Grace Han, PhD

Grace HanAssistant Professor
Department of Chemistry
Brandeis University
October 1, 2018

Responsive Shape-Changing Molecules for Energy Storage and Conversion

Phase-change materials release heat when they go through a change in physical state (such as solid to liquid). This heat, or thermal energy, has a variety of uses, including thermal batteries. However, it can be difficult to modulate storage times and temperatures for this energy source. Dr. Han discussed the work of her group on extending the length of time heat could be stored, and at what temperature, to improve thermal batteries.

Traditional phase-change materials (PCMs), both inorganic and organic, with high latent heat densities are valuable means for harnessing waste heat from industrial processes and solar irradiation. However, the active control of thermal energy storage and release remains a challenge, as a result of the spontaneous dissipation of heat to cooler surroundings. In the Han group, we develop optical methods that enable active manipulation of thermodynamic parameters of conventional PCMs, as a complementary tool to passive thermal insulation which controls the kinetics of thermal energy dissipation. Organic photo-switching elements have perfect efficacy as dopants, interfacial functional groups, and polymer functional groups to regulate the nucleation dynamics of PCMs. The new functional modalities will extend thermal energy storage times and the range of storage temperatures for deployable thermal batteries.

We are also developing a new method that allows us to directly image the fundamental photoswitching behavior of molecules. Annular dark-field scanning transmission electron microscopy (ADF-STEM) and a highly electron-beam transparent graphene support are used to track molecular structure changes of photoswitches. Platinum atom markers attached to photoswitching organic molecules show effective length change from ~2.1 nm to ~1.4 nm upon UV irradiation, indicative of a trans-to-cis isomerization. This approach taking advantage of individual isolated heavy metal atoms as markers into complex molecules provides an effective method to study a diverse range of complex organic materials at the single molecule level.