Chemistry Reference
In-Depth Information
Figure 6.1:
Sketch showing the usual definition of the contact angle, for a very hydrophobic surface
(high contact angle, left) and very hydrophilic (low contact angle right).
with water.
20,
21,
47,
48
Both static and dynamic techniques have been
used.
47
The left portion of figure 6.1 shows a hydrophobic surface (with a
large contact angle between the water droplet and the surface), and the
right portion shows a hydrophilic one with a small contact angle. A
major problem is contamination of the water droplet from the polymer
surface, making reproducibility very difficult.47
47
Unusual increases in
adhesion hysteresis and frictional forces have been observed when
PDMS lenses were slid on smooth glassy surfaces after a period of
aging.
49
Applications in the biological area include stabilization of water in
silicone oil emulsions by peptide-silicone hybrid polymers
50
and the
mitigation of reactive human cell adhesion on PDMS by immobilized
trypsin.
51
6.3.2 Wettability
A polymer should be readily wet with water for applications such as con-
tact lenses and for the preparation of hydrogels for a variety of biomedical
applications. Increased wettability
52-55
is reflected by reduced values of
the contact angle of the polymer with water. Another application is sili-
cone surface modification of wool for self-cleaning.
56
6.3.3 Spreading
In addition to the equilibrium properties there are important dynamic
properties of surfaces. One example is the rate of spreading of PDMS on
