Kinetics of Domain Alignment in Block Polymer Thin Films during Solvent Vapor Annealing with Soft Shear: An in Situ Small-Angle Neutron Scattering Investigation

Abstract

We employed small-angle neutron scattering (SANS) to identify the kinetic pathways between disordered and ordered states in block polymer (BP) thin films subjected to solvent vapor annealing with soft shear (SVA-SS), which enabled the optimization of large-scale nanostructure ordering and alignment. The judicious incorporation of deuteration in poly­(deuterated styrene-b-isoprene-b-deuterated styrene) (dSIdS) films (≈200 nm thick) provided sufficient contrast in the SANS experiments to overcome the diffuse scattering contribution from thicker (nondeuterated) polydimethyl­siloxane (PDMS) pads (≈500 μm thick) and permit the in situ tracking of BP nanostructure responses to swelling, deswelling, and shear forces. We determined that as the dSIdS and PDMS swelled during SVA-SS, the lateral expansion of the PDMS across the pinned film induced a shear force that promoted chain mixing and nanostructure disordering in our solvent swollen systems. As solvent was removed from the films (deswelling), smaller grains began to form that had lower energetic barriers to alignment in the direction of the drying front(s), which facilitated nanostructure alignment. Changing SVA-SS parameters such as swelling ratio, PDMS elasticity, and deswell rate altered the ordering kinetics and affected domain directionality over a length scale that was readily captured through SANS studies. By exploiting SVA-SS parameters that create large and controllable shear forces, we also developed a robust and “hands-off” approach to direct BP thin film self-assembly using gradient thickness PDMS pads in SVA-SS. This proposed technique can be applied to quickly and reliably generate cost-effective microscopic patterns over macroscopic areas for both nanotechnology research and industrial applications.

Directional Self‐Assembly of Fluorinated Star Block Polymer Thin Films Using Mixed Solvent Vapor Annealing

“…and internal height = 1.75 in.). The vapor flowrate was tuned by two separate mass flow controllers (MKS Instruments Type 146C Cluster Gauge) as has been reported previously . For SVA, the BP film was annealed with propylene glycol methyl ether (PGME, Sigma‐Aldrich, used as received) vapor by bubbling nitrogen gas through a PGME reservoir to produce a solvent‐rich vapor stream with a flowrate of 30 mL min −1 .…”

“…The vapor flowrate was tuned by two separate mass flow controllers (MKS Instruments Type 146C Cluster Gauge) as has been reported previously. 69 For SVA, the BP film was annealed with propylene glycol methyl ether (PGME, Sigma-Aldrich, used as received) vapor by bubbling nitrogen gas through a PGME reservoir to produce a solvent-rich vapor stream with a flowrate of 30 mL min −1 . The film was annealed for 6 h to generate perpendicular-lamellae nanostructures; the film swelled tõ 2x its original thickness (from~50 nm to~100 nm) during this process.…”

“…The swelling and deswelling of a soft poly(dimethylsiloxane) (PDMS) pad generated a macroscopic shear stress that could directionally align BP thin film morphologies as the films were drying. This shear stress‐induced alignment by the soft PDMS pad has garnered substantial interest due to the high degree of achievable alignment and the relatively low fabrication costs associated with the process …”

“…This shear stress-induced alignment by the soft PDMS pad has garnered substantial interest due to the high degree of achievable alignment and the relatively low fabrication costs associated with the process. 43,63,68,69 Herein, we describe the directional alignment of fluorinated star BP thin films to achieve perpendicular-lamellae domains using a mixed solvent vapor feed. This mixed feed system was necessary to manage the disparate swelling behavior of the two polymer blocks, along with the swelling characteristics of the PDMS pad.…”

Defect Removal by Solvent Vapor Annealing in Thin Films of Lamellar Diblock Copolymers

“…In order to facilitate the fabrication of defect-free films, further treatments are needed. As examples to techniques that have been developed to tailor the self-assembly behavior of BCP thin films we mentioned electric field alignment 4,5 , shear alignment 6,7 , microwave annealing 8 , and thermal annealing 1,2,[9][10][11][12][13][14][15][16] . Besides these approaches, solvent vapor annealing (SVA) 1,3,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] has been used to enhance the mobility of polymer chains, and to facilitate the annihilation of defects.…”