In block copolymer (BCP) lithography the periodicity or dimensions of a patterned template are amplified by assembling a BCP on top of the chemical or topographical pattern. The potential for this technology has driven the preparation of a variety of novel chemistries and architecture in order to optimize the assembly thermodynamics. Bottlebrush block copolymers (BBCPs) are intriguing options given their high entanglement weights and therefore rapid self-assembly. However, there are limited studies of their assembly into thin films. Using a combination of scattering measurements and atomic force microscopy we demonstrate that the periodicity of a BBCP confined to a thin film is thickness dependent. Samples with a thickness gradient were prepared using blade coating and measured at regular intervals along the gradient. As the thickness decreased the periodicity increased, up until the estimated full extension of the BBCP backbone. Changing the affinity of the solvent for the two components also drives a change in the morphology of the film, in one case driving the formation of a mixed morphology of cylinders and lamellae. The thickness dependence of the periodicity bears a strong resemblance to the extension of DNA in solution when confined to a channel, and the comparison between these systems will be discussed.

The influence of confinement on the self-assembly of bottlebrush block copolymers

ACS Spring Meeting 2021

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