Ferrofluid-based micromixers have been widely used for a myriad of microfluidic industrial applications in biochemical engineering, food processing, and detection/analytical processes. However, complete mixing in micromixers is extremely time-consuming and requires very long microchannels due to laminar flow. In this paper, we developed an effective and low-cost microfluidic device integrated with microscale magnets manufactured with neodymium (NdFeB) powders and polydimethylsiloxane (PDMS) to achieve rapid micromixing between ferrofluid and buffer flow. Experiments were conducted systematically to investigate the effect of flow rate, concentration of the ferrofluid, and micromagnet NdFeB:PDMS mass ratio on the mixing performance. It was found that mixing is more efficient with lower total flow rates and higher ferrofluid concentration, which generate greater magnetic forces acting on both streamwise and lateral directions to increase the intermixing of the fluids within a longer residence time. Numerical models were also developed to simulate the mixing process in the microchannel under the same conditions and the simulation results indicated excellent agreements with the experimental data on mixing performance. Combining experimental measurements and numerical simulations, this study demonstrates a simple yet effective method to realize rapid mixing for lab-on-chip systems.

The thermal decomposition kinetics of strontium nitrate, Sr(NO3)2 was studied by thermogravimetry using non-isothermal experiments. For the kinetic analysis, the TG/DTG data obtained in the temperature range 30-850 ºC at different heating rates (5, 10, 15 and 20 K/min) in the nitrogen atmosphere were processed by model fitting and model free methods. The thermal decomposition of Sr(NO3)2 occurred in a single stage without the formation of intermediate nitrite. The average apparent activation energies of thermal decomposition of Sr(NO3)2 as determined by Straink, Flynn-Wall-Ozawa, KAS and Friedman methods are 344.37, 341.39, 344.05 and 362.62 kJ/mol, respectively. The value of the invariant activation energy (344.83 kJ/mol) obtained by Invariant kinetic parameter method is in a good agreement with integral isoconversional methods. The appropriate conversion model of the process selected by means of the master plot method is "Diffusion model (D4)".

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Separation of microparticles and cells serves a critical step in many applications such as in biological analyses, food production, chemical processing, and medical diagnostics. Sorting on the microscale exhibits certain advantages in comparison to on the macroscale as it requires minuscule sample or reagents volume and thus reduced analysis cycle time, smaller size of devices and lower fabrication costs. Progresses have been made over time to improve the efficiency of these microscale particle manipulation techniques. Many different techniques have been used to attain accurate particle sorting and separation in a continuous manner on the microscale level, which can be categorized as either passive or active methods. Passive techniques achieve accurate manipulation of particles through their interaction with surrounding flow by carefully designed channel structures, without using external fields. As an alternative, active techniques utilize external fields (e.g. acoustic, electronic, optical and magnetic field etc.) to realize desired pattern of motion for particles with specific properties. Among numerous active methods for microfluidic particle sorting, the magnetic field has been widely used in biomedical and chemical applications to achieve mixing, focusing and separating of reagents and bio-particles. This paper aims to provide a thorough review on the classic and most up-to-date magnetic sorting and separation techniques to manipulate microparticles including the discussions on the basic concept, working principle, experimental details, and device performance.

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