Phase transition behavior in thin films of block copolymers by use of immiscible solvent vapors

Abstract

The phase transitions in thin films of a block copolymer, BCP, that forms micelles when exposed to immiscible solvent vapors, were investigated at two different temperatures. Pre-swelling with a nonvolatile solvent was used to prevent dewetting prior to the addition of a volatile solvent used to affect the annealing. The temperature and, therefore, the vapor pressure of the solvent were varied, which gave rise to remarkably different kinetic pathways of lateral ordering of the BCP. At 22 degrees C, a rapid annihilation of defects occurred with exchange of BCP chains between domains. At 17 degrees C, a slow coalescence of two adjacent domains led to enhanced lateral ordering of the swollen BCP microdomains and also led to domains twice as large as those observed at 22 degrees C. These studies suggest that the large interfacial energy arising from the immiscibility of the components, coupled with an incommensurability of the swollen film thickness with the period of the BCP morphology, gave rise to the observed differences and subsequent lateral ordering of the BCP microdomains.