Effective vibration sensing nanocomposite sheets based on Poly(vinylidene fluoride-co-hexafluoropropylene) matrix and SrTiO3 nanoparticles grafted with 2,2,2-trifluoroethyl methacrylate nanoscale coating

Abstract

Structural, thermal and mechanical properties of poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP))/strontium titanate (ST) nanocomposites with different weight ratios were investigated in this research. ST particles were modified for the first time by poly(2,2,2-Trifluoroethyl methacrylate) (PTFEMA) nanoscale coating. The successful polymerization from the surface using atom transfer radical polymerization (ATRP) approach was investigated using 1H nuclear magnetic resonance and gel permeation chromatography, by means of monomer conversion and molecular weight/polydispersity index, respectively. The presence of the nanometer thin PTFEMA coating was confirmed using transmission electron microscopy. Scanning electron microscope with energy-dispersive spectroscopy was used for evaluation of the individual elements such as carbon, fluorine and oxygen. Fabricated nanocomposites were thoroughly characterized using Fourier transform infrared spectroscopy to show, that even a small amount of ST or ST-PTFEMA decreased the amount of β-phase content compared to the pristine polymer. However, with higher filler amounts, β-phase remained same or slightly decreased. Mechanical properties and glass transition temperature (Tg) were determined by dynamic mechanical analysis. For the pure polymer at 1 Hz the Tg was −35.1 °C, while for nanocomposites Tg were within the range of −35.9 to −35.0 °C for those with ST and −37.1 to −35.8 °C for those with ST-PTFEMA, showing the reinforcement of the fabricated nanocomposites. The tensile test showed that addition of 5 wt % of ST-PTFEMA allowed nanocomposite to keep almost same strain at break (940 ± 40 %) value as pristine P(VDF-HFP) (990 ± 30 %), while nanocomposite with 5 wt % of neat ST value decreased to (640 ± 20 %). Furthermore, strain at break value of nanocomposites with increasing content (10 and 20 wt%) of neat ST significantly dropped, while those with ST-PTFEMA analogues were able to keep higher values even with increasing content of those particles, thus those are suitable for further treatment techniques such as additional stretching. Finally, the vibration sensing activity of the nanocomposites were measured, where highest d33 was achieved by nanocomposite with 5 wt% ST-PTFEMA 21.4 ± 1.3 pC/N which was significantly higher than d33 for neat PVDF 14.4 ± 1.4 pC/N as well as corresponding non-modified analogues showing 18.6 ± 1.9 pC/N.