-PMMA block copolymer thin films*

The grain coarsening in thin films (~30 nm) of cylinder forming PS-b-PMMA BCP (N=379-1281) was accomplished by tuning of the annealing temperature and time in a RTP machine. The order of the hexagonal pattern was quantified by measuring the correlation length.
The weakly dependence on T of χ_S-MMA allows decoupling the control of χN by means of N, and that of the thermally activated kinetic barriers for ordering kinetics modulating T, evidencing the order-disorder transition (ODT) and glass transition (GT) involved in BCP ordering.
Thermodynamically, weak and strong segregation limits are not distinguishable. In weak segregation limit the ordering process switches from a diffusion limited to a curvature driven mechanism. Both single chain and collective motions comply with the extensively evidenced kinetic limited coarsening and the reduced diffusivity, increasing N and moving away from ODT, and with the thermodynamic limited coarsening and the enhanced diffusivity, decreasing N and moving towards ODT.
The collective dynamic is further investigated discriminating the behavior of the penta-hepta defects within the hexagonal pattern to give a comprehensive description of thermodynamic, kinetic and topological characteristics of the hexagonal pattern coarsening.