Porous Block Copolymer Film Templates

Hereafter, electrochemical growth of new material in the pores of the film is reliant on optimizing many of the same parameters demanded by other nanoporous electrode structures, such as anodized alumina and track-etched membranes [45]. 

A summary of the reported, selectively sacrificial diblock copol5miers and relevant etching methods used to produce porous materials is shown in Table 2.1. Rather few of these systems have yet been explored as electrochemical film templates, largely 

So far the most widely studied copol miers studied as precursors for porous electrochemical film templates are poly PS-h-PMMAand PFS-h-PLA. 

Poly(lactic acid) presents a particularly interesting sacrificial copolymer component as it is very simple to degrade under mild chemical conditions—namely soaking the material in a 0.05 M NaOH(aq) solution [49]. In PFS-6-PLA, the fluorinated styrene majority block is intended to improve the dielectric contrast between the two blocks for ease of electric field alignment in comparison to the more widely available poly(st50 ene-6-poly(lactide) (PS-b-PLA) [56], 

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In 2004, Olayo-Valles et al. described a related dry-etch processing of self-assembled block copolymer films to generate porous materials for use as magnetic material templates [50]. These authors employed thin films of... 

Fig. 9 Schematic representation of three approaches to generate nanoporous and meso-porous materials with block copolymers, a Block copolymer micelle templating for mesoporous inorganic materials. Block copolymer micelles form a hexagonal array. Silicate species then occupy the spaces between the cylinders. The final removal of micelle template leaves hollow cylinders, b Block copolymer matrix for nanoporous materials. Block copolymers form hexagonal cylinder phase in bulk or thin film state. Subsequent crosslinking fixes the matrix hollow channels are generated by removing the minor phase, c Rod-coil block copolymer for microporous materials. Solution-cast micellar films consisted of multilayers of hexagonally ordered arrays of spherical holes. (Adapted from [33])...

Back-filling pores formed by the selective removal of one block of an assembled block copolymer (described above) has also yielded a variety of patterned materials. All examples use one of the porous templates fabricated from self-assembled block copolymer films described above in Section 8.02.3.1.1. In some cases, the polymer template is subsequently removed in other cases, the polymer template is left in place. 

Fig. 10 Schematic representation of the nanoreplication processes from block copolymers, a Growth of high-density nanowires from a nanoporous block copolymer thin film. An asymmetric PS-fc-PMMA diblock copolymer was aligned to form vertical PMMA cylinders under an electric field. After removal of the PMMA minor component, a nanoporous film is formed. By electrodeposition, an array of nanowires can be replicated in the porous template (adapted from [43]). b Hexagonally packed array of aluminum caps generated from rod-coil microporous structures. Deposition of aluminum was achieved on the photooxidized area of the rod-coil honeycomb structure (Taken from [35])...

Figure 2.13 Schematic illustration of the process of fabricating a porous PANI-NF film by a galvanostatic method using porous poly(styrene-block-2-vinylpyridine) diblock copolymer films as templates. (Reprinted with permission from Langmuir, One-Step Route to the Fabrication of Highly Porous Polyaniline Nanofiber Films by Using PS-b-PVP Diblock Copolymers as Templates by X. Li, S. Tian, Y. Ping et ai, 2 , 2 , 9393-9397. Copyright (2005) American Chemical Society)...

Apart from the use of block copolymers providing nanoscale features other methodologies alone or in combination can provide hierarchically stmctured patterns. For instance taking advantage of the template assisted stmcturation, demixing of polymer blend solutions on stmctured substrates can also be employed to create multiscale ordered surfaces. Boneberg et al. [202] employed this approach and blended two components, PVP and PS, already known to form ordered porous films during phase separation [203]. The authors used a micrometer patterned... 

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