Morphology Development of Ultrathin Symmetric Diblock Copolymer Film via Solvent Vapor Treatment

Abstract

We have followed the time development of the microdomain structure in symmetric diblock copolymer poly(styrene-b-methyl methacrylate), P(S-b-MMA), ultrathin films via PMMA-selective solvent vapor treatment by atomic force microscopy (AFM). After preparation on a substrate preferentially attracting the PMMA block, PS forms a continuous layer at a film's free surface. With subsequent solvent vapor treatment, the film gradually shows a well-ordered hexagonally packed nanocylinders structure. It is shown that only when the film thickness is less than the 1 /2L0 (lamellar repeat spacing), and exposed to PMMA block selective solvent for an appropriate time, can the well-ordered hexagonally packed nanocylinders form. On an extended solvent vapor treatment, a mixed morphology containing nanocylinders and stripes appears, followed by the striped morphologies. When the annealing time is long enough, the film comes back to the flat surface again, however, with PMMA instead of PS dominating the free surface. Thickness confinement and solvent induced reconstruction of the film are shown to be responsible for the P(S-b-MMA) morphology and surface chemistry development.

Microdomain Orientation of PS-b-PMMA by Controlled Interfacial Interactions

“…22,23 This strategy has been achieved by surface modification, 24,25 strong electric field, 26,27 and solvent annealing. 28,29 Potentially the most robust of these strategies is surface modification via a neutral or nonpreferential wetting of the substrate, enabling A-b-B block copolymer to promote microdomain orientation perpendicular to the film surface by the balanced interfacial interaction, which is precisely tunable by the relative composition of A-r-B random copolymer on the substrate. 25,[30][31][32] By varying the composition of the random copolymers, surface properties ranging from PS to PMMA characteristics were observed from the dewetting behaviors of PS and PMMA, resulting that the interfacial energies on the substrate were balanced at an approximate styrene fraction of 0.58 in the P(S-r-MMA).…”

Nanopatterns Produced by Directed Self-Assembly in Block Copolymer Thin Films

“…In general, however, the solvent used is not genuinely neutral, which would usually lead to kinetically trapped nanostructures and alignments, especially if one or both blocks are glassy at room temperature [60]. Such metastability makes it possible to force the alignment of the nanostructures without tuning the energy balance, and the glassy nature of the final film insures the long-term absence of evolution of the pattern.…”

Creation of lateral structures in diblock copolymer thin films during vapor uptake and subsequent drying – Effect of film thickness

“…for their use in organized inorganic substrates [3,4] and for the preparation of nanoporous membranes [5,6]. Solvent vapor induced annealing offers a simple and flexible method to create ordered structures with a potentially high degree of controllability through careful choice of solvent [7][8][9][10][11][12][13][14][15][16].…”