Decrease in thermal conductivity in polymeric P3HT nanowires by size-reduction induced by crystal orientation: New approaches towards thermal transport engineering of organic materials

To date, there is no experimental characterization of thermal conductivity of semiconductor polymeric individual nanowires embedded in a matrix. This work reports on scanning thermal microscopy measurements in a 3ω configuration to determine how the thermal conductivity of individual nanowires made of a model conjugated polymer (P3HT) is modified when decreasing their diameters. We observe a reduction of thermal conductivity, from λ_NW = 2.29 ± 0.15 W K^-1 m^-1 to λ_NW = 0.5 ± 0.24 W K^-1 m^-1, when the diameter of nanowires is reduced from 350 nm to 120 nm, which correlates with the polymer crystal orientation measured by WAXS. Through this work, the foundations for future polymer thermal transport engineering are presented.