was found at n+ ¼ 0.63 μmol, where the peaks of both fractions have nearly the same
size. At very high concentrations of cationic charge (Fig. 12b), the particle size
distribution becomes smaller again. It was also confirmed by sedimentation analysis
that the broadness of the so-called flocculation window (range of optimum flocculant
concentration) depends on the hydrophobicity of the flocculant [90].
Nystro ¨m et al. [92, 93] correlated the observed flocculation behavior of calcium
carbonate, induced by mixtures of cationic starch and anionic poly(sodium acrylate)
(NaPA) at various electrolyte concentrations, with the complex properties. A strong
correlation exists between the properties of the PEL mixture, primarily the amount of
complexes formed, and the flocculation behavior. Several mechanisms are involved
in this flocculation process induced by the two polymers. However, interparticle
bridging by the PECs and charge neutralization induced by the deposition of the
complexes were found to be the main reasons for the enhanced flocculation.
As already mentioned, the removal of different dyes is one of the fields where
complexes can successfully be applied [94–97]. The “direct” formation of complexes
between a PC and anionic dyes with two, three, or six sulfonic groups was investigated
using UV–vis spectrophotometry and viscosimetry. Dragan et al. [12] also reported the
formation of complexes having three components. They were formed by the interaction between nonstoichiometric PC/dye complexes with PAs. PCs differed in their
content of the N,N-dimethyl-2-hydroxypropylene ammonium chloride units in the
main chain. NaPA, NaPAMPS, and NaPSS were used as PAs. Crystal Ponceau 6R and
Ponceau 4R with two or three sulfonic groups were used as anionic dyes. The
formation of the three component PC/dye/PA complexes takes place mainly by the
electrostatic interaction between the PA and the free positive charges of the PC/dye
complex. The stoichiometry and the stability of such complexes depends on the PC
structure, the structure and molar mass of PA, the dye structure, and the P:dye molar
ratio. A high amount of the dye was excluded from the complex before the end point,
when a branched PC was used. The higher the solubility of the dye, the lower the
stability of the PC/dye/PA complexes [12].
The mechanism of dye incorporation into triple complexes was also intensively
studied by Zemaitaitiene et al. It was shown that cationic polymer tends to react with
anionic textile finishing chemicals and auxiliaries such as anionic detergents, forming
intermolecular complexes of different stoichiometry. Under controlled conditions,
these complexes can incorporate the dye and precipitate. Surprisingly, the disperse
dye (which was uncharged) also seemed to be bound by polymer–polymer complexes
[98, 99].
Buchhammer et al. [100] investigated the flocculation behavior of two PCs in
comparison with pre-mixed PEC nanoparticles. These results show that depolarization
of the dye solution can be achieved with the PCs as well as with the complex
dispersions, depending on the type and quantity of the flocculant used. However,
significant differences with regard to the removing efficiency and the usable range for
effective flocculation exist. For both PCs used, which differed markedly in terms of
their structure and chain length, a relatively narrow flocculation window was found. It
was also interesting that the concentration ratio c dye /c polymer is determined essentially
from the properties of the PC. The concentration ratio is shifted significantly to lower
52
G. Petzold and S. Schwarz
size. At very high concentrations of cationic charge (Fig. 12b), the particle size
distribution becomes smaller again. It was also confirmed by sedimentation analysis
that the broadness of the so-called flocculation window (range of optimum flocculant
concentration) depends on the hydrophobicity of the flocculant [90].
Nystro ¨m et al. [92, 93] correlated the observed flocculation behavior of calcium
carbonate, induced by mixtures of cationic starch and anionic poly(sodium acrylate)
(NaPA) at various electrolyte concentrations, with the complex properties. A strong
correlation exists between the properties of the PEL mixture, primarily the amount of
complexes formed, and the flocculation behavior. Several mechanisms are involved
in this flocculation process induced by the two polymers. However, interparticle
bridging by the PECs and charge neutralization induced by the deposition of the
complexes were found to be the main reasons for the enhanced flocculation.
As already mentioned, the removal of different dyes is one of the fields where
complexes can successfully be applied [94–97]. The “direct” formation of complexes
between a PC and anionic dyes with two, three, or six sulfonic groups was investigated
using UV–vis spectrophotometry and viscosimetry. Dragan et al. [12] also reported the
formation of complexes having three components. They were formed by the interaction between nonstoichiometric PC/dye complexes with PAs. PCs differed in their
content of the N,N-dimethyl-2-hydroxypropylene ammonium chloride units in the
main chain. NaPA, NaPAMPS, and NaPSS were used as PAs. Crystal Ponceau 6R and
Ponceau 4R with two or three sulfonic groups were used as anionic dyes. The
formation of the three component PC/dye/PA complexes takes place mainly by the
electrostatic interaction between the PA and the free positive charges of the PC/dye
complex. The stoichiometry and the stability of such complexes depends on the PC
structure, the structure and molar mass of PA, the dye structure, and the P:dye molar
ratio. A high amount of the dye was excluded from the complex before the end point,
when a branched PC was used. The higher the solubility of the dye, the lower the
stability of the PC/dye/PA complexes [12].
The mechanism of dye incorporation into triple complexes was also intensively
studied by Zemaitaitiene et al. It was shown that cationic polymer tends to react with
anionic textile finishing chemicals and auxiliaries such as anionic detergents, forming
intermolecular complexes of different stoichiometry. Under controlled conditions,
these complexes can incorporate the dye and precipitate. Surprisingly, the disperse
dye (which was uncharged) also seemed to be bound by polymer–polymer complexes
[98, 99].
Buchhammer et al. [100] investigated the flocculation behavior of two PCs in
comparison with pre-mixed PEC nanoparticles. These results show that depolarization
of the dye solution can be achieved with the PCs as well as with the complex
dispersions, depending on the type and quantity of the flocculant used. However,
significant differences with regard to the removing efficiency and the usable range for
effective flocculation exist. For both PCs used, which differed markedly in terms of
their structure and chain length, a relatively narrow flocculation window was found. It
was also interesting that the concentration ratio c dye /c polymer is determined essentially
from the properties of the PC. The concentration ratio is shifted significantly to lower
52
G. Petzold and S. Schwarz