ChEMS Seminar: Directing Self-assembly in Nanostructured Soft Materials

Abstract: Self-assembly of block copolymers and small molecule mesogens gives rise to a rich phase behavior as a function of temperature, composition and other relevant parameters. The ability to precisely control their chemical functionality combined with the readily tunable characteristic length scales (~1-100 nm) of their self-assembled mesophases position these systems as a versatile and attractive class of materials for compelling applications ranging from membranes for size and chemo-selective transport, to lithography. As a result, there is intense interest in elucidating the physical processes relevant for directing self-assembly in these materials, with a goal of exploiting such fundamental understanding to create useful materials or devices. This presentation discusses recent advances in directed self-assembly of soft nanostructured materials and emerging methods for generating highly ordered and heterostructured systems. First, we consider the directed self-assembly of soft mesophases using magnetic fields, principally through the use of in situ X-ray scattering studies. Field alignment is predicated on a sufficiently large product of magnetic anisotropy and grain size to produce magnetostatic interactions which are substantial relative to thermal forces. We examine the role of field strength on the thermodynamics and alignment dynamics of a series of soft mesophases. The ability to produce highly ordered functional materials over macroscopic length scales is demonstrated, and we explore the role of alignment and connectivity in controlling anisotropic ionic transport in nanostructured systems. Recent exciting progress on low field (sub-1 T) alignment and the associated potential for orthogonal field imposition and local field screening are presented. Second, we examine electrospray deposition as a repurposed tool to generate well-ordered block copolymer thin films in a manner inspired by physical vapor deposition processes used in hard materials. The success of the method relies on slow deposition of sub-attoliter quantities of material delivered in sub-micron droplets produced by electrospray atomization. We demonstrate the ability to continuously deposit thin films with controlled orientation of microstructure, and to assemble heterostructures through sequential depositions of materials.

Bio: Osuji received his B.S. in materials science and engineering from Cornell University with a senior thesis on the use of random copolymers for polymer interface reinforcement supervised by Edward J. Kramer. He received his Ph.D. in materials science and engineering from MIT in 2003 for studies of structure-property relationships and self-assembly of liquid crystalline block copolymers, supervised by Edwin L. Thomas. After MIT he spent 2-1/2 years as a senior scientist at a startup company, Surface Logix Inc., where he conducted research on the use of soft lithography, microfluidics and surface patterning for fabricating cell-based assays, planar waveguides and other devices. Osuji conducted postdoctoral work on shear-induced structure formation and dynamics of colloidal gels with David A. Weitz in applied physics at Harvard from 2005-2007. In 2007, he joined the faculty at Yale University and is currently an associate professor in the Department of Chemical and Environmental Engineering. He leads an experimental research group focused on structure and dynamics of soft matter and complex fluids. Topics of interest include structure-property relationships in ordered soft materials, directed self-assembly of block copolymers and other soft mesophases, and rheology and slow dynamics of disordered systems. Osuji is the recipient of a CAREER award from the National Science Foundation (2008) and the 2010 Arthur Greer award of Yale College. He received an Office of Naval Research's Young Investigator award and a 3M Nontenured Faculty award in 2012. He is the 2015 recipient of the Dillon Medal of the American Physical Society and the 2015 Hendrick C. Van Ness Award.

Host: Ali Mohraz