Interplay of electrohydrodynamic structure formation and microphase alignment in lamellar block copolymers

Abstract

Electrohydrodynamic (EHD) destabilisation of a lamellar-forming block-copolymer (BCP) film gives rise to hierarchical pattern formation on the micrometre and 10 nm length scale in one single step. Two BCP morphologies were found in the columns that formed from a homogeneous surface instability. At low electric field strength, coaxial concentric lamellae indicate the dominance of surface tension differences of the BCP components over electric field effects. Outward opening lamellae are caused by lateral electric field gradients at sufficiently high field strength. Nucleated instabilities at low field strength give rise to stable bulls-eye-type ring structures consisting of BCP lamellae aligned along the ring perimeter. This is explained in terms of a free energy argument, illustrating the role of the internal energy of the BCP stack, resisting the deformation of the ring. Finally, the EHD experimental configuration was used to fabricate large monodomains of standing oriented lamellae.