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The Polysiloxanes$
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James E. Mark, Dale W. Schaefer, and Gui Lin

Print publication date: 2015

Print ISBN-13: 9780195181739

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195181739.001.0001

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Some Characterization Techniques Useful for Polysiloxanes

Some Characterization Techniques Useful for Polysiloxanes

CHAPTER 4 Some Characterization Techniques Useful for Polysiloxanes
The Polysiloxanes

James E. Mark

Dale W. Schaefer

Gui Lin

Oxford University Press

The general approach used in choosing a polymer suitable for a particular application is: . . . Polymerization ↔ Structure ↔ Properties ↔ Application . . . For example, if one wants a polymer for fire-resistant fabrics, then a polymer with good high-temperature properties is required, which implies aromatic structures, which suggest condensation polymerizations. More relevant here, however, would be that a polymer remains elastomeric at low temperatures. This requirement evokes a polymer with high flexibility (low glass transition temperature), which indicates use of the polymerization techniques used with the polysiloxanes. An example of a relevant optical property is the birefringence of a deformed polymer network. This strain-induced birefringence can be used to characterize segmental orientation, and both Gaussian and non-Gaussian elasticity. Infrared dichroism has also been helpful in this regard. In the case of the crystallizable polysiloxane elastomers, orientation is of critical importance with regard to strain-induced crystallization and the tremendous reinforcement it provides. Segmental orientation has also been characterized by fluorescence polarization, deuterium nuclear magnetic resonance (NMR), and polarized infrared spectroscopy. Infrared spectroscopy has been used to characterize the structures of silica-filled polydimethylsiloxane (PDMS). Other optical and spectroscopic techniques are also important, including positron annihilation lifetime spectroscopy, spectroscopic ellipsometry, confocal Raman spectroscopy, and photoluminescence spectroscopy. Surface-enhanced Raman spectroscopy has been made tunable using gold nanorods and strain control on elastomeric PDMS substrates. A great deal of information is now being obtained on filler dispersion and other aspects of elastomer structure and morphology through the use of scanning probe microscopy, which consists of several approaches. One approach is that of scanning tunneling microscopy (STM), in which an extremely sharp metal tip on a cantilever is passed along the surface while measuring the electric current flowing through quantum mechanical tunneling. Monitoring the current then permits maintaining the probe at a fixed height above the surface. Display of probe height as a function of surface coordinates then gives the desired topographic map. One limitation of this approach is the requirement that the sample be electrically conductive. Atomic force microscopy (AFM), on the other hand, does not require a conducting Surface.

Keywords:   Birefringence, Dynamic light scattering (DLS), Ellipsometry, Fluorescence, Infrared spectroscopy (IR), Mesoporous, Neutron scattering, Orientation, Phase separation, Raman spectroscopy

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