MOLECULAR DYNAMICS SIMULATIONS OF LASER SPIKE ANNEALING OF BLOCK COPOLYMER THIN LAMELLAR FILMS
Recent experimental studies have reported that laser spike annealing (LSA) can accelerate the order-disorder transition "ODT" (for melting and reordering) of block copolymer thin films. With LSA the polymer is subjected to much higher temperatures but for a far shorter time compared to traditional thermal annealing, resulting in an induced disordering temperature that increases as the heating/cooling cycle decreases. Such a trend arises from the LSA time scale being shorter than the time scale for the ODT at the thermodynamic ODT temperature, but longer than the polymer relaxation time scale. In this work, we use molecular dynamic simulations of a simple coarse- grained model to study the phase behavior of a general lamella-forming A-b-B di- block copolymer thin film under different heating cycle lengths, film thickness, and substrate-polymer affinity. This model describes a realistic soft confinement scenario to study the effects of a free surface (air-polymer interface) and solid substrate selectivity on thin film morphology. Our simulation results successfully capture a similar trend for the ODT temperature as in LSA experiments (for comparable heating cycle lengths) when the vertical lamella phase formed on neutral substrates. In addition, simulations with a substrate selective for a particular block revealed the formation of a metastable island phase having horizontal but incomplete lamella layers. The nanoscale roughness features of this island phase could be of potential use to modulate the wettability of surfaces as the degree of roughness can be controlled to some extent with suitable choices of polymer chemistry and the annealing conditions.
Molecular physics; Polymer chemistry; Chemical engineering
Joo, Yong L.
M.S., Chemical Engineering
Master of Science
dissertation or thesis