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

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.