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Kinetics of Domain Alignment in Block Polymer Thin Films during Solvent Vapor Annealing with Soft Shear: An in Situ Small-Angle Neutron Scattering Investigation
journal contribution
posted on 2017-07-10, 18:06 authored by Cameron
K. Shelton, Ronald L. Jones, Thomas H. EppsWe
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.