As cryogenic TEM imaging does not necessarily represent the entire sample,
FCS measurements (data not shown) were performed additionally for measuring
diffusion coefficients of fluorescent particles [271, 276–280]. Light scattering
yields a hydrodynamic radius of R h ¼ 67 nm, which describes the average of the
whole sample content. Nevertheless, the result is in good agreement with FCS,
which yields R h ¼ 62 nm detecting only the fluorescent sample content (in our case
the loaded polymersomes). Both results are comparable to those observed with
cryogenic TEM; two examples are shown in Fig. 66a, b. The agreement of DLS and
FCS results shows that Nile Red and QDs were successfully incorporated into the
hydrophobic part of the polymersomes.
In conclusion, the hydrophobic shell of PB-b-PEO polymersomes was successfully
loaded with the fluorescent dye Nile Red and highly fluorescent QDs as hydrophobic
model substrates. FCS showed that fluorescing signals belong to the diffusion
of fluorescently loaded vesicles only, demonstrating that no other aggregation or
structure stabilization occurred. Cryogenic TEM and fluorescence microscopy
imaging confirmed that the hydrophobic substrates were enclosed inside the hydrophobic polymersome shell. In the case of the QD-loaded polymersomes, it has been
possible by cryogenic TEM imaging to prove that the QD are located in between
the two hydrophobic PB layers of the shell bilayer, introducing curvature of the
copolymer layers around the guest particles. The combination of independent methods
of characterization made it possible to successfully investigate the localization of the
hydrophobic substrates within the hydrophobic shell of the polymersomes. Further
experiments with differently sized nanoparticles will determine the limits for particle
enclosing and confinement inside the shell, revealing how far the double-layer can
curve before different structural assemblies are favored. Furthermore, these
experiments can be nicely linked to the results obtained in other particle systems
or confinement of nanoparticles in planar surfaces, as discussed in the other parts of
this chapter.
5.4 Conclusion
The process of formation of complex block copolymer structures in 3D confinement
has been elucidated for some selected PS-b-PMMA copolymers. Introduction of a
nonsolvent into the spherical nanoparticles yielded hemispherical structures of onionlike morphology. Such structures may be viewed as a result of double confinement
consisting of the outer surfactant double layer and the inner nanophase separation
between the block copolymer and the nonsolvent for both blocks. This concept allows
targeting the nanoparticle shape as well as the inner particle morphology (ranging
from simple core–shell to onion-like to patched structures), which may find application for encapsulation of various substrates with predetermined release characteristics.
Regarding 2D confinement, newly synthesized “junction-point” block copolymers
were chemically anchored onto planar substrates by their reactive junction-point
moiety, forming a smooth monomolecular layer. By thermal treatment or exposure
Structure Formation of Polymeric Building Blocks: Complex Polymer Architectures
193
FCS measurements (data not shown) were performed additionally for measuring
diffusion coefficients of fluorescent particles [271, 276–280]. Light scattering
yields a hydrodynamic radius of R h ¼ 67 nm, which describes the average of the
whole sample content. Nevertheless, the result is in good agreement with FCS,
which yields R h ¼ 62 nm detecting only the fluorescent sample content (in our case
the loaded polymersomes). Both results are comparable to those observed with
cryogenic TEM; two examples are shown in Fig. 66a, b. The agreement of DLS and
FCS results shows that Nile Red and QDs were successfully incorporated into the
hydrophobic part of the polymersomes.
In conclusion, the hydrophobic shell of PB-b-PEO polymersomes was successfully
loaded with the fluorescent dye Nile Red and highly fluorescent QDs as hydrophobic
model substrates. FCS showed that fluorescing signals belong to the diffusion
of fluorescently loaded vesicles only, demonstrating that no other aggregation or
structure stabilization occurred. Cryogenic TEM and fluorescence microscopy
imaging confirmed that the hydrophobic substrates were enclosed inside the hydrophobic polymersome shell. In the case of the QD-loaded polymersomes, it has been
possible by cryogenic TEM imaging to prove that the QD are located in between
the two hydrophobic PB layers of the shell bilayer, introducing curvature of the
copolymer layers around the guest particles. The combination of independent methods
of characterization made it possible to successfully investigate the localization of the
hydrophobic substrates within the hydrophobic shell of the polymersomes. Further
experiments with differently sized nanoparticles will determine the limits for particle
enclosing and confinement inside the shell, revealing how far the double-layer can
curve before different structural assemblies are favored. Furthermore, these
experiments can be nicely linked to the results obtained in other particle systems
or confinement of nanoparticles in planar surfaces, as discussed in the other parts of
this chapter.
5.4 Conclusion
The process of formation of complex block copolymer structures in 3D confinement
has been elucidated for some selected PS-b-PMMA copolymers. Introduction of a
nonsolvent into the spherical nanoparticles yielded hemispherical structures of onionlike morphology. Such structures may be viewed as a result of double confinement
consisting of the outer surfactant double layer and the inner nanophase separation
between the block copolymer and the nonsolvent for both blocks. This concept allows
targeting the nanoparticle shape as well as the inner particle morphology (ranging
from simple core–shell to onion-like to patched structures), which may find application for encapsulation of various substrates with predetermined release characteristics.
Regarding 2D confinement, newly synthesized “junction-point” block copolymers
were chemically anchored onto planar substrates by their reactive junction-point
moiety, forming a smooth monomolecular layer. By thermal treatment or exposure
Structure Formation of Polymeric Building Blocks: Complex Polymer Architectures
193