Biomimetic Approach to Facilitate the High Filler Content in Free-Standing and Flexible Thermoelectric Polymer Composite Films Based on PVDF and Ag2Se Nanowires

Abstract

A high filler content is often needed in polymer composite-based thermoelectric (TE) films to improve their performance. Nevertheless, this often leads to poor processability and poor mechanical performance. Herein, a biomimetic approach is adopted to facilitate the filler content up to 90.5 wt % in free-standing and flexible n-type PVDF/Ag2Se TE films, where PVDF dendricolloids are a solution mixed with Ag2Se nanowires (NWs), followed by filtration. These soft dendric nanoparticles within PVDF dendricolloids have high adhesivity and strong network-building ability, which allows the formation of "grapevine-grape"-like networks with soft dendritic particles and inorganic TE fillers as "grapevine" and "manicure finger grapes", respectively. The maximum power factor of 189.02 μW m-1 K-2 is achieved for a PVDF/Ag2Se mass ratio of 1:9.5 at 300 K. Meanwhile, excellent flexibility with only 15.8% decrease in electrical conductivity after 1000 bending cycles was observed. These properties at such a high filler content are attributed to the long-range grapevine-like network of soft PVDF dendritic particles and entanglement between numerous Ag2Se NWs. This work carves a path to fabricate high-performance free-standing flexible n-type TE composite films as well as other functional polymer composites requiring high inorganic filler loading.