Abstract
A variety of structures encountered in nature only arise in materials under highly nonequilibrium conditions, suggesting to us that the scope for creating new functional block copolymer (BCP) structures might be significantly enlarged by embracing complex processing histories that allow for the fabrication of structures quite unlike those created under “near-equilibrium” conditions. The present work examines the creation of polymer film structures in which highly nonequilibrium processing conditions allow for the creation of entirely new types of transient BCP morphologies achieved by transitioning between different ordered states. Most previous studies of BCP materials have emphasized ordering them from their disordered state obtained from a solution film casting process, followed by a slow thermal annealing (TA) process at elevated temperatures normally well above room temperature. We have previously shown that achieving the equilibrium TA state can be accelerated by a direct solvent immersion annealing (DIA) preordering step that creates nascent ordered microstructures, followed by TA. In the present work, we examine the reverse nonequilibrium sequential processing in which we first thermally anneal the BCP film to different levels of partial (lamellar) order and then subject it to DIA to swell the lamellae. This sequential processing rapidly leads to a swelling-induced wrinkle pattern that initially grows with immersion time and can be quenched by solvent evaporation into its corresponding glassy state morphology. The article demonstrates the formation of wrinkling “defect” patterns in entangled BCP films by this sequential annealing that does not form under ordinary TA conditions. At long DIA times, these highly “defective” film structures evolve in favor of the equilibrium morphology of parallel lamellae observed with DIA alone. In conjunction with our previous study of sequential DIA + TA, the present TA + DIA study demonstrates that switching the order of these processing methods for block copolymer films gives the same final state morphology in the limit of long time as any one method alone, but with drastically different intermediate transient state morphologies. These transient morphologies could have many applications.
Original language | English |
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Pages (from-to) | 15569-15585 |
Number of pages | 17 |
Journal | ACS Applied Materials and Interfaces |
Volume | 16 |
Issue number | 12 |
DOIs | |
State | Published - Mar 27 2024 |
Funding
We would like to acknowledge Dr. Tanguy Terlier at RICE University’s Shared Equipment Authority for time-of-flight secondary ion mass spectroscopy experiments to measure the initial stratification of domains after a short time of high-temperature thermal annealing. The measurements at Oak Ridge National Lab (ORNL), run by University of Tennessee-Battelle Memorial Institute (UT-Battelle), LLC, were performed under Contract No. DE-AC05-00OR22725 with the US Department of Energy. We acknowledge NSF DMR 1905996 for support of the research. Support from Welch Foundation via grants e-2105–20220331 and v-e-0003–20230731 is also acknowledged.
Funders | Funder number |
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Oak Ridge National Laboratory | |
U.S. Department of Energy | |
National Science Foundation | DMR 1905996 |
Welch Foundation | v-e-0003–20230731, e-2105–20220331 |
University of Tennessee-Battelle Memorial Institute | DE-AC05-00OR22725 |
Keywords
- block copolymers
- direct immersion annealing
- neutron reflectivity
- nonequilibrium
- order−order transition
- thermal annealing
- thin films
- wrinkling