(338n) Hiking the Energy Landscape for Block Copolymers Via Sequential Solvent Immersion and Thermal Processing for Versatile Self-Assembly

The kinetics and morphology of block copolymer (BCP) self-assembly in thin films significantly depends on the processing environment, which may include thermal annealing (TA), solvent vapor annealing (SVA), and direct immersion annealing (DIA). 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 unique kinetically trapped microstructures. Here we demonstrate a combinatorial DIA and TA method, where an instantaneous DIA rapidly induces weak parallel lamellar ordering with reduced domain sizes (metastable state) that rapidly transforms into standard TA equilibrium domain structures when subjected to TA. Overall, the cascaded DIA to TA shows much faster processing kinetics than TA alone for a similar degree of order. The reverse ordering process of TA followed by DIA, on the other hand, shows very different kinetics and morphology evolution, with highly irregular intermediate structures but with the same final state of DIA metastable structure. Swelling of the TA microstructure induces surface instability that hinders this transformation to the metastable state. This surface instability produces highly undulating topography and large surface areas. Considering the structural crossovers observed, a chain rearrangement mechanism for transition between the two distinct morphologies is proposed. 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 cascaded methods can be used for the rapid ordering of very low and high molecular weight BCP films that are difficult to process due to poor incompatibility or slower kinetics, respectively. These methods also allow us to access and probe intermediate microstructures with large surface areas.