Cluster formation in ferrofluids induced by holographic optical tweezers

Abstract

Holographic optical tweezers were used to show the interaction between a strongly focused laser beam and magnetic nanoparticles in ferrofluid. When the light intensity was high enough, magnetic nanoparticles were removed from the beam center and formed a dark ring. The same behavior was observed when focusing vortex or Bessel beams. The interactions between two or more separated rings of magnetic nanoparticles created by independent optical traps were also observed.

Observation of magnetic nanoparticles ring formation and dynamics with fast video camera

“…The process of ring creation reported in [12] is very fast, so we could not observe how the ring was developing. The process of ring disappearing is relatively slow and smooth.…”

“…Moreover, the "big tail" is being created (a strong tail which is brighter than others and almost always opens - Fig. 4) [12]. Interestingly, if there is a dark crescent spot inside the ring, the big tail starts always on the opposite side.…”

“…Interestingly, if there is a dark crescent spot inside the ring, the big tail starts always on the opposite side. After the ring was formed, it does not remain stable [12]. Its vibrations were observed with a high speed camera (see also movie file 1: ring creation in slow motion -100× slowed).…”

“…In [1] the reader can find a review of optical properties of ferrofluids. In paper [12] we reported on the new phenomenon discovered when investigating ferrofluids with holographic optical tweezers. The advantages of a holographic system are high energy density and the possibility to work with many different optical traps at the same time.…”

Study of Faraday effect on Co1-xZnxFe2O4 nanoferrofluids

“…To avoid the aggregation of nanoparticles, they have to be covered with a suitable surfactant. Optical property of ferrofluids can be altered by external applied magnetic field [2]. Structural reorientation of the nanoparticles suspended in a magnetic colloid brings out magneto-optic properties [3], which are used in developing optical sensors [4], photonic devices [5], etc.…”