of PS of 36 mN/m rather than 44 mN/m for PEO. Reversible switching of surface
properties was realized by repeated solvent treatment. DMF turned out to be a
suitable polar solvent, which may be related to its high boiling point of 153
C,
roughly 50
C above the T g of PS. The samples were deposited in DMF under reflux
and subsequent contact angle measurements showed a decreased contact angle of
68
, indicating a regression of the mixed polymer brushes at the topmost layer,
similar to the initial state.
In summary, the surface wetting shows reversible stimuli-responsive behavior
when applying external stimuli (e.g., temperature and solvent), as observed via
contact angle measurements. A contact angle shift of up to 23
from 61
to 84
and
vice versa was observed after heating and DMF treatment, respectively (Fig. 61b).
The role of the pre-organization of the amphiphilic block copolymers in solution
prior to the surface attachment, the potential of the materials with respect to achievable film thicknesses, and larger contact angle changes to switch wettability are
further intriguing issues based on the structural principle of amphiphilic junctionpoint reactive block copolymers. In addition, hydrolytic crosslinking of the TEOS
moieties in organized solution structures, such as block copolymer vesicles
(cf. Sect. 5.3) at the interface may be employed to stabilize “polymersome”-type
assemblies. At present, the concept of junction-point reactive block copolymers is
extended to other amphiphilic block copolymers with potential use for self-cleaning,
anti-fouling, and friction-reducing ultrathin polymer layers.
5.3 Nanoparticles Confined in a Polymersome Shell Layer
Amphiphilic block copolymers self-assemble in selective solvents such as water.
Depending on parameters like overall average molecular weight, volume fraction of
each block, or effective interaction energy between monomers in the blocks, vesicles
with a bilayer shell and a solvent interior volume similar to liposomes are formed.
They are often called polymersomes [241]. Such polymersomes in aqueous media
have attracted increasing interest due to their enhanced stability compared to classical
liposomes and due to the potential to control vesicle properties like bilayer thickness,
permeability, or surface functionalities by appropriate chemical copolymer
adjustment [242].
The block copolymer polybutadiene-block-poly(ethylene oxide) (PB-b-PEO) is
frequently studied because it offers several advantages [243–246]. For example, the
PEO that forms the outer part of the assembled structures in water is generally
regarded as biocompatible [247, 248]. Furthermore, depending on the PB block
length, the assembled polymersomes can exhibit a thicker hydrophobic membrane
core and therefore higher stability compared to liposomes [249]. Additionally, this
copolymer features the possibility to crosslink the PB part and thereby stabilize the
assembled structure [250–252].
Amphiphilic block copolymers have been suggested as drug carriers. The
concept of drug delivery is based on successful encapsulation of substrates with
188
K. Binder et al.
properties was realized by repeated solvent treatment. DMF turned out to be a
suitable polar solvent, which may be related to its high boiling point of 153
C,
roughly 50
C above the T g of PS. The samples were deposited in DMF under reflux
and subsequent contact angle measurements showed a decreased contact angle of
68
, indicating a regression of the mixed polymer brushes at the topmost layer,
similar to the initial state.
In summary, the surface wetting shows reversible stimuli-responsive behavior
when applying external stimuli (e.g., temperature and solvent), as observed via
contact angle measurements. A contact angle shift of up to 23
from 61
to 84
and
vice versa was observed after heating and DMF treatment, respectively (Fig. 61b).
The role of the pre-organization of the amphiphilic block copolymers in solution
prior to the surface attachment, the potential of the materials with respect to achievable film thicknesses, and larger contact angle changes to switch wettability are
further intriguing issues based on the structural principle of amphiphilic junctionpoint reactive block copolymers. In addition, hydrolytic crosslinking of the TEOS
moieties in organized solution structures, such as block copolymer vesicles
(cf. Sect. 5.3) at the interface may be employed to stabilize “polymersome”-type
assemblies. At present, the concept of junction-point reactive block copolymers is
extended to other amphiphilic block copolymers with potential use for self-cleaning,
anti-fouling, and friction-reducing ultrathin polymer layers.
5.3 Nanoparticles Confined in a Polymersome Shell Layer
Amphiphilic block copolymers self-assemble in selective solvents such as water.
Depending on parameters like overall average molecular weight, volume fraction of
each block, or effective interaction energy between monomers in the blocks, vesicles
with a bilayer shell and a solvent interior volume similar to liposomes are formed.
They are often called polymersomes [241]. Such polymersomes in aqueous media
have attracted increasing interest due to their enhanced stability compared to classical
liposomes and due to the potential to control vesicle properties like bilayer thickness,
permeability, or surface functionalities by appropriate chemical copolymer
adjustment [242].
The block copolymer polybutadiene-block-poly(ethylene oxide) (PB-b-PEO) is
frequently studied because it offers several advantages [243–246]. For example, the
PEO that forms the outer part of the assembled structures in water is generally
regarded as biocompatible [247, 248]. Furthermore, depending on the PB block
length, the assembled polymersomes can exhibit a thicker hydrophobic membrane
core and therefore higher stability compared to liposomes [249]. Additionally, this
copolymer features the possibility to crosslink the PB part and thereby stabilize the
assembled structure [250–252].
Amphiphilic block copolymers have been suggested as drug carriers. The
concept of drug delivery is based on successful encapsulation of substrates with
188
K. Binder et al.