4 Pre-mixed PECs as Flocculants
4.1 Complex Formation and Characterization
It is well known that oppositely charged PEL will form complexes over a broad
range of stoichiometric ratios.
Such interactions were investigated, among others, by Tsuchida [70], Dubin [71],
Philipp and Dautzenberg [72, 73], Mu ¨ller [74–76], Pergushov and Mu ¨ller [77],
Dragan [12], and the group of Kabanov [78, 79]. Some of the most important PEL
used for complex formation are summarized in Table 2 and in works by Dragan [12]
and Jaeger et al. [80].
Kabanov et al. described the formation of water-soluble nonstoichiometric PECs
(NPEC) as a result of the interaction of oppositely charged PEL in nonequivalent
ratios. They are obtained by the interaction of polyions with different degree of
polymerization, i.e., different molar masses. The polyions are introduced into the
reaction in nonequivalent ratios so that a relatively long-chained host PEL (HPE) is
incorporated into an NPEC particle in some excess in comparison with the opposite
charged relatively short-chained guest PEL (GPE). Such NPEC are water-soluble
because of their big differences in molar mass, and their properties can be studied by
classical methods. An NPEC can be represented as a peculiar block copolymer with
alternating hydrophobic double-strand blocks and hydrophilic single-strand blocks
composed of sequences of HPE units incorporated in NPEC in excess (Fig. 10). One
of the most important properties of NPEC is their ability to participate in intermacromolecular exchange and substitution reactions in aqueous solutions, as described by
Kabanov [77]. These properties can be used to flocculate and separate materials
such as dyes.
PEC nanoparticles, prepared by mixing solutions of the commercial low-cost PEL
components PEI and PAC, were described by Mu ¨ller et al. [75]. It was found that the
size and internal structure of PEI/PAC particles can be regulated by process, media,
and structural parameters. The mixing order, mixing ratio, PEL concentration, pH, and
molar mass were found to be especially sensitive parameters for regulating the size
(diameter) of spherical PEI/PAC nanoparticles, in the range between 80 and 1,000 nm,
in a defined way.
The formation of PECs using structurally uniform and strongly charged cationic
and anionic modified alternating maleic anhydride copolymers was described by
Mende [81]. The hydrophobicity of the PEL was changed by the comonomers
(ethylene, isobutylene, and styrene). Additionally, the nÀ/n+ ratio of the molar
charges of the PEL and the procedure of formation were varied. Dynamic light
scattering indicates that, besides large PEC particle aggregates, distinct smaller and
more compact particles were formed by the copolymers having the highest
hydrophobicity (styrene). These findings could be proved by AFM. Measurements
of fractal dimension, root mean square roughness, and the surface profiles of the
PEC particles adsorbed on mica allow the following conclusions: the higher the
hydrophobicity of the polyelectrolytes, the broader the particle size distribution and
Polyelectrolyte Complexes in Flocculation Applications
45
4.1 Complex Formation and Characterization
It is well known that oppositely charged PEL will form complexes over a broad
range of stoichiometric ratios.
Such interactions were investigated, among others, by Tsuchida [70], Dubin [71],
Philipp and Dautzenberg [72, 73], Mu ¨ller [74–76], Pergushov and Mu ¨ller [77],
Dragan [12], and the group of Kabanov [78, 79]. Some of the most important PEL
used for complex formation are summarized in Table 2 and in works by Dragan [12]
and Jaeger et al. [80].
Kabanov et al. described the formation of water-soluble nonstoichiometric PECs
(NPEC) as a result of the interaction of oppositely charged PEL in nonequivalent
ratios. They are obtained by the interaction of polyions with different degree of
polymerization, i.e., different molar masses. The polyions are introduced into the
reaction in nonequivalent ratios so that a relatively long-chained host PEL (HPE) is
incorporated into an NPEC particle in some excess in comparison with the opposite
charged relatively short-chained guest PEL (GPE). Such NPEC are water-soluble
because of their big differences in molar mass, and their properties can be studied by
classical methods. An NPEC can be represented as a peculiar block copolymer with
alternating hydrophobic double-strand blocks and hydrophilic single-strand blocks
composed of sequences of HPE units incorporated in NPEC in excess (Fig. 10). One
of the most important properties of NPEC is their ability to participate in intermacromolecular exchange and substitution reactions in aqueous solutions, as described by
Kabanov [77]. These properties can be used to flocculate and separate materials
such as dyes.
PEC nanoparticles, prepared by mixing solutions of the commercial low-cost PEL
components PEI and PAC, were described by Mu ¨ller et al. [75]. It was found that the
size and internal structure of PEI/PAC particles can be regulated by process, media,
and structural parameters. The mixing order, mixing ratio, PEL concentration, pH, and
molar mass were found to be especially sensitive parameters for regulating the size
(diameter) of spherical PEI/PAC nanoparticles, in the range between 80 and 1,000 nm,
in a defined way.
The formation of PECs using structurally uniform and strongly charged cationic
and anionic modified alternating maleic anhydride copolymers was described by
Mende [81]. The hydrophobicity of the PEL was changed by the comonomers
(ethylene, isobutylene, and styrene). Additionally, the nÀ/n+ ratio of the molar
charges of the PEL and the procedure of formation were varied. Dynamic light
scattering indicates that, besides large PEC particle aggregates, distinct smaller and
more compact particles were formed by the copolymers having the highest
hydrophobicity (styrene). These findings could be proved by AFM. Measurements
of fractal dimension, root mean square roughness, and the surface profiles of the
PEC particles adsorbed on mica allow the following conclusions: the higher the
hydrophobicity of the polyelectrolytes, the broader the particle size distribution and
Polyelectrolyte Complexes in Flocculation Applications
45