Thickness-induced morphology changes in lamellar diblock copolymer ultrathin films
The James Franck Institute and Department of Physics,
The University of Chicago,
Chicago, Illinois 60637, USA
Accepted: 5 November 1997
We have investigated the morphology of lamellar polystyrene-polymethylmetha cry late diblock copolymers in the ultrathin-film limit, spin-cast and annealed on silicon nitride substrates. Our experiments show evidence for a morphology change from lamellar domains parallel to the substrate to perpendicular domains that appears to be unique to a thickness of one lamellar repeat spacing and low annealing temperatures. We find that in these ultrathin films phase separation occurs well before thickness quantization, suggesting effective confinement as a possible mechanism. A model for the free energy of this system is developed which takes into account termination ("capping") of the perpendicular lamellae inside the film and at its top surface.
PACS: 61.41.+e – Polymers, elastomers, and plastics / 68.55.Jk – Structure and morphology; thickness / 68.10.Cr – Surface energy (surface tension, interface tension, angle of contact, etc.)
© EDP Sciences, 1997