2.3 Patterned Organic and Polymeric Films for Tailored (Bio)Interfaces
39
and the order to disorder transition for the diblock copolymer can be predicted.
Normally, the domain interfaces are sharp in the strong segregation limit ((χN) ODT >
10) and more diffuse in the weak segregation limit. The morphologies of microphase
separation formed by diblock copolymers are well-understood by now. Typical examples for the morphologies of diblock copolymers are depicted in Fig. 2.23. These
include alternating lamellae (LAM), hexagonally (HEX) packed cylinders, bicontinuous gyroid, and body-centered cubic-packed spheres (BCC). Here, the bicontinuous
gyroid phase will appear especially near the order/disorder transition. In the strong
segregation limit, i.e., at large values for χN, the volume fractions for the transitions
between the different ordered phases are almost independent of χN or temperature.
2.3.4.3 Applications
Block copolymers are complex, soft materials that have been used in diverse scientific
and technological applications. They have been employed to understand interesting
and broadly important physical phenomena in ordered soft materials. Predictable
self-assembly and the wide array of accessible block structures have further enabled
scientific and technologically relevant advances using these materials. With respect
to the latter materials, block copolymers are arguably ideal precursors for the formation of ordered nanoporous organic polymers. The preparation of ordered nanoporous
polymers from block copolymer precursors was established in 1988 by Nakahama.
Nanoporous polymers can be prepared by several routes, such as controlled phase
separation, etching, and molecular imprinting. These materials with nanometer periodic patterning of block polymers are important due to their potential and established
utility as patterned media, catalysts transistor, nanowire and template for the growth
of nanoscopic materials, lithography templates, polymeric electrolytes, cell growth
control, sensors, and biomaterials.
Nanopatterns by diblock copolymers: Lammertink, Vacso et al. have
described the microphase-separated structures of organometallic poly(styrene-blockferrocenylsilane) (PS-b-PFS) diblock copolymers, which are attractive materials
because of the formation of metal-containing nanostructures upon phase separation.
They studied the phase-separated structures of (PS-b-PFS) copolymers as a function
of their block composition. By increasing the volume of PFS blocks in the copolymer,
the different morphologies from cylindrical to lamellar have been observed by TEM.
Morkved et al. have demonstrated the use of an in-plane electric field to uniformly
orient the cylindrical microdomains of PS-b-PMMA diblock copolymer film and
the clear observation of field-induced orientation in a large area thin film of asymmetric PS-b-PMMA diblock copolymer from small angle neutron scattering data.
The method uses a shear apparatus with certain frequency and amplitude to shear
the film along a certain direction, which can control anisotropic molecular orientations inside the ordered block copolymer mesophases. It will be potentially significant for novel technological applications. Using this method, Zhu et al. have
discussed nanoconfined polymer crystallization in a complex hexagonally perforated layer (HPL) phase in a poly(styrene-block-ethylene oxide) (PS-b-PEO) diblock
39
and the order to disorder transition for the diblock copolymer can be predicted.
Normally, the domain interfaces are sharp in the strong segregation limit ((χN) ODT >
10) and more diffuse in the weak segregation limit. The morphologies of microphase
separation formed by diblock copolymers are well-understood by now. Typical examples for the morphologies of diblock copolymers are depicted in Fig. 2.23. These
include alternating lamellae (LAM), hexagonally (HEX) packed cylinders, bicontinuous gyroid, and body-centered cubic-packed spheres (BCC). Here, the bicontinuous
gyroid phase will appear especially near the order/disorder transition. In the strong
segregation limit, i.e., at large values for χN, the volume fractions for the transitions
between the different ordered phases are almost independent of χN or temperature.
2.3.4.3 Applications
Block copolymers are complex, soft materials that have been used in diverse scientific
and technological applications. They have been employed to understand interesting
and broadly important physical phenomena in ordered soft materials. Predictable
self-assembly and the wide array of accessible block structures have further enabled
scientific and technologically relevant advances using these materials. With respect
to the latter materials, block copolymers are arguably ideal precursors for the formation of ordered nanoporous organic polymers. The preparation of ordered nanoporous
polymers from block copolymer precursors was established in 1988 by Nakahama.
Nanoporous polymers can be prepared by several routes, such as controlled phase
separation, etching, and molecular imprinting. These materials with nanometer periodic patterning of block polymers are important due to their potential and established
utility as patterned media, catalysts transistor, nanowire and template for the growth
of nanoscopic materials, lithography templates, polymeric electrolytes, cell growth
control, sensors, and biomaterials.
Nanopatterns by diblock copolymers: Lammertink, Vacso et al. have
described the microphase-separated structures of organometallic poly(styrene-blockferrocenylsilane) (PS-b-PFS) diblock copolymers, which are attractive materials
because of the formation of metal-containing nanostructures upon phase separation.
They studied the phase-separated structures of (PS-b-PFS) copolymers as a function
of their block composition. By increasing the volume of PFS blocks in the copolymer,
the different morphologies from cylindrical to lamellar have been observed by TEM.
Morkved et al. have demonstrated the use of an in-plane electric field to uniformly
orient the cylindrical microdomains of PS-b-PMMA diblock copolymer film and
the clear observation of field-induced orientation in a large area thin film of asymmetric PS-b-PMMA diblock copolymer from small angle neutron scattering data.
The method uses a shear apparatus with certain frequency and amplitude to shear
the film along a certain direction, which can control anisotropic molecular orientations inside the ordered block copolymer mesophases. It will be potentially significant for novel technological applications. Using this method, Zhu et al. have
discussed nanoconfined polymer crystallization in a complex hexagonally perforated layer (HPL) phase in a poly(styrene-block-ethylene oxide) (PS-b-PEO) diblock