treatment resulted in by far the highest joint strength for a given degree of contact or
for a given number of nodes (Fig. 18). Cohesive failure of the paper sheets was seen to
some extent (fibre fragments were pulled out), showing the great adhesive strength of
the surface treatment. With increasing surface charge of the fibres and with PAE
added, the tensile index of the paper increased significantly. With PDADMAC
addition, however, the tensile index decreased. This was ascribed to a lower
conformability of the fibres with adsorbed PDADMAC than with PAE.
The conclusion that a large number of just sufficiently compliant contact points
between the fibres would be the most advantageous suggests that surface treatment
with a PEC should offer great possibilities. Although only a few studies have been
performed on this specific topic, current research suggests the potential of PECs to
increase both the number of contact points between two surfaces and, of course, to
offer a way to steer the mechanical properties of the joint by appropriate choice of
polymer components and/or preparation conditions.
5 Future Outlook
The advantages of PECs lie in their three-dimensional structure and the relatively low
polyelectrolyte concentration needed to reach this structure as compared with, for
example, polymer lattices. Another major advantage is the possibility to vary the
structure and properties of the complexes simply by changing their composition. This
is more important than ever considering the large efforts that are needed to acquire
necessary permits for the introduction of new chemicals, since the PECs can be
prepared by already accepted polymers/polyelectrolytes and/or nanoparticles. The
structural integrity of the PECs also allows them to retain a three-dimensional
structure when adsorbed at a solid–liquid interface, which is essential, e.g., for
flocculation efficiency. Flocculation is interesting in many industrial applications,
not only for the paper industry but also in, e.g., waste water treatment.
Despite the rich literature on PECs, only a limited number of polymers (and
nanoparticles) have been used to prepare PECs so far. Therefore, it would be
interesting to test a more extensive range of other types of polymers, including
block-copolymers, since the properties of the polymers and thereby the PECs can
be tailored to reach a wider property space of the PECs. An additional possibility with
block-copolymers would be to investigate other complexing interactions when
forming PECs, apart from the pure electrostatic interactions that are the most commonly used today. Another interesting development is the combination of
nanoparticles and polyelectrolytes for adhesive surface engineering. Recent results
show that both adhesive pull-off forces and the work of adhesion can be tailored with
this concept [67]. It has recently also been identified [68] that in order to form strong
interfacial joints it is necessary to have a a) high interfacial adhesion b) a large
molecular contact area and c) a low compliance of the material in the contact zone. By
selecting the right starting materials for the PECs and by selecting the right preparation and adsorption conditions for the complexes these materials could be ideal for
tailoring adhesion.
20
C. Ankerfors and L. Wa ˚gberg
for a given number of nodes (Fig. 18). Cohesive failure of the paper sheets was seen to
some extent (fibre fragments were pulled out), showing the great adhesive strength of
the surface treatment. With increasing surface charge of the fibres and with PAE
added, the tensile index of the paper increased significantly. With PDADMAC
addition, however, the tensile index decreased. This was ascribed to a lower
conformability of the fibres with adsorbed PDADMAC than with PAE.
The conclusion that a large number of just sufficiently compliant contact points
between the fibres would be the most advantageous suggests that surface treatment
with a PEC should offer great possibilities. Although only a few studies have been
performed on this specific topic, current research suggests the potential of PECs to
increase both the number of contact points between two surfaces and, of course, to
offer a way to steer the mechanical properties of the joint by appropriate choice of
polymer components and/or preparation conditions.
5 Future Outlook
The advantages of PECs lie in their three-dimensional structure and the relatively low
polyelectrolyte concentration needed to reach this structure as compared with, for
example, polymer lattices. Another major advantage is the possibility to vary the
structure and properties of the complexes simply by changing their composition. This
is more important than ever considering the large efforts that are needed to acquire
necessary permits for the introduction of new chemicals, since the PECs can be
prepared by already accepted polymers/polyelectrolytes and/or nanoparticles. The
structural integrity of the PECs also allows them to retain a three-dimensional
structure when adsorbed at a solid–liquid interface, which is essential, e.g., for
flocculation efficiency. Flocculation is interesting in many industrial applications,
not only for the paper industry but also in, e.g., waste water treatment.
Despite the rich literature on PECs, only a limited number of polymers (and
nanoparticles) have been used to prepare PECs so far. Therefore, it would be
interesting to test a more extensive range of other types of polymers, including
block-copolymers, since the properties of the polymers and thereby the PECs can
be tailored to reach a wider property space of the PECs. An additional possibility with
block-copolymers would be to investigate other complexing interactions when
forming PECs, apart from the pure electrostatic interactions that are the most commonly used today. Another interesting development is the combination of
nanoparticles and polyelectrolytes for adhesive surface engineering. Recent results
show that both adhesive pull-off forces and the work of adhesion can be tailored with
this concept [67]. It has recently also been identified [68] that in order to form strong
interfacial joints it is necessary to have a a) high interfacial adhesion b) a large
molecular contact area and c) a low compliance of the material in the contact zone. By
selecting the right starting materials for the PECs and by selecting the right preparation and adsorption conditions for the complexes these materials could be ideal for
tailoring adhesion.
20
C. Ankerfors and L. Wa ˚gberg