Investigation of liquid sensing mechanism of poly(lactic acid)/multi-walled carbonnanotube composite films

Abstract

The liquid sensing mechanism of melt-processed poly(lactic acid) (PLA)/multi-walledcarbon nanotube (MWNT) composite films was investigated for the influence of MWNTloading, solubility parameters of solvents used, solvent transport behaviours, resultantelectrical resistance changes, as well as crystallization of the PLA matrix. Thediffusion, sorption and permeation coefficients of neat PLA and the composites wereestimated, indicating that MWNT network structures block solvent moleculesfrom penetrating into the polymer matrix. Solvent-induced crystallization of thepolymer matrix was observed. Isothermally crystallized composites showed reducedresistances, a significant decrease of sorbed solvent content and a reduction of theresulting resistance changes on the solvent contact. In the context with sensingresults on MWNT mats, it was proposed that the liquid sensing mechanism ofPLA/MWNT composites consists of the overall electrical resistance changes causedby the structural variation of the conductive MWNT network in the polymermatrix and additional interactions between the MWNT and solvent molecules.