Dislocation-Mediated Lattice Curvature in Crystalline Polymers

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

Curvature deformations have been previously observed in thin films of optoelectronically active polymers and in single crystals showing uniform twist. However, the detailed manner in which three-dimensionally ordered polymer and molecular crystals are distorted by curvature remains to be clearly established. Direct imaging of the mechanisms of curvature will obtained using low dose high-resolution electron microscopy (HREM). Samples of organic molecular and polymer crystals with a variety of degrees of curvature will be prepared by depositing droplets onto solid surfaces, evaporating droplets in a column, electrospinning samples into nanometer diameters with oscillations in diameter, and by electric-field alignment of thin silicon nitride membranes. HREM images of the lattice spacings both parallel and perpendicular to the direction of curvature will be obtained and examined in detail. Theoretical considerations show that by examining the distance between partial dislocations that mediate curvature, and by measuring the characteristic distance between stacking faults, it is possible obtain estimates of the stacking fault energy on various crystallographic planes. These result will be compared with the predicted geometric distortions in the vicinity of the dislocation core as obtained by molecular modeling. %%% The results of this work will be useful in the design, synthesis, and processing of new organic materials with precisely controlled nanostructures. This research will facilitate the ongoing development of inexpensive, soft electronic devices. By elucidating the detailed means by lattice curvature is accommodated in synthetic molecular crystals, it should also be possible to learn how natural biological systems develop useful structures with similar symmetries.