Chemistry Reference
In-Depth Information
6.5 RADIATION TREATMENTS
6.5.1 Plasmas and Photons
Modification of surfaces by radiation treatment can be difficult to control
because of the high energies involved. The most extensively used treat-
ment of this type involves modifications by chemical transformation of
surface groups or adsorbed molecules, or induced polymerization of suita-
ble monomers.
Transformation of PDMS can yield less hydrophobic surfaces, using
radio-frequency plasmas,
84
argon or hydrogen plasmas,
85
oxygen plas-
mas,
86, 87
helium plasmas,
88
water plasmas,
89
or other environments.
90
he
same treatments can be applied to molecules coated onto PDMS (e.g., im-
idazole and some of its derivatives) to facilitate attaching antimicrobial
drugs onto the PDMS surface.
91
Other examples are layer-by-layer modifi-
cations using acrylamides, sulfonates, and trimethylammonium chloride
salts.
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A final example uses maleic anhydride to promote the formation of
dicarboxylic acid groups on PDMS surfaces.
93
Plasma polymerization has
also been used to modify fillers and curatives used in a variety of
elastomers.
94
An example of plasma polymerization is acrylic acid coating of PDMS.
The polymerized coatings yielded hydrophilic or patterned hydrophilic/
hydrophobic surfaces that were quite stable.
95
These materials were useful
in PDMS microchannels in lab-on-a-chip devices or in soft microlithogra-
phy. Maleic anhydride has also been used in these polymerizations.
89
Pho-
tons have also been used to modify surfaces.
96
6.5.2 UV and UV/Ozone Treatments
UV (ultraviolet) irradiation of PDMS surfaces has been described and
compared to the results from water-plasma treatments and plasma po-
lymerization.
89
These treatments affect cracking of thin coatings of PDMS
during stretching.
The use of UV in the presence of ozone is illustrated by the conversion
of portions of PDMS surfaces to more hydrophilic SiO
x
.
97,
98
U V/oz one
treatments were also used to make poly(vinylmethylsiloxane) surfaces
more hydrophilic, but only about one-twentieth the PDMS exposure time
was required.
99
Such treatments have also improved the permeability of
PDMS membranes.
100
