The attractiveness of polymers generally stems from their lightweight, low cost, and offer freedom-of-design using large-scale manufacturing techniques. Their corrosion resistance, low dielectric constants among other attributes are appealing properties for specific applications such as heat exchangers for corrosive environments and heat sinks in compact electronic devices. However, polymers are considered thermal insulators, therefore these applications have been, primarily restricted to metals and their alloys. Nonetheless, our fundamental understanding of thermal transport in polymeric systems needs to be drastically improved to gain the capability to design systems for thermal applications from the outset. The abundance of variety of polymers systems renders this task highly challenging. Here, we use polymers with model functional groups such as poly(vinyl alcohol) (PVAL) to discuss the various effects of solid-state structure on overall thermal transport. Blending with an oligomer was shown to influence the local chain order via hydrogen bonding, and in turn, influencing the thermal conductivity. It was revealed that at low concentrations (5-15 wt.% of the oligomer), a localised extension of the PVAL backbone bonds occurred. However, with higher oligomer concentrations, the main change observed was a plasticising effect.
Organic/inorganic hybrid systems were studied next. They are an attractive new field of research as they offer tunability of a range of properties, yet the effects on thermal conductivity were yet to be investigated. The hybrid system based on PVAL / titanium oxide hydrate was revealed to have favourable thermal transport network despite having a lesser ordered molecular structure. This system was compared to a conventional PVAL – TiO2 composite to draw contrasts with the formed structures.
Finally, a novel preparation of PVAL with Aramid nanofibers (ANF) films was studied and the effect on thermal conductivity was explored. A more intimate interaction between the ANF and PVAL chains compared to methods reported in literature was revealed using various vibrational and electron spectroscopy techniques. The effects on the thermal conductivity were more significant compared to the hybrid and blend systems. Overall similarities can be drawn between the three multicomponent systems, which allows us to establish design rules and broadly applicable structure-thermal conductivity relationships. Ultimately, we provided a general understanding on a broad range of systems that can be used to tune the thermal conductivity of macromolecules to the final required properties.