I want to align magnetite nanoparticles (300 nm in size) under the influence of a magnetic field. I am having trouble in deciding the strength of the magnetic field required to do so. Is there any way to analytically calculate how much minimum field strength would I require to move the magnetite nanoparticles from their rest position? If that's possible, then I can order bar magnets of adequate magnetic field strength.
Thanks in advance.
It depends what kind of motion you want to obtain.
1) In homogeneous magnetic field B there is no translation of magnetic nanoparticles, the nanoparticles with magnetic moment m can only rotate due to non-zero torque T:
T=m x B (vector notation)
It can be now compared to the torque due to viscosity of a fluid acting on spherical particle with radius R:
Tv=-8*pi*R3*n*omega (in vector notation)
where omega is angular velicity
n is a viscosity
pi is obviously equal to 3.14....
Thus to align all particles according to field direction::
B=8*pi2*R3*n/m*t
t - is a time
Concluding: minimum field strength depends on... the time t you can wait or the time of solidification of your polymer.
2) translational motion of magnetic nanoparticles can be only obtained in inhomogeneous field. Thus the effect depends of the field gradient gradB.
The force acting on magnetic moment m is:
F=grad(m*B)
The drag force according to Stokes law is:
Fd=6*pi*n*R*v
where v is a velocity of a particle
Thus:
grad(m*B)=6*pi*n*R*s*t
where s is a distance you want to shift your particles and t is a time (solidification time of a polymer).
Best regards,
Bartek
Dear Bartlomiej,
Thank you very much for your quick response. I wanted to translate my magnetite nanoparticles to align them in a particular fashion. The information you provided is relevant to the question at hand. I shall definitely look into it.
Best regards,
Anvay.
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