Morphological Evolution of Gyroid-Forming Block Copolymer Thin Films with Varying Solvent Evaporation Rate

Abstract

In this study, we aim to examine the morphological evolution of block copolymer (BCP) nanostructured thin films through solvent evaporation at different rates for solvent swollen polystyrene-block-poly(l-lactide) (PS-PLLA). Interesting phase transitions from disorder to perpendicular cylinder and then gyroid can be found while using a partially selective solvent for PS to swell PS-PLLA thin film followed by solvent evaporation. During the transitions, gyroid-forming BCP thin film with characteristic crystallographic planes of (111)G, (110)G, and (211)G parallel to air surface can be observed, and will gradually transform into coexisting (110)G and (211)G planes, and finally transforms to (211)G plane due to the preferential segregation of constituted block to the surface (i.e., the thermodynamic origin for self-assembly) that affects the relative amount of each component at the air surface. With the decrease on the evaporation rate, the disorder phase will transform to parallel cylinder and then directly to (211)G without transition to perpendicular cylinder phase. Most importantly, the morphological evolution of PS-PLLA thin films is strongly dependent upon the solvent removal rate only in the initial stage of the evaporation process due to the anisotropy of cylinder structure. Once the morphology is transformed back to the isotropic gyroid structure after long evaporation, the morphological evolution will only relate to the variation of the surface composition. Similar phase transitions at the substrate can also be obtained by controlling the ratio of PLLA-OH to PS-OH homopolymers to functionalize the substrate. As a result, the fabrication of well-defined nanostructured thin films with controlled orientation can be achieved by simple swelling and deswelling with controlled evaporation rate.

Supramolecular Chirality Transfer toward Chiral Aggregation: Asymmetric Hierarchical Self‐Assembly

“…[ 42 ] In addition, since the helical phase is an intermediate state in chiral PLA‐containing BCs, it would evolve into equilibrium double‐gyroid phases after annealing for an extended period. [ 40,43 ] The hydrolysis of the PLA block resulted in the formation of a nanoporous PS matrix with gyroid nanochannels, which could function as removable templates to fabricate nanoporous gyroid structures composed of all types of elements and materials for different functions. These functions include, nanoporous gyroid Pt for electrochemical catalysis, nanoporous gyroid metallic oxides for optoelectronic applications, nanoporous epoxy for protein adsorption, and nanoporous Ni/NiO/C composites for electrical properties.…”

Controlling Self‐Assembly in Gyroid Terpolymer Films By Solvent Vapor Annealing

“…She et al demonstrated the controlled ordering of the double gyroid morphology in diblock copolymer thin films upon annealing in a neutral solvent and employing a functionalized substrate . Similarly, Wu et al explored the effect of swollen thickness and solvent removal rate on the resulting morphology of solvent‐annealed gyroid‐forming diblock copolymers . Both publications report, however, morphological transitions to the cylinder phase, despite the use of a supposedly neutral solvent.…”

Perpendicular Structure Formation of Block Copolymer Thin Films during Thermal Solvent Vapor Annealing: Solvent and Thickness Effects

“…However, SVA is a more complex process than thermal annealing. The morphology in this process not only depends on the intrinsic properties of BCP, such as the extent of χ , the degree of polymerization ( N ), and the composition (block ratio f ), but also on type of the solvent [12,13,14,15,16,17,18,19] and the film thickness [20,21,22]. Generally, preferentially wetting of one block at the substrate surface or free surface on the contrary induces preferential parallel orientation of domains [22].…”