Birefringence elastomeric networks

The Theory of Kuhn and Grun. The theory of birefringence of deformed elastomeric networks was developed by Kuhn and Griin and by Treloar on the basis of the same procedure as that used for the development of the classical theories of rubber-like elasticity (48,49). The pioneering theory of Kuhn and Griin is based on the affine network model that is, upon the application of a macroscopic deformation the components of the end-to-end vector for each network chain are assumed to change in the same ratio as that of the corresponding dimensions of the macroscopic sample. 

Recently, new models were proposed which can indeed be used to characterize the structure of real elastomeric networks in view of their mechanical properties 6, 7 However several parameters are necessary to describe the relationship between molecular and macroscopic deformations and therefore stress-strain measurements are generally not sufficient to conclude without any ambiguity on the validity of these elaborated theories- Another possible test consists in measuring molecular orientation in stretched rubbery networks- With this in view, the photoelastic properties of rubbers have been widely investigated However birefringence data... 

Viers, B. D. Mark, J. E., Elastomeric Properties of Polysiloxane Networks Birefringence Measurements on Bimodal Elastomers That Are Presumed to Be Spatially Inhomogeneous J. Inorg. Organomet. Polym. Mater. 2007,17,... 

BirGfring6nC6 of Polymer Networks. Elastomeric polymer networks deserve special mention because their cross-linked structure gives them unique physical properties, unlike those of other polymers. Covalently bonded networks are insoluble in any solvent, even in those that dissolve their precursor polymers. Optical techniques such as strain-induced birefringence allow the development of structure-property relationships as well as the study of their optical properties. Here we review some of the classical theories as well as some of the latest developments in the field. 

Birefringence of Phantom Networks. This theory is the basis for all theories that deal with birefringence of elastomeric polymer networks. It is based on the phantom network model of rubber-like elasticity. This model considers the network to consist of phantom (ie, non-interacting) chains. Consider the instantaneous end-to-end distance r for the ith network chain at equilibrium and at fixed strain. For a perfect (ie, no-defects) phantom network the birefringence induced... 

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