Thursday 14th of November 2013 at 16:00,  UCLan, MB051

Prof.Dr. Alexander Böker

Abstract

We elaborate on the time-evolution of electric field-induced reorientation of block copolymers and the distortion of lamellar domains. Due to a dielectric contrast between the two single components of diblock copolymers, phase separated microstructures orient with interfaces parallel to the electric field vector E. For symmetric poly(styrene-b-isoprene) diblock copolymers in toluene three mechanisms of reorientation are proposed, of which two, namely reorientation and nucleation & growth have been previously reported ^[1] Whereas the former is dominated by the rotation of entire grains, the latter is characterized by a disordering of unfavorably positioned domains, and subsequent growth of parallel lamellae. Here we present first experimental evidence of the third possible mechanism, selective disordering, in which lamellar grains parallel to E remain of equal size, whereas perpendicularly aligned structures disorder. By performing a sectorial evaluation of time-resolved scattering data recorded at the European Synchrotron Radiation Facility, ESRF (Grenoble, France), we were able to detect this orientation-dependent behavior with respect to disordering. Bragg peaks were evaluated with respect to the full width at half maximum, which displays itself as a function of the interaction parameter χ. This allowed determination of coherence lengths, i.e. grain sizes, within the polymer samples and how they evolve with time. The coherence lengths anisotropy inherent for differently oriented lamellar grains allows clear discrimination between the three mechanisms of orientation. We further performed a power-law analysis of the intensity-evolution with time for parallel and perpendicular domains, which suggests characteristic ratios and kinetics for each reorientation mechanism. ^[2]

References

[1] A. Böker, H. Elbs, H. Hänsel, A. Knoll, S. Ludwigs, H. Zettl, V. Urban, V. Abetz, A.H.E. Müller, G. Krausch “Microscopic Mechanisms of Electric-Field-Induced Alignment of Block Copolymer Microdomains” Phys. Rev. Lett. 2002, 89, 135502.

[2] M. Ruppel, C.W. Pester, K.M. Langner, G.J.A. Sevink, H.G. Schoberth, K. Schmidt, V.S. Urban, J.W. Mays, A. Böker “Electric Field Induced Selective Disordering in Lamellar Block Copolymers” ACS Nano, 2013, 7, 3854.