Mixtures of solvents and mixtures of block copolymers as tools for tunable structures in block copolymer thin films
Final Report Abstract
Goal of the common project was the investigation of thin films from binary blends of diblock copolymers and of the solvent vapor annealing of diblock copolymer thin films using mixtures of solvent vapors. Theoretical work and computer simulations by the Russian partner were combined with experimental work of the German partner. The latter was largely based on experiments at large scale facilities. Diblock copolymer thin films from asymmetric diblock copolymers feature cylinders, whose orientation needs to be controlled for applications in sensors or nanolithography. Using computer simulations, we identified the conditions under which lying or standing cylinders form during solvent evaporation from an initially disordered swollen state. A vertical orientation of the cylinders is observed for a high evaporation rate, which leads to a pronounced gradient of the solvent concentration within the film. Also, a certain solvent selectivity for the longer matrix blocks is necessary. Thin films from binary blends of chemically equal, lamellae-forming diblock copolymers were investigated by combining computer simulations and GISAXS experiments. Depending on, among others, the film thickness and the selectivity of the surface, two types of macrophase separation were identified, namely lateral or vertical, i.e. along the film normal. The latter occurs mainly in thick films with the short copolymers accumulating near the film interfaces and the long ones populating the center of the film. For a substrate which is selective to one of types of blocks, the lamellae are parallel to the substrate surface, whereas they are perpendicular inside. Experiments on thin films from binary blends on lamellae-forming polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymers having different molar masses were investigated using grazing-incidence small-angle X-ray scattering (GISAXS). The films display lamellae having both, the parallel and the perpendicular orientation. The period of the lying lamellae in the one-phase state follows the theoretical prediction for the bulk. For a certain range of mixing ratios, the thin films are macrophase-separated. Moreover, thin films from binary blends of chemically equal, short lamellae-forming and long cylinder-forming diblock copolymers were investigated by computer simulations. It was found that a gyroid-like structure can be obtained for certain mixing ratios. For solvent vapor annealing with two independently prepared solvents and in situ, real-time GISAXS measurements of the structural changes, a setup was designed. We carried out experiments where diblock copolymer thin films were swollen in one solvent, which was gradually exchanged by another solvent, having a different selectivity. Moreover, temperature variation enabled us to control the time scales. Using this new setup, we carried out experiments on thin films from polystyrene-b-poly(dimethylsiloxane) (PS-b-PDMS) diblock copolymers featuring PDMS cylinders in a PS matrix. The films were first swollen in one of the solvents (n-heptane, which is selective for PDMS, or toluene, which is weakly selective for PS); after some time, this solvent was gradually exchanged by the other solvent. The morphologies in dependence on the overall solvent uptake and the vapor composition were determined using in situ GISAXS. Changes of both, the orientation of the cylinders and of the morphology to lamellae were identified. The related solvent partitioning and thus the overall solvent (or polymer) volume fraction and the effective volume fraction of the minority domain were calculated from the (measured) swelling ratio and the scattering contrast, i.e. the intensity of a chosen Bragg reflection. These experiments allow to identify the conditions needed to obtain a certain morphology and orientation in block copolymer thin films.
Publications
- Solvent vapor treatment of diblock copolymer thin films. An in-situ, real-time GISAXS investigation. ELETTRA Annual Report 2015
D. Posselt, A. V. Berezkin, F. Jung, H. Amenitsch, C. M. Papadakis
- In-situ x-ray scattering studies of solvent vapor annealing reviewed. CHESS Highlight, Dezember 2016
D.-M. Smilgies
- Vertical domain orientation in cylinderforming diblock copolymer films upon solvent vapor annealing. Macromolecules 49, 415-424 (2016)
A.V. Berezkin, C.M. Papadakis, I.I. Potemkin
(See online at https://doi.org/10.1021/acs.macromol.5b01771) - Restructuring in block copolymer thin films: In-situ GISAXS investigations during solvent vapor annealing. Progr. Polym. Sci. 66, 80-115 (2017)
D. Posselt, J. Zhang, D.-M. Smilgies, A. Berezkin, I. I. Potemkin, C.M. Papadakis
(See online at https://doi.org/10.1016/j.progpolymsci.2016.09.009) - Vertical or lateral – this is the question! CHESS Highlight, Mai 2017
C. M. Papadakis, D. Posselt, D. Smilgies
- Vertical vs lateral macrophase separation in thin films of block copolymer mixtures: Computer simulations and GISAXS experiments. ACS Appl. Mater. Interf. 9, 31291-31301 (2017)
A. V. Berezkin, F. Jung, D. Posselt, D.-M. Smilgies, C. M. Papadakis
(See online at https://doi.org/10.1021/acsami.6b16563) - In situ tracking of composition and morphology of a diblock copolymer film with GISAXS during exchange of solvent vapors at elevated temperatures. Adv. Funct. Mater. 1706226 (2018)
A. V. Berezkin, F. Jung, D. Posselt, D.-M. Smilgies, C. M. Papadakis
(See online at https://doi.org/10.1002/adfm.201706226)
