Effect of the Conformation Changes of Polyelectrolytes on Organic Thermoelectric Performances

Abstract

The relationship between the conformation of a polyelectrolyte and the performance of organic thermoelectric multilayers was studied. The conformational change of a weak polyelectrolyte via controlling assembling pH gave rise to a different thermoelectric behaviour in thin films. Organic thermoelectric multilayers were fabricated by alternately depositing bilayers (BL) of a positively-charged polyaniline (PANi) and multiwalled carbon nanotubes (MWNT), stabilized in poly(acrylic acid) (PAA), via a layer-by-layer assembly technique. The electrical conductivity and See-beck coefficient of PANi/MWNT-PAA nanocomposites were measured by varying assembly pH of PAA solutions. Altering the deposition pH of PAA resulted in different thermoelectric performances. A 40 BL thin film (∼210 nm thick) of PANi/MWNT-PAA assembled at pH 2.5/6.5 exhibited electrical conductivity of 95.2 S/cm and a Seebeck coefficient of 35 µV/K. This translates to a power factor of 11.7 µW/m·K2, which is 50 times higher than that of the same film with all components deposited at pH 2.5. Enhancement of thermoelectric behaviour in PANi/MWNT-PAA nanocomposites is attributed to a conjugated π-π network, together with a tightly packed nanostructure.