Thermal Transport Phenomenon Of Suspended Quantum Dots and 2D Polymers

<p dir="ltr">Thermal transport in organic materials plays a decisive role in modern energy and electronic technologies, yet remains poorly understood because heat carriers depends on local chemistry, morphology, and interfaces. This thesis investigates how organics govern heat flow across two scales: at organic–inorganic interfaces and within extended crystalline lattices of two-dimensional polymers (2DPs). </p><p dir="ltr">In the first part of this work, I develop a numerical framework combining analytical solutions to the heat diffusion equation with finite element analysis to interpret pump–probe spectroscopy of nanocrystal suspensions. In these measurements, infrared excitation of surface ligands drives heat simultaneously into both the nanocrystal cores and the surrounding solvent. By fitting the experimental transients with my modeling framework, I am able to differentiate the nanocrystal/ligand and ligand/solvent interfacial conductances. The results show that the ligand/solvent boundary, with conductance of only 7–26 MW m^-2 K ^-1 , is the true bottleneck—an order of magnitude lower than the nanocrystal/ligand interface (88–135 MW m^-2 K ^-1 ). Beyond producing quantitative values, this work establishes a methodology for extracting interfacial conductances in complex, multiphase thermal systems. </p><p dir="ltr">The second part establishes the baseline thermal conductivity of 2DP thin films. Using frequency-domain thermoreflectance for cross-plane transport and suspended micro-platform calorimetry for in-plane transport, I discovered anisotropic thermal conductivity in imine-linked 2DPs, with (<i>k∥/k⊥</i>) up to 2.3. Thermal conductivity increases with temperature, consistent with grain-boundary-limited transport, while simulations of pristine crystals predict much larger values, highlighting the role of mesoscale disorder in limiting measured performance. These results provide the first experimental evidence of anisotropic thermal conductivity in 2DPs. </p><p dir="ltr">The final part of this thesis explores structural and chemical modifications to tune 2DP transport. Comparative measurements across frameworks with different linkers, pore sizes, and post-synthetic chemistries show that mesoscale order, grain size, orientation, and stacking, ultimately govern conductivity more strongly than idealized crystal structure. Chemical doping with NOBF4 modestly enhances cross-plane conductivity, while fullerene (C60) inclusion produces framework-dependent outcomes: substantial enhancement in one system, no change in another, and strong suppression in a third. These contrasting behaviors reflect a competition between lattice stiffening and added phonon scattering, underscoring both the opportunities and complexities of thermal property control in 2DPs. </p><p dir="ltr">Collectively, this thesis demonstrates that organic matter is not simply a passive thermal barrier, but a tunable medium whose transport properties emerge from the interplay of chemistry, structure, and mesoscale order. By establishing quantitative thermal conductances at nanocrystal interfaces, benchmarking anisotropic thermal transport in 2DPs, and revealing structure-dependent pathways to tune their thermal conductivity, this work provides a foundation for engineering organic and hybrid materials in thermal management.</p>