Maria Skryabina, Lomonosov Moscow State University, Faculty of Physics, Russia
Evgeny Lyubin, Lomonosov Moscow State University, Faculty of Physics, Russia
Maria Khokhlova, Lomonosov Moscow State University, Faculty of Physics, Russia
Andrey Fedyanin, Lomonosov Moscow State University, Faculty of Physics, Russia
The dynamic and static properties of magnetic particles in a viscous nonmagnetic medium are of wide interest in science and technology. Phenomena which occur in such systems are important in manufacturing of magnetic devices, application of ferrofluids, and use of magnetic microspheres in medicine.(link (magnetic holes)).
Collective behavior of large number of micro-particles in various configurations of external magnetic field has been studied in numerous of works. But the problem of pair microparticle interaction in aqueous solution with an external magnetic field is still very poorly studied. Such forces of interaction are very small (in order of hundreds of fN) so the ability to measure and control them is of considerable interest.
Moreover the Brownian motion of single micro-particles in solution prevents the detection and measurements of the magnetic pair interaction forces. Powerful tool for studying the interaction of two Brownian particles in a liquid is a correlation analysis. In this work correlation analysis of the Brownian motion of two magnetic particles in the presence of external magnetic field is combined with the optical tweezers technique. This approach allows the detection of small pair interactions between magnetic micro-particles using their Brownian motion. Nanooptical tweezers is a fast developing technology of the weak force measurement based on the nanometer displacement registration.
Here we present a magneto-optical tweezers that contains two optical traps in a homogeneous magnetic ﬁeld. This instrument was used for studying interaction between paramagnetic particles. In experiment magnetic interactions between individual colloidal particles were directly studied. Two microscopic ferrite garnet beads were held a fixed distance apart in separate optical tweezers. The position fluctuations of the beads were measured, from which correlation and cross-correlation functions were calculated. There are two magnetic field geometry (parallel and perpendicular to line connecting particle positions) were studied. We present the numerical simulation of behavior of such system using Monte-Carlo simulation method for colloidal particles Brown movement.
Magnetic interaction between particles was detected by presence of typical anticorrelation (in parallel geometry) and correlation (in perpendicular geometry) in cross-correlation functions of particles Brown motion.
Thereby proposed method of correlation analysis combined with optical tweezers technique is a new powerful instrument used for studying of interaction between individual microparticles suspended in liquid medium. This approach provides registration of femtonewton scale forces.
Miss. Maria Skryabina
Lomonosov Moscow State University, Faculty of Physics
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