in-chain attachment and self-assembly of a block copolymer on a surface. As a third
example we describe the inverse effect: vesicles formed by block copolymers and
dispersed in aqueous medium confine quantum dots in the hydrophobic interior of
the lamellae.
5.1 Diblock Copolymers Confined in Miniemulsion Droplets
As a first example, we consider block copolymers confined in droplets as obtained
by the miniemulsion process. It is well known that block copolymers self-assemble
into periodic nanostructures such as lamellae, hexagonally coordinated cylinders,
cubic lattices of spheres, and the gyroid morphology [189, 211]. This phase
behavior can be adjusted by different parameters such as temperature or the
chemical composition [212, 213]. Block copolymers have been investigated
extensively in bulk. The influence of a 2D or 3D confinement on the sub-100-nm
scale has, however, only been examined in a limited way. In the 2D confinement of
a film, a deviation of the lamellar thickness from the value of the bulk material is
induced [214]. By confining a block copolymer in a porous silica matrix, both
cylindrical and lamellar structures were observed [215]. Electrospinning and
subsequent annealing of the obtained fibers also lead to cylindrical structures
[216]. Onion-like block copolymer morphologies were obtained in spherical
particles using spray coating [217]. Using emulsion techniques and subsequent
solvent evaporation techniques, onion-like particles from poly(styrene-b-isoprene)
and poly(styrene-b-methyl methacrylate) (PS-b-PMMA) were created
[218]. Lamellar, hexagonal, and bicontinuous phases in nanoparticles could be
realized with a triblock copolymer [219].
Nanoparticles consisting of different molecular weight PS-b-PMMA copolymers
and nanocapsules made of the same copolymers, but additionally with hexadecane as
liquid core material, were prepared by using a combined miniemulsion and solvent
evaporation technique [220]. The morphology of block copolymer assemblies was
investigated in dependence of the nanoconfinement. We introduced two
nanoconfinement parameters: the diameter D of the droplet throughout the synthesis
and the shell thickness δ of the nanocapsules with a liquid as core. D was controlled
by varying the concentration of the surfactant in the miniemulsion, while δ was
controlled by the ratio of hexadecane to copolymer.
For the investigation of the influence of the molecular weight of the polymer on
the morphology of the block copolymer, we used PS 76 -b-PMMA 79 and PS 838 -bPMMA 945 , where the numbers correspond to the average numbers of units of
styrene and methylmethacrylate [221].
For the formation of solid copolymer nanoparticles without a liquid core, PS-bPMMA was used as a model system. In order to be able to form nanoparticles, the
block copolymer was dissolved in chloroform and the solution was miniemulsified
in water by adding the SDS. In this case, homogeneous droplets were formed. After
evaporation of the chloroform, nanoparticles consisting entirely of block copolymer
Structure Formation of Polymeric Building Blocks: Complex Polymer Architectures
177
example we describe the inverse effect: vesicles formed by block copolymers and
dispersed in aqueous medium confine quantum dots in the hydrophobic interior of
the lamellae.
5.1 Diblock Copolymers Confined in Miniemulsion Droplets
As a first example, we consider block copolymers confined in droplets as obtained
by the miniemulsion process. It is well known that block copolymers self-assemble
into periodic nanostructures such as lamellae, hexagonally coordinated cylinders,
cubic lattices of spheres, and the gyroid morphology [189, 211]. This phase
behavior can be adjusted by different parameters such as temperature or the
chemical composition [212, 213]. Block copolymers have been investigated
extensively in bulk. The influence of a 2D or 3D confinement on the sub-100-nm
scale has, however, only been examined in a limited way. In the 2D confinement of
a film, a deviation of the lamellar thickness from the value of the bulk material is
induced [214]. By confining a block copolymer in a porous silica matrix, both
cylindrical and lamellar structures were observed [215]. Electrospinning and
subsequent annealing of the obtained fibers also lead to cylindrical structures
[216]. Onion-like block copolymer morphologies were obtained in spherical
particles using spray coating [217]. Using emulsion techniques and subsequent
solvent evaporation techniques, onion-like particles from poly(styrene-b-isoprene)
and poly(styrene-b-methyl methacrylate) (PS-b-PMMA) were created
[218]. Lamellar, hexagonal, and bicontinuous phases in nanoparticles could be
realized with a triblock copolymer [219].
Nanoparticles consisting of different molecular weight PS-b-PMMA copolymers
and nanocapsules made of the same copolymers, but additionally with hexadecane as
liquid core material, were prepared by using a combined miniemulsion and solvent
evaporation technique [220]. The morphology of block copolymer assemblies was
investigated in dependence of the nanoconfinement. We introduced two
nanoconfinement parameters: the diameter D of the droplet throughout the synthesis
and the shell thickness δ of the nanocapsules with a liquid as core. D was controlled
by varying the concentration of the surfactant in the miniemulsion, while δ was
controlled by the ratio of hexadecane to copolymer.
For the investigation of the influence of the molecular weight of the polymer on
the morphology of the block copolymer, we used PS 76 -b-PMMA 79 and PS 838 -bPMMA 945 , where the numbers correspond to the average numbers of units of
styrene and methylmethacrylate [221].
For the formation of solid copolymer nanoparticles without a liquid core, PS-bPMMA was used as a model system. In order to be able to form nanoparticles, the
block copolymer was dissolved in chloroform and the solution was miniemulsified
in water by adding the SDS. In this case, homogeneous droplets were formed. After
evaporation of the chloroform, nanoparticles consisting entirely of block copolymer
Structure Formation of Polymeric Building Blocks: Complex Polymer Architectures
177