Polyelectrolyte Multilayers for Fibre Engineering - The Nanoscience and Technology of Renewable Biomaterials - page 132

0.5

0.4

15 k/5 k
70 k/240 k
150 k/750 k

0.3

0.2

0.1

0.0

0 1 2 3 4 5 6

Number of layers

Figure 5.6 Reflectometry data showing the relative change in the reflected signal ( S/S 0 )
whenPEMswereformedfromPAH/PAAofmolecularmass15k/5k,70k/240kand150k/
750kadsorbedatpH7.5/3.5.ThePEMswerestepwiseadsorbedontoSiO 2 byconsecutively
adding thepolyelectrolytesat abackgroundelectrolyteconcentrationof 0.01MNaCl. The
saturation signal for each adsorbed layer was recordedwhen the added polyelctrolyte had
beenadsorbedfor30s.Datafrom(27,35).

layer for the PDADMAC/PSS system. This indicates a change in structure of the PEM
depending on which polymer was adsorbed in the outermost layer; the structure being
more rigid when the anionic polyelectrolyte was outermost than when PDADMAC was
in the external layer.

5.4 Formation of PEM on Fibres

The adsorption of PEMs on wood fibres can be shown using different techniques
as discussed earlier. For PEMs formed from PDADMAC/PSS, PAH/PAA and PAH/
PEDOT:PSS, the adsorption has been studied by destructive elemental analysis of
nitrogen (PDADMAC and PAH) (27, 29, 36) and sulphur (PSS) (29). showing that
there was an increase in the adsorbed amount with increasing number of adsorbed
layers (Figure 5.7). This clearly shows that PEMs are indeed formed on wood fibres
using these polymer systems.
In the case of PAH/PAA, these experiments have shown that there was a higher amount
adsorbed in the first layer, and also that this trend was more significant when PEMs were
formed from low molecular mass polymers. This is most probably due to a somewhat
higher degree of interpenetration of polymers into the external parts of the fibre walls
in the case of low molecular mass polyelectrolytes, as has also been shown by Gimaker
et al . (37), using fluorescently labelled PAH of different molecular weights.
The influence of salt concentration on the formation of PEM on wood fibres was also
investigated with the high molecular mass combination of PDADMAC/PSS. As can be