Molecular mechanics deformations, structure

The presented results and the additional information taken from various references indicate the direct relevance of the size of the network strands for the crack opening displacement and consequently for the toughness of the polymer. In polymers under load, the molecular chains at the tip of the crack break after the deformation zone ahead of the crack has grown to a critical width 5C, that is the crack opening displacement. This value 5C is proportional to the length of the molecular strands of the network and is linked in this way to the molecular structure of the polymer. However, the molecular mechanism for chain breakage in the deformation zone is not known at present. 

If the ordered, crystalline regions are cross sections of bundles of chains and the chains go from one bundle to the next (although not necessarily in the same plane), this is the older fringe-micelle model. If the emerging chains repeatedly fold buck and reenter the same bundle in this or a different plane, this is the folded-chain model. In either case the mechanical deformation behavior of such complex structures is varied and difficult to unravel unambiguously on a molecular or microscopic scale. In many respects the behavior of crystalline polymers is like that of two-ph ise systems as predicted by the fringed-micelle- model illustrated in Figure 7, in which there is a distinct crystalline phase embedded in an amorphous phase (134). 

The molecular nature of the neuronal receptors is now becoming understood with the advent of molecular biological techniques. The molecular structure of the mechanosensitive channels has been established only recently. In principle mechanosensitive channels must be opened by mechanical deformation of the neural membrane in which they are em-... 

An area of increasing interest is the selective complexation of Sn2+ and more particularly Pb2+ for the treatment of heavy metal poisoning. Molecular mechanics has been extensively applied to the problem of metal ion selectivity (see Chapter 8) but there have been few studies of lead or tin complexes. The fit of Sn2+ to 18-crown-6 has been considered12811, as has the size selectivity of tetraazamacrocycles with respect to Pb2+ binding131. The binding of Pb2+ to porphyrin-1 has been modeled, though in this case the point of interest was the structural deformations caused by the metal cation11901. 

As a single cell technique capable of achieving large deformations, the method complements the pressure probe method. It should be valuable in studies of how plant cell mechanical properties are affected by the molecular composition and structure of the wall, and how these are affected by food processing operations. 

For angle deformation, by analogy, Vg = k A6), etc. This assumption is clearly valid only for small displacements and cannot be used to model the rupture of a chemical bond. A Morse potential would be more appropriate in such application. To model the formation of a bond, an even more complicated potential, that takes activation effects into account, is required. However, most applications, known as molecular mechanics are less ambitious and have as their final objective only the modelling of the three-dimensional molecular structure. It assumes that the strain in a molecule is made up of the sums for various modes of distortion, e.g. ... 

On the basis of the SANS results, a molecular mechanism has been recently proposed for the toughness enhancement of DN gels [34]. This mechanism rationalizes the changes in molecular structure of the DN gel constituents observed via in-situ neutron scattering measurements, the composition dependence of the solution viscosity, and the thermodynamic interaction parameters of PAMPS and PAAm molecules obtained previously from neutron scattering studies. More specifically, this proposed mechanism provides an explanation for the observed periodic compositional fluctuations in the micrometer range induced by large strain deformation. 

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