Deformation individual molecule

Olovsson and coworkers have pointed out that the superposition of the electron density of adjacent molecules in the experimental deformation density may lead to modification of the contours in the lone-pair region of the water molecules (Fernandes et al. 1990, McIntyre et al. 1990). To avoid this complication, it is preferable to partition the crystal density through the multipole analysis, after which comparisons can be based on individual molecule or fragment densities. 

Bates 1984 Fredrickson and Larson 1987 Fredrickson andFIelfand 1988). The relaxation of these fluctuations involves collective motion of many molecules, and thus it is slower than the relaxation time of individual molecules. In small-amplitude oscillatory shearing, the fluctuation waveform is deformed, producing a slowly relaxing stress. Presumably, this accounts for (a) the anomalous contribution to G and (b) a similar, but smaller, contribution to G" (Rosedale and Bates 1990 Jin and Lodge 1997). (Similar anomalies are observed in polymer blends.) An asymmetric version of this PEP-PEE polymer that forms cylindrical domains shows an even larger low-frequency anomaly (Almdal et al. 1992). 

One-dimensional chains may be formed by inorganic materials either as stacks of individual molecules or as covalently bonded polymers. Emphasis is given to the former approach as these complexes are presently better characterized. It may also be possible to generate systems with one-dimensional properties through plastic deformation of normally three-dimensional materials (135,444). This class of materials is not yet widely characterized and is not discussed further. 

It has to do with whether the small deformation that we have been talking about depends on the energy eigenvalue speetrum of the individual molecules. 

SEM. Individual atoms and molecules cannot be used to provide satisfactory explanations of structural and especially fracture phenomena as they are neither deformed individually nor destroyed. Failure processes therefore need to he explained in terms of the behavior of the superstructures. 

Small-angle neutron scattering (SANS) of labelled (deuterated) amorphous samples and rubber samples detects the size of the coiled molecules and the response of individual molecules to macroscopic deformation and swelling. It has been shown that uncrosslinked bulk amorphous polymers consist of molecules with dimensions similar to those of theta solvents in accordance with the Flory theorem (Chapter 2). Fernandez et al (1984) showed that chemical crosslinking does not appreciably change the dimensions of the molecules. Data on various deformed network polymers indicate that the individual chain segments deform much less than the affine network model predicts and that most of the data are in accordance with the phantom network model. However, defmite SANS data that will tell which of the affine network model and the phantom network model is correct are still not available. 

The computational requirements of a molecular dynamics model can be greatly reduced if we make use of averaging to produce a mean-field model such as those based on the concept of a molecule in a tube. Here, instead of starting from a detailed picture of the interactions between individual molecules, we focus attention on a single molecule, a test chain, and represent the effect of all the surrounding molecules by an average field of constraints. Such models can be used to calculate the response to homogeneous deformations such as step shear and steady-simple shear. 

As reviewed thermoplastics (TPs) being viscoelastic materials respond to induced stress by two mechanisms viscous flow and elastic deformation. Viscous flow ultimately dissipates the applied mechanical energy as frictional heat and results in permanent material deformation. Elastic deformation stores the applied mechanical energy as completely recoverable material deformation. The extent to which one or the other of these mechanisms dominates the overall response of the material is determined by the temperature and by the duration and magnitude of the stress or strain. The higher the temperature, the most freedom of movement of the individual plastic molecules that comprise the... 

The first-formed individual atoms (ions or molecules) of B cannot be regarded as a distinct and separate phase but initially, at least, are expected to tend to conform to the structure of, and retain their former positions with reference to, the reactant phase A. During the continued accumulation of atoms (ions or molecules) of B, the consequent increase in total deformation strain energy will lead to a transformation to the structure characteristic of the stable product, solid B. This is quantitatively expressed [28] as a change in free energy by... 

Heavily crosslinked polymers, by contrast, tend to be very brittle and, unlike thermoplastics, this brittleness cannot be altered much by heahng. Heavily crosslinked materials have a dense three-dimensional network of covalent bonds in them, with little freedom for motion by the individual segments of the molecules involved in such structures. Hence there is no mechanism available to allow the material to take up the stress, with the result that it fails catastrophically at a given load with minimal deformation. 

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