The effect of long time exposure to light of a water-based ferrofluid on its low frequency complex magnetic permeability

The paper reports on the effect of prolonged exposure to light of a water-based ferrofluid, with magnetite particles, double stabilized with oleic acid, on its low frequency complex magnetic permeability. The investigated ferrofluid was divided into three samples and placed in identical transparent glass vials. The reference sample, denoted by SR was kept in dark (in the laboratory), other sample, denoted by SL, was exposed to the light of a table lamp, with LED bulb (in the laboratory) and the third sample, denoted by SG, was exposed to natural sunlight, in a garden (subjected to the succession of days and nights as well as to the weather conditions). The duration of exposure to light was 80 days, during the summer. Complex magnetic permeability measurements over the frequency range 1 kHz-2 MHz show that after exposure to light both SL and SG samples exhibit Brownian maxima, unlike the reference sample, which has no maximum. Dynamic light scattering measurements show that in all three ferrofluid samples, the magnetic nanoparticles are mainly organized in condensed phase droplets and after exposure to light, the diameter of agglomerations increases. The change in the magnetic permeability spectrum of the investigated samples is explained based on the change in the local structure of ferrofluids, due to the electron-hole pairs resulted by photoelectric effect in magnetite, which affect the electrochemical balance of the colloidal system.

Automated summary

This study investigates the effect of prolonged exposure to light on the low-frequency complex magnetic permeability of a water-based ferrofluid with magnetite particles. Results show that exposure to light causes the samples to exhibit Brownian maxima, unlike the reference sample. The change in magnetic permeability spectrum is attributed to alterations in the local structure of ferrofluids induced by electron-hole pairs resulting from the photoelectric effect in magnetite.