Morphologies of diblock copolymer thin films before and after crystallization

G. Reiter; G. Castelein; P. Hoerner; G. Riess; J.-U. Sommer; G. Floudas

doi:doi:10.1007/s101890050014

2023 Impact factor 1.8

Soft Matter and Biological Physics

Eur. Phys. J. E 2, 319-334

Morphologies of diblock copolymer thin films before and after crystallization

G. Reiter¹ - G. Castelein¹ - P. Hoerner^1,2 - G. Riess^1,2 - J.-U. Sommer^1,3 - G. Floudas⁴

¹ Institut de Chimie des Surfaces et Interfaces - CNRS, 15, rue Jean Starcky, B.P. 2488, 68057 Mulhouse Cedex, France
² Ecole Nationale Supérieure de Chimie, 3 rue Alfred Werner, 68093 Mulhouse Cedex, France
³ Theoretische Polymerphysik, Universität Freiburg, Hermann-Herder Str. 3, 79104 Freiburg, Germany
⁴ Foundation for Research and Technology - Hellas (FORTH), Institute of Electronic Structure and Laser, P.O. Box 1527, 711 10 Heraklion Crete, Greece
g.reiter@univ-mulhouse.fr

Received 19 March 1999 and Received in final form 14 December 1999

Abstract
Spin-coated thin films of about 100nm of low-molecular-weight hydrogenated poly(butadiene-b- ethyleneoxide) ( $\ensuremath{\mathsf{PB_h}}$ -PEO) diblock copolymers have been crystallized at various constant temperatures. Crystallization has been observed in real time by light microscopy. Detailed structural information was obtained by atomic force microscopy, mainly enabled by the large viscoelastic contrast between amorphous and crystalline regions. The behavior in thin films is compared to the bulk properties of the polymer. Crystallization started from an annealed microphase separated melt where optical microscopy indicated a lamellar orientation parallel to the substrate. A small difference in the length of the crystallizable block produced significantly different crystallization behavior, both in the bulk and in thin films. For thin films of the shortest diblock copolymer (45% PEO content) and for an undercooling larger than about 10 degrees, crystallization created vertically oriented lamellae. These vertical lamellae could be preferentially aligned over several micrometers when crystallization occurred close to a three-phase contact line. Annealing at temperatures closer to the melting point or keeping the sample at room temperature for several months allowed the formation of a lamellar structure parallel to the substrate. A tentative interpretation based on kinetically caused chain folding and relaxation within the crystalline state, with implications on general aspects of polymer crystallization, is presented.