Noncovalent Functionalization of Multiwalled Carbon Nanotube by a Polythiophene-Based Compatibilizer: Reinforcement and Conductivity Improvement in Poly(vinylidene fluoride) Films

Abstract

A new compatibilizer (P2) containing thiophene moiety and poly(dimethylamino ethyl methacrylate) (PDMAEMA) group is prepared by atom transfer radical polymerization (ATRP). The dispersion of multiwalled carbon nanotube (MWNT) with P2 in N,N-dimethylformamide (DMF) is stable for >3 months. The UV–vis spectrum of the MWNT/P2 dispersion shows a blue shift, and the photoluminescence (PL) spectrum also indicates a quenching suggesting a significant interaction between MWNT and P2. SEM and TEM micrographs suggest a good dispersion and coating of P2 on MWNT surface. The Raman D/G band intensity ratio remains unchanged, and a small shift of >C═O vibration peak to lower energy suggests an interaction between P2 and MWNT. The presence of CH−π and π–π interactions between P2 and MWNT is evidenced from UV–vis, PL, Raman, FTIR, and NMR spectral results facilitating the wrapping of P2 on MWNT surface. Poly(vinylidene fluoride) (PVDF)/P2/MWNT composites (PCMx, x indicates wt % of MWNT) are prepared by solvent casting method with 0.02% (w/v) P2 and varying concentration of MWNT in DMF. The SEM and TEM micrographs show a homogeneous dispersion of MWNT/P2, and the optical micrographs indicate a loss of spherulitic morphology in the composites. FTIR spectra suggest the formation of piezoelectric β-phase PVDF and the presence of specific interaction between >C═O group of P2 and >CF2 group of PVDF. The storage modulus (G′) shows a highest increase (122%) in PCM0.5 among the PVDF/MWNT composites. The increase in Young’s modulus, tensile strength, and toughness in PCM 0.05 is two to three times higher than that without P2. Analysis of Young’s modulus data suggests a random distribution of MWNT in the composite. The PCM1 has the highest conductivity (2 × 10–2 S/cm), and the system shows a very low percolation threshold at 0.06 wt % MWNT. The conductivity data obeys the 3-D percolation model. By comparing the above mechanical property and conductivity data with that of other MWNT/PVDF composites, it is argued that the noncovalently functionalized MWNT with P2 is a better reinforcing agent.