Effects of copper filler sizes on the dielectric properties and the energy harvesting capability of nonpercolated polyurethane composites

Abstract

International audienceNonpercolated composites based on polyurethane (PU) filled with low concentrations copper (Cu) powders of varying sizes were studied as electrostrictive materials for mechanical energy harvesting. The dispersion of the fillers within the polymeric matrix was investigated by scanning electron microscopy, and results showed a relatively homogeneous dispersion for the microsized fillers and the existence of agglomerates for their nanosized counterparts. Differential scanning calorimetry measurements displayed that there occurred no interaction between the polymeric matrix and the microsized fillers whereas the nanosized fillers slightly enhanced the glass transition of the soft segments of PU and significantly affected the recrystallization temperature. The dependence of the dielectric properties of the composites as a function of the filler volume fraction and filler size was investigated over a broad range of frequencies, showing an increase in the permittivity when fillers were used. This increase was more pronounced for the composites containing nanosized fillers. The measurement of the harvested current and of the harvested power also demonstrated an enhancement of the energy harvesting capability when nanofillers were employed. From the experimental data, it appeared that the electrostrictive coefficient Q was not proportional to the inverse ratio of the permittivity and the Young modulus for the studied composites. Finally, analytical modeling of the harvested current and of the harvested energy offered an accurate description of the experimental data

Fillers in advanced nanocomposites for energy harvesting

“…Nanosized fillers increase the permittivity more than micro-sized fillers, and the percolation threshold is lower (Putson et al, 2011). The addition of 0.1 wt% GO to PVDF significantly increases the dielectric constant.…”

“…PU was also applied (Putson et al, 2011) as a possible polymer matrix when filled with nanosized copper. PU was also applied (Putson et al, 2011) as a possible polymer matrix when filled with nanosized copper.…”

“…Nanosized particles added to a matrix can change its properties in a more pronounced way than microsized fillers, which was proven by the significant increase in crystallization temperature and slight increase in glass transition temperature for nanosized copper powders added to PU (Putson et al, 2011). On the basis of the melting thermograms of PVDF using differential scanning calorimetry (He et al, 2011), two melting peaks were observed due to the presence of two phases (alpha [a] and beta [b]) with different crystal structures.…”

“…Several studies have suggested that the smaller particle sizes, usually on the nanoscale level, are responsible for an enhancement in energy-harvesting performance in comparison to fillers at the microscale level (Putson et al, 2011). Several studies have suggested that the smaller particle sizes, usually on the nanoscale level, are responsible for an enhancement in energy-harvesting performance in comparison to fillers at the microscale level (Putson et al, 2011).…”

Electrostrictive polymers for mechanical energy harvesting

“…The effective loss tangent shows the highest value for low frequencies due to the electric conduction. 38,39 Losses then decrease with the frequency except for the frequencies where polarization mechanisms disappear. 33 Maximum Energy Harvesting For every energy-harvesting technique presented in the ''Energy-Harvesting Techniques'' section, it can be seen that the electrostrictive coefficient M appears to be an important parameter to increase the scavenging abilities of the system.…”