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.
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