Tracking Solvent Distribution in Block Polymer Thin Films during Solvent Vapor Annealing with in Situ Neutron Scattering

Abstract

Herein, we employed in situ small-angle neutron scattering (SANS) and neutron reflectivity (NR) to elucidate the importance of polymer–solvent interactions on morphology development during solvent vapor annealing (SVA) of block polymer (BP) thin films. Judicious choice of nanostructure orientation (parallel to the substrate) permitted measurement of the preferential segregation of solvent (d 6-benzene) into our cylinder-forming poly­(styrene-b-isoprene-b-styrene) (SIS) films. A distinguishing feature of this work is the simultaneous tracking of nanostructure evolution and solvent segregation, enabled through the combination of SANS (in-plane features), NR (out-of-plane features), and solvent deuteration, which directly related polymer–solvent interactions to morphology reorganization. We found that at higher d 6-benzene partial pressures (p/p sat) the number of cylinder layers (domains) increased or decreased to accommodate overall film thickness changes upon swelling/deswelling, while the SIS domain spacing remained nearly constant. However, at lower p/p sat values, the SIS domain spacing changed to accommodate similar swelling/deswelling variations, while the number of layers remained invariant. The threshold for this p/p sat transition was directly related to plasticization of the polystyrene (PS) block, which has significant implications on the size of the domains, degree of ordering, and interfacial roughness. Thus, by linking polymer–solvent interactions to morphology evolution, we have developed an improved understanding of the interplay between the kinetic and thermodynamic effects that can direct the self-assembly and through-film periodicity of nanostructured thin films.

In Situ Tracking of Composition and Morphology of a Diblock Copolymer Film with GISAXS during Exchange of Solvent Vapors at Elevated Temperatures

“…Whereas the film thickness can be monitored readily using spectroscopic reflectometry and may be transformed into an overall solvent volume fraction in the film (or, equivalently, the polymer volume fraction, φ P ), the detailed distribution of the two solvents is not easily accessible. A recent work demonstrates that the distribution of a deuterated solvent in a nondeuterated BCP may be determined by in situ small‐angle neutron scattering (SANS) and in situ neutron reflectometry . While the significant neutron scattering contrast of deuterated and nondeuterated components is of great advantage, deuterated components (such as partially deuterated BCPs) are not always accessible.…”

“…While the significant neutron scattering contrast of deuterated and nondeuterated components is of great advantage, deuterated components (such as partially deuterated BCPs) are not always accessible. Moreover, large sample volumes and long measuring times (2 h were reported for the SANS experiments) are needed for these techniques, which may hamper an efficient screening of the parameter space, and lateral and vertical information are only obtained separately. For solvent vapor mixtures, as used in the present work, combinatorial experiments with deuterated and nondeuterated solvents or even with partially deuterated BCPs would be required.…”

Tuning Block Polymer Structure, Properties, and Processability for the Design of Efficient Nanostructured Materials Systems

“…Recently, the Epps group has designed and fabricated experimental SVA configurations that enable in situ neutron scattering during annealing to track solvent distribution and nanoscale structural changes in BP films during treatment . Neutron scattering is particularly suited to SVA studies because sufficient contrast between solvent and both polymer blocks can be easily achieved through deuteration, which facilitates a detailed mapping of solvent segregation throughout the film .…”

“…At low solvent content (effective T g of PS above 25 °C), the chain mobility was constrained, causing the number of layers to stay constant while the vertical domain spacing decreased. Adapted with permission . Copyright 2016, American Chemical Society.…”

Synergic Swelling of Interactive Network Support and Block Copolymer Films during Solvent Vapor Annealing

“…We note that the values of p/p 0 evaluated in this study are higher than the actual vapor pressure in the chamber because of the flow conditions. An exact way is to measure the partial pressure of solvent at each ratio using, for example, mass spectrometry at the chamber outlet, as was properly performed by Shelton et al 64 The stability of the processing conditions was monitored via measurements of the swollen films thickness h sw . The polymer volume fraction in a swollen film is estimated as: ϕ = h dr /h sw , where h dr is the thickness of the as-spin-coated and dried films.…”