Patterning with block copolymer blends

At the same time, based on the microphase separation occurring in block copolymers blends, including the latter may result in phase separated films exhibiting nano-domains. The formation of nanostructured domains at the interface induced by surface segregation of block copolymers is an interesting strategy to fabricate surfaces with controlled functionality and patterned in one single step. 

Reproduced with permission from H. Park, J.U. Kim, S. Park, High-throughput preparation of complex multi-scale patterns from block copolymer/homopolymer blend films, Nanoscale 4 (2012) 1362-1367. 

Alignment of perpendicular cylinders has been achieved using two methods. Treatment of substrates with PS-r-PMMA random copolymers bmshes to neutralize surface interaaions allows formation of perpendicular cylinders of PS-b-PMMA (PMMA cylinders). " Alternatively, block copolymers blended with homopolymers or other block copolymers are found to lead to perpendicular alignment for incommensurate film thicknesses when confined in patterns on substrates further alignment of the perpendicular cylinders is observed. 

In the PS/PMMA system it was possible to consistently replicate lines (uniform and nonimiform) and dots with sizes from 100 to 300 nm. Excellent replication of 30,45,60,90, and 135° angles in lines with widths from 100 to 300 run was also demonstrated. These results represent smaller nanoscale features and more complex nonuniform geometries than have previously been reported utilizing polymer blends. Block copolymers can also replicate these angles but require the use of a homopolymer. Patterning of a range of sizes is also challenging. ... 

Provided a large difference in molecular weight between the block copolymer and the matrix, we have to take into account that the relative ratio between the segments in the block copolymer plays an important role in the final morphology. As depicted in Fig. 5.16, typically, for AB block copolymers with similar volumes of block A and B we observe the formation of a lamellar phase that turns into a so-called onion ring pattern when blended with a A homopolymer. On the contrary, asymmetric block copolymers with larger A block tend to produce micellar aggregates randomly distributed in the homopolymer phase. 

The use of more complex systems such as ternary blends allows the functionalization of the surfaces with varies chemical functionalities. For instance a PS matrix was mixed with two block copolymers, a hydrophobic (PS-b-P5FS) and an amphiphilic polystyrene-b-poly[poly(ethylene glycol) methyl ether methacrylate] (PS-6-P(PEGMA)) copolymer [96], The chemical distribution of the resultant surface pattern implies an enrichment of the holes in the amphiphilic copolymer with an external surface mainly functionalized in the fluorinated copolymer with low surface energy (Scheme lO.lg). Other ternary blends combining incompatible copolymers and homopolymers have been reported leading to more complex topographies and chemical distributions [148],... 

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