  The realization of phononic computing is held hostage by the lack of high
performance thermal devices. Here we show through theoretical analysis and
molecular dynamics simulations that unprecedented thermal rectification factors
(as large as 1.20) can be achieved utilizing the phase dependent thermal
conductivity of polyethylene nanofibers. More importantly, such high thermal
rectifications only need very small temperature differences (< 20 oC) across
the device, which is a significant advantage over other thermal diodes which
need temperature biases on the order of the operating temperature. Taking this
into consideration, we show that the dimensionless temperature-scaled
rectification factors of the polymer nanofiber diodes range from 12 to 25 -
much larger than other thermal diodes (< 8). The polymer nanofiber thermal
diode consists of a crystalline portion whose thermal conductivity is highly
phase-sensitive and a cross-linked portion which has a stable phase. Nanoscale
size effect can be utilized to tune the phase transition temperature of the
crystalline portion, enabling thermal diodes capable of operating at different
temperatures. This work will be instrumental to the design of high performance,
inexpensive and easily processible thermal devices, based on which thermal
circuits can be built to ultimately enable phononic computing.
