mixture: first, Z ¼ [GPE]/[HPE] (here, the basemolar concentrations of the polymeric components in a reaction mixture are given in the brackets) and second, the
stoichiometry of the formed IPEC, ’ ¼ N GPE /N HPE (here, the amounts of monomer
units of the polymeric components incorporated into an IPEC are given). These
parameters are defined already in early works [31, 32] and will be used throughout
this review.
Figure 3 illustrates transformations of the water-soluble nonstoichiometric
IPECs upon increasing Z. Here, three regions (A, B, and C) are marked on the
Z-axis, where Z cr and Z lim correspond to the boundaries between the regions A and
B and B and C, respectively, with the stoichiometry of the IPEC changing differently in each region. This scheme describes the behavior of mixtures of oppositely
charged polyelectrolytes with considerably different degrees of polymerization,
where DP HPE ) DP GPE (here, DP is the degree of polymerization of the
corresponding polyion) in the range 0 < Z 1.
In region A, 0 < Z Z cr and free (uncomplexed) macromolecules of HPE and
IPEC species with stoichiometry being constant and equal to ’ cr ¼ DP GPE /DP HPE
coexist in the solution. Numerous experimental results provide evidence that each
of the IPEC species contains only one HPE chain. Disproportionation observed in
region A results from an insufficient amount of GPE chains, which cannot occupy
all HPE chains in the mixture. With increasing Z, the fraction of free HPE chains in
the reaction mixture linearly decreases, with all HPE chains being incorporated into
IPEC species at Z ¼ Z cr .
In region B, Z cr < Z Z lim and all HPE chains are occupied but they are able
to host further GPE. Experimental results indicate that GPE chains, which are
additionally incorporated into the IPEC species of stoichiometry ’ cr , are uniformly
distributed among the macromolecular co-assemblies. However, a change of
charge-to-charge stoichiometry of the IPEC species upon increasing Z in the region
B has not been investigated in detail so far. It was only found that IPEC species with
’ > ’ lim lose their solubility in aqueous media. This happens at Z ¼ Z lim ¼ ’ lim .
On further addition of GPE to a mixture of oppositely charged polymeric components
(Z lim < Z 1), the system becomes heterogeneous (the region C). As previously
described [26, 33], IPEC species considerably differing in their charge-to-charge
stoichiometries coexist in the mixture of oppositely charged polyelectrolytes.
Particles of an insoluble IPEC in region C are present in a colloidally dispersed
state and can be easily separated from the reaction mixture, for example, by
centrifugation. A direct determination of their charge-to-charge stoichiometry by
means of elemental analysis indicates that it remains constant and corresponds to
the equimolar ratio between charged groups of HPE and GPE (i.e., ’ ¼ 1). At the
same time, a water-soluble nonstoichiometric IPEC with stoichiometry ’ ¼ ’ lim
remains in the solution. At Z ¼ 1, only a precipitate of a stoichiometric IPEC
(’ ¼ 1) is formed and the supernatant contains no polyions.
These insoluble stoichiometric IPECs have found their application as binders of
various disperse systems, including soils and grounds, thus acting as effective agents
for preventing wind and/or water erosion. Specifically, they have been used to
suppress spreading of radioactive contamination in soils and grounds resulting from
accidents in atomic power stations [10, 14–16].
180
D.V. Pergushov et al.
stoichiometry of the formed IPEC, ’ ¼ N GPE /N HPE (here, the amounts of monomer
units of the polymeric components incorporated into an IPEC are given). These
parameters are defined already in early works [31, 32] and will be used throughout
this review.
Figure 3 illustrates transformations of the water-soluble nonstoichiometric
IPECs upon increasing Z. Here, three regions (A, B, and C) are marked on the
Z-axis, where Z cr and Z lim correspond to the boundaries between the regions A and
B and B and C, respectively, with the stoichiometry of the IPEC changing differently in each region. This scheme describes the behavior of mixtures of oppositely
charged polyelectrolytes with considerably different degrees of polymerization,
where DP HPE ) DP GPE (here, DP is the degree of polymerization of the
corresponding polyion) in the range 0 < Z 1.
In region A, 0 < Z Z cr and free (uncomplexed) macromolecules of HPE and
IPEC species with stoichiometry being constant and equal to ’ cr ¼ DP GPE /DP HPE
coexist in the solution. Numerous experimental results provide evidence that each
of the IPEC species contains only one HPE chain. Disproportionation observed in
region A results from an insufficient amount of GPE chains, which cannot occupy
all HPE chains in the mixture. With increasing Z, the fraction of free HPE chains in
the reaction mixture linearly decreases, with all HPE chains being incorporated into
IPEC species at Z ¼ Z cr .
In region B, Z cr < Z Z lim and all HPE chains are occupied but they are able
to host further GPE. Experimental results indicate that GPE chains, which are
additionally incorporated into the IPEC species of stoichiometry ’ cr , are uniformly
distributed among the macromolecular co-assemblies. However, a change of
charge-to-charge stoichiometry of the IPEC species upon increasing Z in the region
B has not been investigated in detail so far. It was only found that IPEC species with
’ > ’ lim lose their solubility in aqueous media. This happens at Z ¼ Z lim ¼ ’ lim .
On further addition of GPE to a mixture of oppositely charged polymeric components
(Z lim < Z 1), the system becomes heterogeneous (the region C). As previously
described [26, 33], IPEC species considerably differing in their charge-to-charge
stoichiometries coexist in the mixture of oppositely charged polyelectrolytes.
Particles of an insoluble IPEC in region C are present in a colloidally dispersed
state and can be easily separated from the reaction mixture, for example, by
centrifugation. A direct determination of their charge-to-charge stoichiometry by
means of elemental analysis indicates that it remains constant and corresponds to
the equimolar ratio between charged groups of HPE and GPE (i.e., ’ ¼ 1). At the
same time, a water-soluble nonstoichiometric IPEC with stoichiometry ’ ¼ ’ lim
remains in the solution. At Z ¼ 1, only a precipitate of a stoichiometric IPEC
(’ ¼ 1) is formed and the supernatant contains no polyions.
These insoluble stoichiometric IPECs have found their application as binders of
various disperse systems, including soils and grounds, thus acting as effective agents
for preventing wind and/or water erosion. Specifically, they have been used to
suppress spreading of radioactive contamination in soils and grounds resulting from
accidents in atomic power stations [10, 14–16].
180
D.V. Pergushov et al.