Chemistry Reference
In-Depth Information
CHAPTER 7
Elastomeric Networks
7.1 NETWORK FORMATION AND SOME ELASTOMERIC QUANTITIES
7.1.1 Gelation
Gelation is the cross-linking process that leads to the network structures
required for rubberlike elasticity.
1-5
In some cases, gelation can be revers-
ible.
6-8
There have been numerous studies involving theory and simula-
tions exploring gelation and the mechanical properties of the resulting
networks.
9 -20
Cross linking with free radicals is still quite common.
21-27
Radiation has
often been used to carry out the cross linking,
28-36
as have new techniques
known as “click” chemistry.
8,
37-40
Hydrosilylation is also popular.
41-51
Net-
works have even been designed with movable cross links.
52
Finally, reac-
tive groups can be placed at the chain ends or within the chains
themselves.
53-59
Related studies have involved polydimethylsiloxane (PDMS)-based
organogelators,
60
web-to-pillar transitions of gels,
61
and silica aero-
gels.
62
There has also been interest in polysiloxanes in interpenetrat-
ing hydrogels with high oxygen permeabilities
63
and viscoelastic
magnetic gels.
64
Organic-inorganic hybrids with relatively low melting
temperatures also exist,
65
some of which can be made to be
self-healing.
66- 68
Gels are also formed in swelling experiments,
69,
70
which are useful for
equilibrium experiments to characterize network structures.
71
One of the recent topics in this area involves stimuli-responsive gels,
72-75
under the descriptive title of “self-walking gels,”
76
“wormlike motion of
gels,”
77
and “peristaltic motion of gels.”
78
