15.5
Nanostructures Based on Bulk Phase Separation
Selective fixation of one of the domains in any of the morphologies formed by
block copolymers, either by polymerization or by photo-crosslinking, is an elegant
way to generate nanostructures. Utilizing such a concept, several types of nanosize
objects, such as nanospheres, nanofibres and nanotubes etc., have been successfully prepared. A schematic representation of this general methodology is shown
in Figure 15.5.
One of the very early examples of this concept for the generation of nanospheres
utilized a diblock copolymer-poly(styrene)-block-poly(4-vinyl pyridine), labeled PS-bP4VP [35]. Using a diblock copolymer with a higher weight-fraction of PS (>75
wt%), solvent cast films were shown to contain spherical micellar aggregates with a
P4VP core embedded in a PS matrix, as confirmed by TEM studies. Exposure of
these films to vapors of 1,4-dibromobutane (DBB), caused crosslinking of the PVP
Im3m
LAM
HPL
Ia3d
HEX
Spheres
Cylinders
Bicontinuous
Perforated
layers
Lamellae
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
f PI
40
30
20
10
0
χN
Disordered
HEX
HPL
LAM
la3d
HEX
la3m
-
-
Fig. 15.4. Various morphologies observed in phase-separated
diblock copolymers, along with the experimental phase portrait
for PI-b-PS diblock copolymer. (Reprinted with permission from
Macromolecules, 1995, 28, 8796 [33]. 8 1995 American
Chemical Society.)
15 Nanostructured Polymers
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