The theories of thermal transport in polymers, which are mainly qualitative, are reviewed. The behaviour of amorphous polymers is better understood than that of partially crystalline ones. An apparatus for measuring the thermal conductivity of solid and molten polymers from room temperature to 250 degrees C is described. 'Edge effects' are eliminated by enclosing the heat source and samples inside the heat sink; hence guard rings are not used. The heat flow is three dimensional and the conductivity is obtained by a numerical calculation. Two disc shaped samples 48mm diameter and 2mm thick are required. An apparatus for measuring the thermal diffusivity of solid and molten polymers from room temperature to 250 degrees C is also described. Disc samples the same size as for the conductivity apparatus are used and the heat equation is again solved numerically. Conductivity and diffusivity results are reported for high density polyethylene, polypropylene, three grades of polymethyl methacrylate, three grades of polystyrene, and a series of carbon black filled natural rubber compounds. To show the effect of molecular weight, conductivity results for a range of polyethylene glycols and a range of silicone fluids are also presented.

Understanding thermal transport processes can guide the rational design of devices and systems for thermal energy conversion and management. Despite the significant progress in thermal transport of inorganic crystals, thermal transport in complicated materials, such as polymers and hybrid materials, remains largely unexplored. This thesis first presents our discovery of the large thermal rectification effects in the novel tapered bottlebrush polymers using nonequilibrium molecular dynamic simulations. In sharp contrast to all other reported asymmetric nanostructures, we observed that the heat current from the wide end to the narrow end in tapered bottlebrush polymers is smaller than that in the opposite direction. It was demonstrated that a more disordered to less disordered structural transition within tapered bottlebrush polymers is essential for generating non-linearity in heat conduction for thermal rectification. Moreover, the thermal rectification factor increases with device length, reaching as high as ~70% with a device length of 28.5nm. This large thermal rectification with strong length dependence uncovers an unprecedented phenomenon - diffusive thermal transport in the forward direction and ballistic thermal transport in the backward direction. This thesis then focuses on thermal transport properties in hybrid materials: graphene-C60 heterostructures and hybrid organic-inorganic (CH3NH3)3Bi2I9 crystals. Graphene-C60 heterostructures assembled by van der Waals interactions between graphene and C60 have shown exciting potential for multifunctional devices. Understanding thermal transport in graphene-C60 heterostructures is the key to guiding the design of vdW heterostructures with desired thermal transport properties. Our equilibrium molecular dynamics simulations found that the in-plane thermal conductivity of the graphene-C60 heterostructure is as high as about 234 W/(mK) at room temperature, exceeding those of most pure metals. On the other hand, vdW interactions enhance the interfacial thermal conductance between graphene and C60 by strengthening out-of-plane phonon couplings between graphene and C60 and increasing in-plane and out-of-plane phonon couplings of the graphene layer. Our study demonstrates that the interfacial thermal conductance of graphene-C60 heterostructure is comparable to that of graphene-hexagonal boron-nitride (hBN) heterostructure. Hybrid perovskite analogues, such as methylammonium bismuth iodide (CH3NH3)3Bi2I9, have emerged as candidate photovoltaic and thermoelectric materials due to their low toxicity and high stability. Thermal transport and phonon properties of (CH3NH3)3Bi2I9 were studied neither experimentally nor theoretically, which hinders the optimal selection and design of stable, non-toxic hybrid perovskite material for photovoltaic and thermoelectric applications. We mapped out the phonon dispersion of (CH3NH3)3Bi2I9 single crystals at 300 K using inelastic x-ray scattering. The frequencies of acoustic phonons are among the lowest of crystals. Nanoindentation measurements verified that these crystals are very compliant and considerably soft. The frequency overlap between acoustic and optical phonons results in strong acoustic-optical scattering. All these features lead to an ultralow thermal conductivity.

Transport Properties of Polymeric Membranes is an edited collection of papers that covers, in depth, many of the recent technical research accomplishments in transport characteristics through polymers and their applications. Using the transport through polymer membranes method leads to high separation efficiency, low running costs, and simple operating procedures compared to conventional separation methods. This book provides grounding in fundamentals and applications to give you all the information you need on using this method. This book discusses the different types of polymer, their blends, composites, nanocomposites and their applications in the field of liquid, gas and vapor transport. Some topics of note include modern trends and applications of polymer nanocomposites in solvent, vapor and gas transport; fundamentals and measurement techniques for gas and vapor transport in polymers; and transport properties of hydrogels. This handpicked selection of topics, and the combined expertise of contributors from global industry, academia, government and private research organizations, make this book an outstanding reference for anyone involved in the field of polymer membranes. - Presents current trends in the field of transport of liquid, gas and vapor through various polymeric systems - Features case studies focused on industrial applications of membrane technology, along with fundamentals of transport and materials - Helps readers quickly look up a particular technique to learn key points, capabilities and drawbacks

The broad objective of the work was to relate charge, heat, and mass transport in the Air Force's extended chain polymers (especially poly-para-phenylene benzobisthiazole PBT) to other electrical, thermal, mechanical nad microstructural properties of the polymers and also to compare these very unusual, highly anisotropic Air Force materials with other materials when it is scientifically relevant or when potential applications may be involved. Special techniques were developed for making transport-property determinations on samples in the form of thin fibers and small area films. Two types of miniature cells were developed in the study of PBT transport properties. A very promising area of the research relates to an anisotropic version of the Barker-Sharbaugh weak electrolyte model for ionic conduction in polymers. A new technique which has been termed the diffusion controlled-differential current (DCDC) method evolved from experiments related to the weak electrolyte model. This DCDC-technique looks promising as a new analytical tool. The results for PBT turned out to be especially interesting because the ratio of ionic conductivities parallel and perpendicular to the chain axis was very large (100,000 at 300 K) and temperature dependent (smaller ratio at a higher temperature). Special techniques for the thermal conductivity allowed the axial and perpendicular thermal conductivities to be determined.