3 research outputs found
Kinetics of Block Copolymer Phase Segregation during Sub-millisecond Transient Thermal Annealing
Early stage phase segregation of
block copolymers (BCPs) critically
impacts the material’s final structural properties, and understanding
the kinetics of these processes is essential to intentional design
of systems for practical applications. Using sub-millisecond lateral
gradient laser spike annealing and microbeam grazing incidence small-angle
X-ray scattering, the ordering and disordering kinetics of cylinder
forming polyÂ(styrene-<i>b</i>-methyl methacrylate) (PS-<i>b</i>-PMMA) were determined for peak annealing temperatures
up to 550 °C for dwells (anneal durations) ranging from 250 μs
to 10 ms. These temperatures, far in excess of the normal thermal
decomposition limit, are enabled by the short time scales of laser
annealing. From initially microphase-segregated films, disordering
was observed near the equilibrium order–disorder transition
temperature (<i>T</i><sub>ODT</sub>) for dwell times above
10 ms but was kinetically delayed by diffusion for shorter time scales,
resulting in suppression of observed disordering by over 70 °C.
The onset of ordering from initially disordered films was also kinetically
limited for short dwells. For anneals with peak temperatures well
above <i>T</i><sub>ODT</sub>, the block copolymer fully
disorders and quenches to a history-independent final state determined
by the quench rate. This kinetic behavior can be represented on an
effective <i>T</i><sub>g</sub> and <i>T</i><sub>ODT</sub> phase map as a function of the heating time scale. These
results then potentially enable BCP processing to retain or intentionally
modify the initial state while accelerating kinetics for other chemical
or structural alignment processes