Influence of Initial Order on the Microscopic Mechanism of Electric Field Induced Alignment of Block Copolymer Microdomains Kristin Schmidt, † Alexander Bo ¨ker,* ,†,‡ Heiko Zettl, † Frank Schubert, † Helmut Ha ¨ nsel, † Franz Fischer, § Thomas M. Weiss, ⊥ Volker Abetz, | A. V. Zvelindovsky,* ,#,¶ G. J. A. Sevink, x and Georg Krausch* ,†,O Lehrstuhl fu ¨ r Physikalische Chemie II, Universita ¨ t Bayreuth, D-95440 Bayreuth, Germany, Lehrstuhl fu ¨ r Kristallographie, Universita ¨ t Bayreuth, D-95440 Bayreuth, Germany, European Synchrotron Radiation Facility (ESRF), F-38043 Grenoble, France, GKSS-Forschungszentrum Geesthacht GmbH, Institut fu ¨ r Polymerforschung, Max-Planck-Strasse, D-21502 Geesthacht, Germany, Centre for Materials Science, Department of Physics, Astronomy & Mathematics, University of Central Lancashire, Preston PR1 2HE, United Kingdom, and Leiden Institute of Chemistry, Universiteit Leiden, P.O. Box 9502, 2300 RA Leiden, The Netherlands Received May 20, 2005. In Final Form: July 7, 2005 We investigate the mechanism of microdomain orientation in concentrated block copolymer solutions exposed to a dc electric field by in situ synchrotron small-angle X-ray scattering (SAXS). As a model system, we use concentrated solutions of a lamellar polystyrene-b-polyisoprene block copolymer in toluene. We find that both the microscopic mechanism of reorientation and the kinetics of the process strongly depend on the initial degree of order in the system. In a highly ordered lamellar system with the lamellae being aligned perpendicular to the electric field vector, only nucleation and growth of domains is possible as a pathway to reorientation and the process proceeds rather slowly. In less ordered samples, grain rotation becomes possible as an alternative pathway, and the process proceeds considerably faster. The interpretation of our finding is strongly corroborated by dynamic self-consistent field simulations. Introduction Supramolecular self-assembly has recently become an area of increasing interest particularly due to its potential for large scale creation of nanostructured materials. Block copolymers are a prominent class of such materials as they spontaneously form ordered mesostructures of dif- ferent symmetry (lamellae, hexagonally packed cylinders, and cubic lattices of spheres) with characteristic length scales in the 10-100 nm regime. In view of potential applications, however, the control of long-range orienta- tional order and the removal of defects remains a crucial issue. Here, the manipulation or guidance of the spon- taneous processes by application of controlled external fields (e.g., mechanic, electric, magnetic) proves to be a promising approach. Rather straightforward, macroscopic experiments (shear cells, capacitors, magnets) have proven successful to create long range order in the block copolymer nanostructures. 1-5 Owing to the different dielectric properties of the two blocks, an orientation of block copolymer microdomains parallel to an external electric field is energetically favored. The orientation of block copolymer microdomains by means of an electric field has been shown to be feasible with field strengths ranging from one to several tens of volts per micrometer, depending on the difference between the dielectric constants. Recent experiments and computer simulations have shown that two distinctly different microscopic pathways are possible when an ordered block copolymer mesostructure of arbitrary orientation is ex- posed to an external electric field. 6-8 In the case of sufficiently weak segregation between the two blocks, local nuclei of the favored parallel orientation are created. Subsequently, these nuclei grow. Consequently, in a scattering experiment, only the initial and the final orientations are observed with the intensity of the latter growing on expense of the former. Alternatively, in the case of stronger segregation between the respective blocks, the orientation of entire grains rotates, mediated by movement of individual defects perpendicular to the microdomain structure, until the favored orientation parallel to the field is reached. In this case, a scattering experiment will detect a continuous shift of the scattering pattern from the initial to the final orientation as has * Corresponding authors. † Lehrstuhl fu ¨ r Physikalische Chemie II, Universita ¨ t Bayreuth. ‡ E-mail: alexander.boeker@uni-bayreuth.de. § Lehrstuhl fu ¨ r Kristallographie, Universita ¨ t Bayreuth. ⊥ European Synchrotron Radiation Facility (ESRF). | GKSS-Forschungszentrum GmbH. # University of Central Lancashire. x Universiteit Leiden. O E-mail: georg.krausch@uni-bayreuth.de. ¶ E-mail: avzvelindovsky@uclan.ac.uk. (1) Thurn-Albrecht, T.; DeRouchey, J.; Russell, T. P.; Jaeger, H. M. Macromolecules 2000, 33, 3250-3253. (2) Amundson, K.; Helfand, E.; Davis, D. D.; Quan, X.; Patel, S. S.; Smith, S. D. Macromolecules 1991, 24, 6546-6548. (3) Bo ¨ ker, A.; Knoll, A.; Elbs, H.; Abetz, V.; Mu ¨ ller, A. H. E.; Krausch, G. Macromolecules 2002, 35, 1319-1325. (4) Ebert, F.; Thurn-Albrecht, T. Macromolecules 2003, 36, 8685- 8694. (5) Keller, A.; Pedemonte, E.; Willmouth, F. M. Nature (London) 1970, 225, 538-539. (6) Bo ¨ker, A.; Elbs, H.; Ha ¨ nsel, H.; Knoll, A.; Ludwigs, S.; Zettl, H.; Zvelindovsky, A. V.; Sevink, G. J. A.; Urban, V.; Abetz, V.; Mu ¨ ller, A. H. E.; Krausch, G. Macromolecules 2003, 36, 8078-8087. (7) Bo ¨ker, A.; Elbs, H.; Ha ¨ nsel, H.; Knoll, A.; Ludwigs, S.; Zettl, H.; Urban, V.; Abetz, V.; Mu ¨ ller, A. H. E.; Krausch, G. Phys. Rev. Lett. 2002, 89, 135502. (8) Zvelindovsky, A. V.; Sevink, G. J. A. Phys. Rev. Lett. 2003, 90, 049601. 11974 Langmuir 2005, 21, 11974-11980 10.1021/la051346w CCC: $30.25 © 2005 American Chemical Society Published on Web 08/23/2005