Chemistry Reference
In-Depth Information
CHAPTER 6
Surfaces
6.1 INTRODUCTION
Because of the great importance of the surface properties of the polysilox-
anes, this topic is treated separately in this chapter.
6.2 INTERACTIONS WITH WATER
6.2.1 Hydrophilicity and Hydrophobicity
Hydrophobic polysiloxanes having simple aliphatic or aromatic side
groups have surfaces that show essentially no attraction to water. In fact,
polysiloxanes can serve as water repellants. This property is very useful
for applications such as protective coatings on historical monuments
1
and
for controlling the surfaces of other polymers,
2
sensors,
3
and quantum
dots.
4
Hydrophobic surfaces can be readily regenerated if the surface be-
comes damaged. Regeneration occurs by rearrangements of the polysilox-
ane chains so that the hydrophobic methyl groups are once again covering
the surface. The flexibility of the siloxane chain backbone facilitates this
process.
5
It is also possible to prepare hydrophobic films using methyl-
modified siloxane melting gels.
6
Glass surfaces
7
or wool fibers8
8
can be
coated with polydimethylsiloxane (PDMS) to make them more
hydrophobic.
In some cases, it is necessary to modify a polysiloxane surface to make
it hydrophilic or hydrophobic. Hydrophobization is one aspect of the gen-
eral topic of modifying and managing the properties of polymer sur-
faces.
9-12
An important example involves soft contact lenses that contain
