Polymers dilatation process

Within the fi-ameworks of the cluster model [55] it has been assumed, that the segment joined to cluster means fluctuation fi-ee volume microvoid shrinkage and vice versa. In this case the microvoids number AA/j, forming in polymer dilation process, should be approximately equal to segments number AN subjected to partial melting process. These parameters can be estimated by following methods. The value AN is equal to [51] ... 

Two mechanisms of yielding may be distinguished in polymers diear yielding, which occurs essentially at constant volume, and crazing, which is a dilatation process. There are important differences between the two mechanisms, both in their dependence upon stress and temperature, and in their effects on fracture behaviour. 

Thus, the stated above results demonstrated, that fractal analysis application for polymers fracture process description allowed to give more general fracture concept, than a dilation one. Let us note, that the dilaton model equations are still applicable in this more general case, at any rate formally. The fractal concept of polymers fracture includes dilaton theory as an individual case for nonfractal (Euclidean) parts of chains between topological fixation points, characterized by the excited states delocalization. The offered concept allows to revise the main factors role in nonoriented polymers fracture process. Local anharmonicity ofintraand intermolecular bonds, local mechanical overloads on bonds and chains molecular mobility are such factors in the first place [9, 10]. 

Watanabe, H., Matsumiya, Y, Osaki, K. Tube dilation process in star-branched cis-polyisoprenes. /. Polym. Sci. (2000) 38, pp. 1024-1036... 

Dynamic properties of interfaces have attracted attention for many years because they help in understanding the behaviour of polymer, surfactant or mixed adsorption layers.6 In particular, interfacial rheology (dilational properties) is crucial for many technological processes (emulsions, flotation, foaming, etc).1 The present work deals with the adsorption of MeC at the air-water interface. Because of its amphiphilic character MeC is able to adsorb at the liquid interface thus lowering the surface tension. Our aim is to quantify how surface active this polymer is, and to determine the rheological properties of the layer. A qualitative and quantitative evaluation of the adsorption process and the dilata-tional surface properties have been realised by dynamic interface tension measurements using a drop tensiometer and an axisymmetric drop shape analysis. 

We have also measured y(t) and e(t) during polymer adsorption for a given concentration. In Figure 6, the e-n curve, the equation state of the layer during the adsorption process, is presented. At low surface pressure, one observes a linear increase of the dilational elastic modulus with the surface pressure n. From the slope of the linear part of the e-n curve, a value of 0.66 was found for the excluded volume critical exponent. The same value has been measured elsewhere with another technique.12 This result indicates that, unlike the excluded volume chain behaviour in the bulk, the air water interface is not a good solvent for MeC. At intermediate surface pressures, the modulus levels off and then increases again until the equilibrium surface pressure is reached. 

The entropy of a network-solvent system will increase because of the tendency of the solvent molecules to disperse in the network. This is in analogy to thermodynamics of the dissolution process of macromolecules in a solvent. In reality, it is necessary to take into consideration the additional effect of interaction between polymer segments and solvent molecules, e.g., by introducing an interaction parameter. The dilation gives rise to an elastic response from the network chains which will oppose the tendency for dilation. 

BOE Bohning, M. and Springer, J., Sorptive dilation and relaxational processes in glassy polymer/gas systems -1. Poly(sulfone) and poly(ether suUbne), Polymer, 39, 5183, 1998. 

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