3D Imaging of Defects in Soft-Matter Crystals

ABSTRACT

Many block copolymers form soft crystals with unit cells typically about 1000x larger than the unit cells of most metals and ceramics. Nevertheless, many of the same point, line, and planar defects found in hard matter appear in soft matter. By using an ion beam to mill thin slabs (3 nm thickness) from a many micron2 area (‘slice’) and capturing low voltage (~ 1 keV) scanning electron images (‘view’), large volume slice-and-view scanning electron microscopy 3D tomograms can be constructed by registering the stack of images. These 3D tomograms provide compelling images of the rich morphologies that can be generated by block copolymer microphase separation. Software slicing of the 3D tomogram allows extraction of the core region associated with a defect. Moreover, detailed structural characterization affords measurement of microdomain shapes and sizes as well as the distribution of curvatures over the intermaterial dividing surface (IMDS) that separates one microphase (e.g., polystyrene) from another microphase (e.g., polyisoprene). Comparison to a nearby defect-free region allows assessment of the deformation and transformation of the IMDS due to the presence of the defect. 3D FFT of selected volumes enables measurement of the local unit cell parameters including quantification of distortions in lengths and angles due to defects. The presence of a planar defect, for example, can introduce new types of packing and alters the local network geometry and topology. The adaptation of the structure near the defects emphasizes the remarkable malleability of soft matter.

BIOGRAPHY

Edwin L. (Ned) Thomas is a materials scientist and engineer whose research spans polymer materials physics and engineering; photonic and phononic crystals; metamaterials, microtrusses, and 3D interference lithography; the ballistic and shock behavior of lightweight nanocomposites; and the optical and acoustic properties of soft matter systems. His work also advances materials characterization through electron microscopy and synchrotron X ray diffraction.

Ned previously served as Head of the Department of Materials Science and Engineering at the Massachusetts Institute of Technology (MIT) and was the founder and former director of the MIT Institute for Soldier Nanotechnology. He then served as the William and Stephanie Sick Dean of the George R. Brown School of Engineering at Rice University before joining Texas A&M University and most recently the University of Virginia. His honors include election to the National Academy of Engineering and the American Academy of Arts and Sciences, along with fellowships in the Materials Research Society, AAAS, and the American Physical Society. He is the author of The Structure of Materials, has co-authored more than 500 publications, and holds 22 patents.

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