PVDF-based coatings with CNT additions for strain monitoring of mortar substrates subjected to bending

Abstract

Sensing coatings are rapidly entering the field of non-destructive tests. While cement-based composites are proving an excellent interaction with new/recent structures, polymer-based coatings, already employed for structural retrofitting purposes, can provide a valuable alternative. This study investigated the production, application, and use of poly(vinylidene fluoride) (PVDF) coatings. A 10w/v% PVDF-to-solvent ratio became the best trade-off between electrical conductivity and bond strength with the substrate. Different concentrations of Carbon Nanotubes (CNT) were investigated: 0.05, 0.10, 0.25, 0.50, and 0.75% by weight of PVDF. The conductive PVDF-CNT composites were brushed on the casted mortar beams with screws embedded as electrodes. The mortar beams and attached polymer coatings were then subjected to bending stress. The Gauge Factor was obtained by comparing the substrate’s strain with the coating’s electric response. The sensing intervals in the Fractional Change of Resistance-strain curves varied in relation to the CNT concentration. For instance, adding 0.50w/v% of CNT gave the highest sensitivity up to 0.2‰ strain, followed by a lower – still sufficient – gauge factor. PVDF-based coatings with CNT additions of 0.25 and 0.75w/v% witnessed a comparable sensing performance in the same strain limits, abruptly increasing and finally stabilizing to a low gauge factor. In contrast, both 0.05 and 0.10w/v% resulted in a low monitoring potential overall. The varying sensing zones experienced by the coating were attributed to the microscopical behavior of CNT within the PVDF matrix. In conclusion, the results highlighted the potentiality of polymeric coatings for sensing, monitoring, and inspection of concrete structures.

Piezoelectric Elements with PVDF–TrFE/MWCNT-Aligned Composite Nanowires for Energy Harvesting Applications

“…The measured current w 1435 µA, which is, to the best of the authors' knowledge, the highest reported value fo composite between CNT, MWCNT, and PVDF, or PVDF-TrFE. The highest current va found in the literature was 10 nA for 0.75 wt% of CNT, which was added to PVDF for strain monitoring device [38]. The effect observed in our work can be ascribed both to presence of MWCNT and nanostructuring, serving as the superposition and multiply the effects in a single composite nanowire.…”

“…Due to the existing contact resistance, the PVDF-TrFE/MWCNT composite can exhibit an initial misalignment of the piezoelectric dipoles at lower loads. This misalignment can lead to a non-linear response, but as the load increases, the dipoles align more uniformly, leading to more linear behavior [38].…”

“…Based on a previous investigation of a vacuum-sputtered potassium niobate ceramic material that filled the nanopores of anodic aluminum oxide [33], it can be concluded that the aspect ratio of the nanoformations is of great importance for the optimization of the piezoelectric yield. It was demonstrated in [38] that the piezoelectric voltage increased with the length of the KNbO 3 nanowires. This correlation suggests that the greater volume of the piezoelectric material in longer nanowires may contribute to the higher voltage output.…”