Biomedical Engineering Reference
In-Depth Information
Figure5.19
Schematicrepresentationof theprobablemixingofpolyelectrolytesacross the
interfaceof twoPEMsonadjacentsurfaces.It issuggestedthatthisintermixingisvitalforthe
formationofstrongadhesivejointsbetweenthesurfacesandthatthemolecularmobilityand
thenumberofinteractingchainendsareimportantforthedevelopmentofstrongadhesionat
shortcontacttimes.
between the substrates in water can be described by the following equation (54):
2
γ
lv
cos
θ
where
W
sl
is the adhesion between two surfaces in water,
W
sl
is the adhesion between
two surfaces in vacuum, and
γ
lv
is the surface tension. This means that the adhesion
between two hydrophobic surfaces (i.e. with a contact angle
>
90
◦
) in water will be
greater than that between two surfaces that are more hydrophilic.
Fibres in water are forced towards each other more strongly when the contact angle is
increased. A larger contact angle results in a better contact between the fibres, which is
important for the formation of strong, dry fibre-fibre joints. Considering the hypothesis
that the level of wettability is an important factor for creating strong adhesion between
the fibre, these results are in agreement with the results of individual fibre measurements
showing that fibres treated at pH 7.5/3.5 have a lower wettability than fibres treated
at pH 7.5/7.5. This hypothesis is also consistent with the results for high molecular
PDADMAC/PSS which showed a higher paper strength and a lower wettability when
PDADMAC was in the outermost layer.
W
sl
=
W
sv
−
5.7
Concluding Remarks
This chapter has focused on the formation of PEM on model surfaces and on fibres,
in order to describe how these layers can be used to improve the interaction between
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