In situ GISAXS study of a Si-containing block copolymer under solvent vapor annealing: Effects of molecular weight and solvent vapor composition

Abstract

The room-temperature solvent vapor annealing of polystyrene-b-polydimethylsiloxane (PS-b-PDMS) block copolymer films was studied in situ by grazing incidence small-angle X-ray scattering. Films of cylinder-forming PS-b-PDMS with molecular weight 16 kg/mol and 12.2 kg/mol, annealed under vapors of toluene: heptane with varying composition, exhibited swelling-ratio-dependent evolution of microdomain spacing and orientation. In a vapor made from a toluene: heptane 5:1 volumetric ratio liquid mixture, or from pure toluene, cylindrical microdomains reoriented from majority out-of-plane to in-plane during annealing, while drying led to shrinkage along the film normal and a large distortion of the hexagonal lattice of in-plane cylinders. Annealing under vapor from a toluene: heptane 1:5 volumetric ratio liquid produced a non-bulk lamellar structure in the 16 kg/mol PS-b-PDMS.

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

“…These observations point to a slight reorganization of the cylindrical structure. We attribute the reorientation toward the vertical orientation to the rapid vertical transfer of the solvent into the film, resulting in a solvent concentration gradient . The difference in viscosities of the cylinders and the matrix and interfacial flows may also play a role …”

“…We note that the transition to the lamellar morphology and back to the cylindrical morphology upon the stepwise exchange of n ‐heptane by toluene is consistent with the observations in ref. , where few solvent vapor compositions were studied.…”

“…The technique is especially efficient in case of two solvents with well‐known and notably different selectivities toward different nanodomains. Using a mixture of a weakly and a strongly selective solvent allows to induce a morphology change from the cylindrical to the lamellar morphology, in consistency with previous studies, and to control the orientation of the nanodomains. In contrast to posttreatment, ex situ investigations based on imaging, the in situ resolved GISAXS experiments presented in this paper are far more efficient, less prone to artifacts due to sample preparation, and more suitable to thicker films.…”

“…Solvent vapor annealing (SVA) is a widely used method to obtain highly ordered nanostructured BCP thin films, which also has been applied to modify the BCP thin film morphology . In recent years, the efficiency of this approach was improved by the so‐called warm or solvothermal vapor annealing (STVA) .…”

Synchrotron Radiation for the Understanding of Block Copolymer Self-assembly

“…The characterization of thin films using GISAXS is also compatible with standard self-assembly condition (thermal or solvent annealing) that, together with the highly time-resolved data acquisition, makes this technique ideal for in-situ and real-time characterization of self-assembly process. However, the majority of the studies using GISAXS on block copolymer thin films have been performed in static mode on previously selfassembled layers and most of the studies of in-situ real-time block copolymer evolution are mainly related to solvent annealing process [18,19] In this paper, we present the in-situ and real time characterization of the self-assembly process of a lamellar PS-b-PMMA Poly[styrene-block-(methyl methacrylate)]. The block copolymer will be annealed under isothermal conditions and the parameters of the block copolymer kinetics will be extracted from 2D-GISAXS patterns taken during the annealing process.…”