The shape of the water drops on the PE film is determined by a few layers of atoms at the surface. It is a region which is about 1 nm thick. Altering the chemistry in such a shallow layer can considerably improve the material's properties.
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Polyethylene film with water drops in three different zones |
The activation of a surface means that it is oxidized in order to form functional
groups which can interact with other substance, be it water, a paint or an adhesive.
For many applications (e.g. printing on plastic bags, gluing polyolefins), the exact
type of functional groups is not important. The use of highly energetic means as
electrical discharges for surface activation results in a complex mixture of
functional groups which can only be tuned in a rather narrow range. If a defined
function is needed, we use the functional groups formed in a very efficient
activation process (-OH, C=O, COOH and others ) as anchor groups for more specific
reactions. We have developed a reaction toolbox for preparing various functional
groups starting from different anchors. Some examples are shown in the picture.
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Polypropylene surface which was prepared by the following steps: oxidation / activation, spacer coupling, streptavidine coupling, immobilization of a biotinylated antibody. |
The anchor groups (blue) couple molecules that can act as spacers (green) where R
defines the length and the properties. At the other end of the spacer, there is a
functional group for coupling for example an antibody. The picture provides an
imagination about the sizes and concentrations.
The spacer can have additional function like for example preventing dispersive
interaction with coupled proteins which would cause a denaturation.