They resemble star-shaped polyelectrolytes with a large number of arms, though
the number of arms in such macromolecular self-assemblies might change if the
micelles are of “dynamic” nature, that is, if they are able to change their aggregation
numbers with variations in the environmental conditions. Historically, the micelles
of ionic amphiphilic diblock copolymers were the first star-like polyionic species
involved in interpolyelectrolyte complexation and their IPECs have attracted
considerable attention during the recent years.
Because the micelles generated by ionic amphiphilic diblock copolymers in
aqueous media possess polyelectrolyte coronas, they are naturally expected to
form IPECs with oppositely charged polyions. To the best of our knowledge, the
first attempt to study interpolyelectrolyte complexation in such systems was
performed by Talingting et al. [59], who reported a study on the interaction of
protonated polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VPH
þ ) micelles with
linear PSSNa of different molecular weights. Under a considerable excess of
PSSNa to avoid any bridging or aggregation by linear polyions, the formation
of macromolecular co-assemblies with a large mass excess (by a factor of ca.
5–6) of the charged groups of the PSSNa over charged groups of P2VPH
þ was
found, thereby leading to charge inversion of the PS-b-P2VPH
þ micelles. This
concomitant massive charge overcompensation resulting from the considerable
molar excess (ca. 4.7–5.5) of sulfonate groups over pyridinium ones causes the
formed IPECs to be colloidally stable.
Water-soluble (or colloidally stable) IPECs formed by oppositely charged
micelles with polyelectrolyte coronas and linear polyions were subsequently
found for a number of other systems. In particular, a detailed characterization of
such macromolecular co-assemblies was performed for polyisobutylene-block-poly
(sodium methacrylate) (PIB-b-PMANa) micelles complexed with a linear P4VPQ
[60–62]. It was found that the formed IPECs remain water-soluble only when
loading of the original micelles (acting as a HPE) by the linear polyion (acting as
a GPE) does not exceed a certain threshold value. Such nonstoichiometric IPECs
were thoroughly examined by means of various techniques, which provided evidence on their peculiar core–shell–corona (also referred to as “onion-like”) structure (Fig. 10a). Specifically, each of the complex species comprises a hydrophobic
core from nonpolar blocks, which is surrounded by a layer (inner shell) assembled
from oppositely charged segments of the polymeric counterparts, and a hydrophilic
corona (outer shell) from excess segments of ionic blocks, which do not form
interpolymer salt bonds.
A similar multilayer structure with an inner complex shell was also proposed
for IPECs formed by PS-b-P4VPQ, PS-b-PANa, and PS-b-PMANa micelles
complexed with oppositely charged linear polyions [63–65]. In these cases, a
polyelectrolyte corona is formed either by excess segments of ionic blocks of
the copolymer (no overcharging of the original micelles by the linear polymeric
counterpart) or by excess segments of the linear polyion (overcharging of the
original micelles by the linear polymeric counterpart), depending on the actual
ratio between molar concentrations of charged groups of the polymeric components
in the system.
Advanced Functional Structures Based on Interpolyelectrolyte Complexes
193
the number of arms in such macromolecular self-assemblies might change if the
micelles are of “dynamic” nature, that is, if they are able to change their aggregation
numbers with variations in the environmental conditions. Historically, the micelles
of ionic amphiphilic diblock copolymers were the first star-like polyionic species
involved in interpolyelectrolyte complexation and their IPECs have attracted
considerable attention during the recent years.
Because the micelles generated by ionic amphiphilic diblock copolymers in
aqueous media possess polyelectrolyte coronas, they are naturally expected to
form IPECs with oppositely charged polyions. To the best of our knowledge, the
first attempt to study interpolyelectrolyte complexation in such systems was
performed by Talingting et al. [59], who reported a study on the interaction of
protonated polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VPH
þ ) micelles with
linear PSSNa of different molecular weights. Under a considerable excess of
PSSNa to avoid any bridging or aggregation by linear polyions, the formation
of macromolecular co-assemblies with a large mass excess (by a factor of ca.
5–6) of the charged groups of the PSSNa over charged groups of P2VPH
þ was
found, thereby leading to charge inversion of the PS-b-P2VPH
þ micelles. This
concomitant massive charge overcompensation resulting from the considerable
molar excess (ca. 4.7–5.5) of sulfonate groups over pyridinium ones causes the
formed IPECs to be colloidally stable.
Water-soluble (or colloidally stable) IPECs formed by oppositely charged
micelles with polyelectrolyte coronas and linear polyions were subsequently
found for a number of other systems. In particular, a detailed characterization of
such macromolecular co-assemblies was performed for polyisobutylene-block-poly
(sodium methacrylate) (PIB-b-PMANa) micelles complexed with a linear P4VPQ
[60–62]. It was found that the formed IPECs remain water-soluble only when
loading of the original micelles (acting as a HPE) by the linear polyion (acting as
a GPE) does not exceed a certain threshold value. Such nonstoichiometric IPECs
were thoroughly examined by means of various techniques, which provided evidence on their peculiar core–shell–corona (also referred to as “onion-like”) structure (Fig. 10a). Specifically, each of the complex species comprises a hydrophobic
core from nonpolar blocks, which is surrounded by a layer (inner shell) assembled
from oppositely charged segments of the polymeric counterparts, and a hydrophilic
corona (outer shell) from excess segments of ionic blocks, which do not form
interpolymer salt bonds.
A similar multilayer structure with an inner complex shell was also proposed
for IPECs formed by PS-b-P4VPQ, PS-b-PANa, and PS-b-PMANa micelles
complexed with oppositely charged linear polyions [63–65]. In these cases, a
polyelectrolyte corona is formed either by excess segments of ionic blocks of
the copolymer (no overcharging of the original micelles by the linear polymeric
counterpart) or by excess segments of the linear polyion (overcharging of the
original micelles by the linear polymeric counterpart), depending on the actual
ratio between molar concentrations of charged groups of the polymeric components
in the system.
Advanced Functional Structures Based on Interpolyelectrolyte Complexes
193