Ultrathin random copolymer-grafted layers for block copolymer self-assembly

Area of Science:

• Polymer Science
• Materials Science
• Surface Chemistry

Background:

• Block copolymer (BCP) thin films are crucial for nanotechnology.
• Controlling nanodomain orientation on surfaces is challenging.
• Grafting polymers can modify surface properties.

Purpose of the Study:

• Investigate the effect of grafted random copolymers on BCP nanodomain orientation.
• Determine the critical thickness of grafted layers for perpendicular orientation.
• Understand the mechanism of surface neutralization and orientation control.

Main Methods:

• Grafting hydroxyl-terminated P(S-r-MMA) random copolymers (RCPs) onto silicon oxide.
• Studying cylinder-forming PS-b-PMMA block copolymer thin films on grafted surfaces.
• Analyzing nanodomain orientation as a function of grafted layer thickness (H) and RCP molecular weight (Mn).

Main Results:

• Perpendicular nanodomain orientation observed for grafted layers > 5-6 nm.
• For thinner layers (< 5 nm), orientation depends on RCP Mn.
• A 2.0 nm thick RCP layer (Mn=1700) was sufficient for perpendicular PMMA cylinder orientation.

Conclusions:

• Grafted RCPs effectively decouple BCPs from polar SiO2 surfaces.
• A proximity shielding mechanism, driven by RCP chain stretching, explains orientation control.
• Tailoring grafted layer properties allows precise control over BCP nanostructure formation.