This paper presents a new magnetic method for microfluidic visualization using low-density, highly buoyant, strongly reflective and magnetically responsive microcrystals. Microcrystal suspensions were passed through a channel with or without exposure to a magnetic field using a permanent magnet. This approach enhanced the contrast of the flow patterns. We also observed the movements of microcrystals in a paramagnetic aqueous solution containing MnCl2. In the paramagnetic solution, guanine crystals showed migration both to and from the higher magnetic fields in the microfluidic path. In contrast, microcrystals with diamagnetic susceptibility caused a stream only towards lower magnetic fields. Flow pattern measurements were also carried out using microcrystalline cellulose and boron nitride crystals. The methods developed here are expected to be useful for advancing microfluidic mechanics through the use of magnetic field effects on microcrystals in liquids.
The present study focused on the vibration of micro crystal particles of guanine due to Brownian motion. The organic particle has a refractive index of 1.83 and caused a flickering of light. To test the possibility of using magnetic properties under wet conditions, changes in the frequency of particle vibration by applying magnetic fields were investigated. At first, we found that the exposure at 5 T inhibited the flickering light intensities and the particle vibration slightly decreased. Next, we carried out a high speed camera measurement of the Brownian motion of the particle with a time resolution of 100 flame per second (fps) with and without magnetic field exposures. It was revealed that the vibrational speed of synthetic particles was enhanced at 500 mT. Detailed analyses of the particle vibration by changing the direction of magnetic fields versus the light source revealed that the Brownian motion’s vibrational frequency was entrained under magnetic fields at 500 mT, and an increase in vibration speed to 20Hz was observed. Additional measurements of light scattering fluctuation using photo-detector and analyses on auto-correlation also confirmed this speculation. The studied Brownian vibration may be influenced by the change in mechanical interactions between the vibration particles and surrounding medium. The discovered phenomena can be applied for molecular and biological interactions in future studies.
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