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4.7 BRILLOUIN SCATTERING
The application of Brillouin scattering to the characterization of PDMS
networks was found to be particularly useful for looking at glassy-state
properties of such elastomers at very high frequencies. 114 -116
4.8 PULSE PROPAGATION
Another example of a relatively new technique for the noninvasive, non-
destructive characterization of network structures involves ultrasound
pulse-propagation measurements. 117, 118 The goal here is the rapid determi-
nation of the spacing between junctions and between entanglements in a
network structure. The delay in a pulse passing through the network is
used to obtain such information on the network structure. 114 Ultrasonic
methods have also been used to study interdiffusion between two samples
of PDMS differing only in molecular weight. 119
This list is essentially an extension of parts of chapter 2, and many of
the techniques described here are also useful for characterizing the com-
posites described in chapter 9.
4.9 THEORY AND SIMULATIONS
Some of the earliest studies involved determination of the potential func-
tion governing low-frequency bending modes of disiloxane, 120 the impor-
tance of (p-d)π bonding, 121 characterization of helical polysiloxane
chains, 122 the molecular states of silicon-containing compounds in gen-
eral, 123 ab initio structure calculations 124 and molecular modeling of elas-
tic behavior. 125 More recent examples include molecular dynamics and
integral equations, 126 force fields,127, 127, 128 and finite element simulations of
mechanical property evolution during vulcanization. 129 Artificial intelli-
gence approaches have been used in the polysiloxane area, including stud-
ies of synthesis, solution properties, metal ion sorption, liquid-crystalline
behavior, and fluorescence of composites containing complexed rare
earths. 130
Simulations and theoretical calculations have also been carried out for
PDMS networks 131-133 and single chains 134, 135 under deformation. Finally,
investigations have clarified important aspects of polysiloxane permea-
bilities, 136, 137 interfacial structure, 138 and elasticity using an expansion
approach. 139
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