2014: Morphology-Controlled Kinetics of Solvent Uptake by Block Copolymer Films in Nonselective Solvent Vapors

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The group of Prof. Dr. Igor I. Potemkn: Dr. Andrey A. Rudov and PhD-student Rustam A. Gumerov from the Chair of Polymer and Crystal Physics in collaboration with German colleagues from the DWI – Leibniz Institute for Interactive Materials, Aachen have detected and explained for the first time that solvent uptake by nanostructured block copolymer films in nonselective solvent vapors depends on the morphology of the film.

Block copolymers are macromolecules consisting of polymer chains (blocks) of different chemical structure covalently linked with each other. In many cases the blocks are incompatible with each other. As a result, they segregate at the length scales of macromolecular size and form nanodomains whose shape is primarily controlled by relative lengths of the blocks. This effect is known as microphase segregation. Nanostructured films on the basis of block copolymers are widely used in many applications including efficient matrixes for organic solar cells, ferromagnetic arrays of ultrahigh density for data storage, membrane technologies, etc. The key factors, which make the films very attractive, are the spatial symmetry of the nanodomains and huge interfacial area. The most simple and widely used way of preparation of the films - spin-coating - does not provide equilibrium structure of the nanodomains. In many cases the system is approached to the equilibrium state via solvent vapor annealing: the film is subjected to a cyclic procedure of swelling in solvent vapors with subsequent slow drying. Up to now, it was believed that non-selective solvents (the solvents have equal affinities to the blocks) must have equal effect on the block copolymer films independently on their internal structure. However, our studies have demonstrated that the solvent penetration inside the film proceeds mainly through the interfaces (see Figure) and kinetics of the solvent uptake depends on the nanodomain structure. The difference in the swelling rates can be on the order of magnitude. The obtained fundamental results can be very useful for many applications such as sensors on chemicals in atmosphere, supercapacitors, etc.

These results have been published (and featured at the cover of the journal) in the following paper: A. Stenbock-Fermor, A.A. Rudov, R.A. Gumerov, L.A. Tsarkova, A. Böker, M. Möller and I.I. Potemkin, “Morphology-Controlled Kinetics of Solvent Uptake by Block Copolymer Films in Nonselective Solvent Vapors”, ACS Macro Letters 3, 803-807 (2014).