values with the long chain PMADAMBQ that is sterically stabilized. For application,
this means that long chains as well as branched polymers are particularly effective
when used as flocculants for depolarization of textile effluents containing, e.g.,
disperse dyes at low concentration. Further, it was shown that the dye structure had a
marked influence. The dye content after separation was at least 15% for the disperse
dye Celliton Fast Blue, whereas the degree of dye removal was much better for Cibacet
Red [104]. Solid–liquid separation processes in general use highly hydrophilic linear
polyelectrolytes with excellent water solubility as processing aids, but not all flocculation processes can be carried out with sufficient efficiency. These disadvantages may
be overcome using associating or aggregating cationic polyelectrolytes as flocculants.
A significant enhancement of the flocculation properties can be achieved by introduction of hydrophobic functionalities into the PEL backbone [101–103].
4.4 Polymer–Surfactant Complexes
It was also interesting to investigate the application of pre-mixed polymer–surfactant
complexes (PSCs). Such mixtures of polymers and surfactants are common in many
industrial formulations. The interaction between surfactants and water-soluble
polymers provides special effects, e.g. enhancing the surface activity, stabilizing
foams and emulsions, etc. It is, therefore, very important to study the interaction
between surfactants and water-soluble polymers, especially between components of
opposite charge. The first results were described in the literature of the 1970s, and
from 1980 until now much work has been done to improve the understanding of such
systems [104–107]. Very detailed investigations using different characterization
methods such as surface tensiometry, light scattering, neutron scattering, NMR or
ESR, and surface rheological methods [108–123] are mentioned. Usually, mixed
solutions at fixed PEL and variable surfactant concentrations are investigated and it
can be shown that the association between PEL and oppositely charged surfactant
starts at very low surfactant concentration (typically one to three orders of magnitude
below the cmc of the surfactant). The degree of surface tension lowering depends not
only on the type of PEL (on their hydrophobicity, charge density, molar mass), but
also on the mixing conditions (order of addition, influence of time) and salt content
[124]. In most studies, a fixed polyelectrolyte amount was added to solutions of an
oppositely charged surfactant (the “polymer to surfactant regime” [123]). Because
the interaction between polymer and surfactant starts at very low surfactant concentration, basic research is often carried out below the cmc, but for industrial
applications the interaction with polymers at higher surfactant concentration
is also important. However, despite the importance and common use of PSCs there
are only very few publications about application-relevant properties. As mentioned
above, it is possible to tailor stable, differently charged dispersions made from
oppositely charged polyelectrolytes and surfactants that can be used for different
applications, such as surface modification of powders, sorption of organic molecules
from wastewater, or as flocculants. As an example, complexes with PDADMAC as
PC and sodium dodecylsulfate (SDS) as an anionic surfactant are shown in Fig. 13.
Polyelectrolyte Complexes in Flocculation Applications
53
this means that long chains as well as branched polymers are particularly effective
when used as flocculants for depolarization of textile effluents containing, e.g.,
disperse dyes at low concentration. Further, it was shown that the dye structure had a
marked influence. The dye content after separation was at least 15% for the disperse
dye Celliton Fast Blue, whereas the degree of dye removal was much better for Cibacet
Red [104]. Solid–liquid separation processes in general use highly hydrophilic linear
polyelectrolytes with excellent water solubility as processing aids, but not all flocculation processes can be carried out with sufficient efficiency. These disadvantages may
be overcome using associating or aggregating cationic polyelectrolytes as flocculants.
A significant enhancement of the flocculation properties can be achieved by introduction of hydrophobic functionalities into the PEL backbone [101–103].
4.4 Polymer–Surfactant Complexes
It was also interesting to investigate the application of pre-mixed polymer–surfactant
complexes (PSCs). Such mixtures of polymers and surfactants are common in many
industrial formulations. The interaction between surfactants and water-soluble
polymers provides special effects, e.g. enhancing the surface activity, stabilizing
foams and emulsions, etc. It is, therefore, very important to study the interaction
between surfactants and water-soluble polymers, especially between components of
opposite charge. The first results were described in the literature of the 1970s, and
from 1980 until now much work has been done to improve the understanding of such
systems [104–107]. Very detailed investigations using different characterization
methods such as surface tensiometry, light scattering, neutron scattering, NMR or
ESR, and surface rheological methods [108–123] are mentioned. Usually, mixed
solutions at fixed PEL and variable surfactant concentrations are investigated and it
can be shown that the association between PEL and oppositely charged surfactant
starts at very low surfactant concentration (typically one to three orders of magnitude
below the cmc of the surfactant). The degree of surface tension lowering depends not
only on the type of PEL (on their hydrophobicity, charge density, molar mass), but
also on the mixing conditions (order of addition, influence of time) and salt content
[124]. In most studies, a fixed polyelectrolyte amount was added to solutions of an
oppositely charged surfactant (the “polymer to surfactant regime” [123]). Because
the interaction between polymer and surfactant starts at very low surfactant concentration, basic research is often carried out below the cmc, but for industrial
applications the interaction with polymers at higher surfactant concentration
is also important. However, despite the importance and common use of PSCs there
are only very few publications about application-relevant properties. As mentioned
above, it is possible to tailor stable, differently charged dispersions made from
oppositely charged polyelectrolytes and surfactants that can be used for different
applications, such as surface modification of powders, sorption of organic molecules
from wastewater, or as flocculants. As an example, complexes with PDADMAC as
PC and sodium dodecylsulfate (SDS) as an anionic surfactant are shown in Fig. 13.
Polyelectrolyte Complexes in Flocculation Applications
53