EXPLORING THERMAL TRANSPORT IN ORGANIC AND HYBRID MATERIALS
Thermal transport processes of organic and hybrid materials play an important role in thermal management, energy-related functionality, and performance. However, the thermal transport properties and mechanism of those complicated materials remain largely unexplored. This dissertation consists of two chapters studying organic and hybrid materials. The first chapter exams the thermal switching of thermoresponsive polymer Poly(N-isopropylacrylamide) (PNIPAM) by the light-induced transient thermal grating technique. Thermal switches are of great importance to thermal management in a wide variety of applications. However, traditional thermal switches suffer from being large and having slow transition rates. To overcome these limitations, we took advantage of abrupt second-order phase transitions in thermoresponsive polymer aqueous solutions to enable fast thermal switching. In the second chapter, I will share our discovery of the remarkably weak anisotropy in the thermal conductivity of two-dimensional hybrid perovskite butylammonium lead iodide crystals. Two-dimensional (2D) hybrid organic-inorganic perovskites consisting of alternating organic and inorganic layers are a new class of layered structures. They have attracted increasing interest for photovoltaic, optoelectronic, and thermoelectric applications, where knowing their thermal transport properties is critical. We carry out both experimental and computational studies on thermal transport properties of 2D butylammonium lead iodide crystals and find their thermal conductivity is ultralow (below 0.3 W m^(-1) 〖 K〗^(-1)) with very weak anisotropy (around 1.5) among layered crystals. Further analysis reveals that the unique structure with the preferential alignment of organic chains and complicated energy landscape leads to moderately smaller phonon lifetimes in the out-of-plane direction and comparable phonon group velocities in in-plane and out-of-plane directions. These new findings may guide the future design of novel organic and hybrid materials with desired thermal conductivity for various applications.
hybrid; organic; thermal transport
Benedek, Nicole A.; Xing, H. Grace
Ph. D., Mechanical Engineering
Doctor of Philosophy
dissertation or thesis