(167ai) Rapid Ordering of Block Copolymer Films By Sequential Solution Immersion and Thermal Annealing with Asymmetric Reversible Processing

The kinetics and morphology of block copolymer (BCP) assembly in thin films are highly dependent on processing pathways that may include thermal annealing (TA), solvent vapor annealing (SVA), direct immersion annealing (DIA), solvent evaporation annealing (SEA), and microwave annealing methods. Thus, it is only to be expected that sequential/parallel annealing of the same BCP film by two or more techniques can produce unique synergies of ordering kinetics, morphology evolution, and asymmetry in transition mechanisms. With this research we demonstrate a sequential DIA followed by TA method, where DIA rapidly produces weakly parallel metastable lamellar assembly with highly reduced domain sizes that rapidly transform into standard TA equilibrium domain structures when subjected to TA. Overall, the DIA plus TA method shows much faster processability kinetics than TA alone for a similar degree of ordering. We further studied the reverse ordering process of TA followed by DIA and observed very different kinetics and morphology evolution, but with the same final state of DIA equilibrium structure. A chain rearrangement mechanism between the two distinct morphologies and the effects of successive annealing processes in these self-assembled systems is proposed for the structural crossover, and the underlying dynamics of this reversibility process are analyzed in terms of chain swelling, diffusion, and in-plane vs. out-of-plane interfacial evolution. The transitions are populated on an energy landscape to elaborate upon the asymmetry in the reversible transitions.