In addition to its annual lectures, ChBE hosts a weekly seminar throughout the year with invited lecturers who are prominent in their fields. Unless otherwise noted, all seminars are held on Wednesdays in the Molecular Science and Engineering Building ("M" Building) in G011 (Cherry Logan Emerson Lecture Theater) at 4:00 p.m. Refreshments are served at 3:30 p.m. in the Emerson-Lewis Reception Salon.

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From molecules to devices, by controlling crystallization at interfaces

Molecular assembly processes, such as crystallization, aggregation, micro-phase separation etc, have a profound impact on the solid-state properties of materials. For instances, difference in crystal packing (polymorphism) influences bioavailability and stability of pharmaceutical compounds; morphology and molecular packing of organic semiconductors are critical to determining their charge transport characteristics; controlling the micro-phase separation is key to achieving high-efficiency organic solar cells. However, in all these areas, the level of control on molecular assembly attained in current solution processing methods fall far short of industrial requirements. This situation is due, in no small part, to the lack of fundamental understanding at molecular level.

In this talk, I will discuss strategies to control crystallization by designing interfaces, from their nanotopology, microstructure to surface chemistry. In the first example, I will present a study towards gaining fundamental understanding of heterogeneous nucleation, in the context of pharmaceutical manufacturing. Using nanostructured polymer substrates, I demonstrated contrary to the common belief that the shape of surface nanopores (10-100 nm), and the size of nanoscale confinement (0.7-2nm) are essential in determining the nucleation behavior. In the second example, I will discuss how the understanding of crystallization processes can be applied to solution printing of organic electronic devices. For the first time, I introduce the concept of flow engineering for controlling the thin film morphology of printed electronics (FLUENCE: fluid-enhanced crystal engineering). Herein, the flow engineering is achieved by designing the microstructure of the printing blade and the chemical patterns of the substrate. Enabled by this approach, highly-aligned single-crystalline organic thin-film transistors were fabricated, yielding unprecedented charge carrier mobility for the material studied. These examples show that the understanding and control of crystallization, and broadly speaking, molecular assembly processes, are key to manufacturing of next generation functional materials and devices in a wide range of areas, from energy, electronics, to healthcare.