (a) the shaded regions correspond to interfaces...

Wool, R.P., Polymer Interfaces, Structure and Strength. Hanser Publishers, Munich, 1995. Ishida, H. In Akovali, G. (Ed.), The Interfacial Interactions in Polymeric Composites. Kluwer Academic, Dordrecht, 1993, p. 169. 

The interdiffusion of polymer chains occurs by two basic processes. When the joint is first made chain loops between entanglements cross the interface but this motion is restricted by the entanglements and independent of molecular weight. Whole chains also start to cross the interface by reptation, but this is a rather slower process and requires that the diffusion of the chain across the interface is led by a chain end. The initial rate of this process is thus strongly influenced by the distribution of the chain ends close to the interface. Although these diffusion processes are fairly well understood, it is clear from the discussion above on immiscible polymers that the relationships between the failure stress of the interface and the interface structure are less understood. The most common assumptions used have been that the interface can bear a stress that is either proportional to the length of chain that has reptated across the interface or proportional to some measure of the density of cross interface entanglements or loops. Each of these criteria can be used with the micro-mechanical models but it is unclear which, if either, assumption is correct. 

Wool, R.R, Polymer Interfaces Structure and Strength. Hanser Gardner, Cincinnati, OH, 1995. 

The development of the relation between interface structure and strength is suggested to proceed as follows ... 

When relating interface structure to strength, the literature is replete with analyses, which are based on the nail solution [1,58], as shown in Fig. 10. This model is excellent when applied to very weak interfaces (Gic 1 J/m ) where most of the fracture events in the interface occur on a well-defined 2D plane. However, the nail solution is not applicable to strong interfaces (Gic 100-1000 J/m ), where the fracture events occur in a 3D deformation zone, at the crack tip. In Fig. 10, two beams are bonded by E nails per unit area of penetration length L. The fracture energy G c, to pull the beams apart at velocity V is determined by... 

The molecular aspects of. interdiffusion of linear entangled polymers M > Mc cmi fng elcffft g (S pofymer interfaces are summarized in Table 1 [1]. The regJt tion( i qraiq piS 1the interface structure relations in Table 1 hav gbp p... 

Here r is the distance between the centers of two atoms in dimensionless units r = R/a, where R is the actual distance and a defines the effective range of the potential. Uq sets the energy scale of the pair-interaction. A number of crystal growth processes have been investigated by this type of potential, for example [28-31]. An alternative way of calculating solid-liquid interface structures on an atomic level is via classical density-functional methods [32,33]. 

Typical surfaces observed in Ising model simulations are illustrated in Fig. 2. The size and extent of adatom and vacancy clusters increases with the temperature. Above a transition temperature (T. 62 for the surface illustrated), the clusters percolate. That is, some of the clusters link up to produce a connected network over the entire surface. Above Tj, crystal growth can proceed without two-dimensional nucleation, since large clusters are an inherent part of the interface structure. Finite growth rates are expected at arbitrarily small values of the supersaturation. 

We can distinguish between the interface structure of the nucleus, N, and the crystal being transformed, A. This can be seen in the following diagram ... 

It is therefore not surprising that the interface structure has a large effect... 

These equations allow us to calculate both numbers of embryos being formed and the energy involved in their formation. Thus, the interface structure affects the rate of nuclei formed and the rate of transformation... 

Z. Koczorowski, in The Interface Structure and Electrochemical Processes at the Boundary Between Two Immiscible Liquids, Ed. by V. E. Kazarinov, Springer Verlag, Berlin, 1987,pp, 77-106. 

Figure 5.2 Schematic models of different solid/gas interface structures.

Food typically is a complicated system with diverse interfaces. Stable air-water or oil-water interfaces are essential for the production of food foams and emulsions. Interface phenomena, therefore, attract great interest in the food industry. AFM provides enough resolution to visualize the interface structures, but it cannot be directly applied on air-liquid or liquid-liquid interfaces. Fortunately, the interface structure can be captured and transferred onto a freshly cleaved mica substrate using Langmuir-Blodgett techniques for AFM scan. Images are normally captured under butanol to reduce adhesion between the probe and the sample. Then, sample distortion or damage can be avoided (Morris et al, 1999). 

It is emphasized that revealing the dynamics as well as the structure (or conformation) based on several types of spin-relaxation times is undoubtedly a unique and indispensable means, only available from NMR techniques at ambient temperature of physiological significance. Usually, the structure data themselves are available also from X-ray diffraction studies in a more refined manner. Indeed, better structural data can be obtained at lower temperature by preventing the unnecessary molecular fluctuations, which are major subjects in this chapter, since structural data can be seriously deteriorated for domains where dynamics are predominant even in the 2D or 3D crystalline state or proteoliposome at ambient temperature. It should be also taken into account that the solubilization of membrane proteins in detergents is an alternative means to study structure in solution NMR. However, it is not always able faithfully to mimick the biomembrane environment, because the interface structure is not always the same between the bilayer and detergent system. This typically occurs in the case of PLC-81(1-140) described in Section 4.2.4 and other types of peptide systems. 

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