Some New Characterization Techniques Useful for Polysiloxanes

An example of a relevant optical property is the birefringence of a deformed polymer network.256 This strain-induced birefringence can be used to characterize segmental orientation, and both Gaussian and non-Gaussian elasticity.92,296-302 Infrared dichroism has also been particularly helpful in this regard.82,303 In the case of the crystallizable polysiloxane elastomers, this orientation is of critical importance with regard to strain-induced crystallization, and the tremendous reinforcement it provides.82 

Other optical and spectroscopic techniques are also important, particularly with regard to this segmental orientation. Some examples are fluorescence polarization, deuterium nuclear magnetic resonance (NMR), and polarized infrared spectroscopy.92,256,304 

Atomic force microscopy (ATM), on the other hand, does not require a conducting surface. The probe simply responds to attractions and repulsions from the surface, and its corresponding downward and upward motions are directly recorded to give the relief map of the surface structure. The probe can be either in contact with the surface, or adjacent to it and sensing only coulombic or van der Waals forces. 

An example of an application to polysiloxane elastomers is the characterization of binodal and spinodal phase-separated structures occurring in model PDMS networks.310-312 

Most elastomers require reinforcing fillers to function effectively, and NMR has been used to characterize the structures of such composites as well. One examples is the adsorption of chains onto filler surfaces,334,335 and the strong absorption of these chains into bound rubber, for example PDMS immobilized onto high surface area silica.316,320 Another example is the use of NMR to image the filler or polymer itself.336-342 

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