‘Random walk’ of heat carriers in amorphous polymersThe intrinsic structure of a
‘Random walk’ of heat carriers in amorphous polymersThe intrinsic structure of amorphous polymers is highly disordered with long, entangled molecular chains. They are usually considered as thermal insulators due to their ultra-low thermal conductivity. One effective way to improve the thermal conductivity of amorphous polymers is modulating the chain conformation by external field, such as stretching force and electric field.Electrospinning serves as an effective way to control chain conformation. High electric voltage and stretching forces act on the jet during the fiber formation process. Therefore, the molecular chains tend to align along the fiber axis and be less entangled. It has been observed that thinner nanofibers tend to possess higher thermal conductivity, as Figure 1(a) shows. Nanofibers with a diameter larger than 150 nm possess thermal conductivity similar to bulk polymers, while the thermal conductivity of nanofibers with diameter smaller than 50 nm reaches an order of magnitude larger than that of bulk polyimide.One longstanding problem is how the chain conformation influences thermal conductivity. A recent study published in National Science Review distinguishes the heat transport within the chain and between different chains. Intra-chain heat transport should be more effective than inter-chain heat transport as the intra-chain covalent bond is stronger than inter-chain Van der Walls interactions. If the heat carriers undergo a random walk in the molecular chains, the thermal diffusivity corresponds to different chain conformations.Read more. -- source link
#materials science#science#amorphous#polymers#thermal conductivity#insulators#electrospinning#nanofibers#fibers#nanotechnology#heat flow