Optothermal grid activation of microflow with magnetic nanoparticle thermophoresis for microfluidics

We report focused light-induced activation of intense magnetic microconvection mediated by suspended magnetic nanoparticles in microscale two-dimensional optothermal grids. Fully anisotropic control of microflow and mass transport fluxes is achieved by engaging the magnetic field along one or the other preferred directions. The effect is based on the recently described thermal diffusion–magnetomechanical coupling in synthetic magnetic nanofluids. We expect that the new phenomenon can be applied as an efficient all-optical mixing strategy in integrated microfluidic devices. This article is part of the theme issue ‘Transport phenomena in complex systems (part 2)’.

VISCOMETRY OF NANODISPERSE MAGNETIC LIQUIDS AND LUBRICATING OILS. 1. INSTRUMENTATION FOR RHEOLOGICAL STUDIES OF MAGNETIC NANODISPERSE LIQUID MEDIA

Анализ литературных источников показывает, что существующие вискозиметры не всегда и не полностью могут обеспечить комплексные исследования магнитных наножидкостей для научных и практических целей. Разработана конструкция магнитного ротационного вискозиметра, на котором исследования могут проводиться в широком диапазоне значений индукции магнитного поля. Магнитное поле в приборе направлено ортогонально напряжению сдвига и может изменяться от нуля до 1,7·10 А/м. Прибор имеет два измерительных зазора заполненных жидкостью, что повышает точность результатов исследований маловязких жидкостей. Вискозиметр позволяет измерять стандартные характеристики магнитных наножидкостей (коэффициент вязкости, пластическая вязкость, предельное напряжение сдвига и др.), а также изучать структурные особенности жидкостей при сдвиговых напряжениях. Скорость сдвига в жидкости может стабильно поддерживаться в широком диапазоне (1 ÷5)·10 с. Вязкость исследуемых жидкостей может изменяться от 10 Па·с до ≈ 10 Па·с. Для исследований на вискозиметре требуется небольшое количество магнитной наножидкости объемом около 3,5 см. Математическое описание процесса ламинарного течения жидкости в кольцевом зазоре вискозиметра позволило оптимизировать его геометрические размеры и получить формулы для расчета коэффициента вязкости, напряжения сдвига и скорости сдвига, используя экспериментальные данные. Analysis of the literature sources shows that the existing viscometers are not always and not completely able to provide comprehensive studies of magnetic nanofluids for scientific and practical purposes. Design has been developed of a magnetic rotary viscometer which makes it possible to carry out investigations in a wide range of the magnetic field induction. The magnetic field in the device is directed orthogonally to the shear stress and can vary from zero to 1,7·10 A/m. The device has two measuring gaps filled with liquid, that increases the accuracy of the results of studies of low-viscosity liquids. The viscometer allows you to measure the standard characteristics of magnetic nanofluids (viscosity coefficient, plastic viscosity, ultimate shear stress, etc.), as well as to study the structural features of liquids under shear stresses. The shear rate in the liquid can be stably maintained in a wide range of (1÷5)·10 c. The viscosity of the studied liquids can vary from 10 Pa·s to ≈10 Pa·s. For studies on a viscometer, a small amount of magnetic nanofluid with a volume of about 3,5 cm is required. Using experimental data, the mathematical description of the process of laminar fluid flow in the annular gap of the viscometer made it possible to optimize its geometric dimensions and obtain formulas for calculating the viscosity coefficient, shear stress and shear rate.

Size Effect of Fe3O4 Nanoparticles on Magnetism and Dispersion Stability of Magnetic Nanofluid

It is well known that magnetic nanofluids are widely applied in various fields ranging from heat transfer to miniature cooling, and from damping to sealing, due to the mobility and magnetism under magnetic field. Herein, the PFPE-oil based magnetic nanofluids with superior magnetization and dispersion stability were obtained via regulating reaction temperature. The structures of particles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The size effects of particles on the magnetism and coating effect of particles, and on the stability and saturation magnetization of the fluids were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM) and density instrument, respectively. The results indicate that the impurity phase FeOOH only appear in the sample prepared at 18°C and the average size of Fe3O4 nanoparticles reduces from 120 to 20 nm with raising reaction temperature. The saturation magnetization of Fe3O4 particles increases firstly and then reduces with increasing particle size, which is affected by the thickness of magnetic dead layer and impurity phase FeOOH. The Fe3O4 particles could be chemically coated by PFPE-acids, and the coated mass is a little affected by particle size. The stability of the nanofluids lowers while the saturation magnetization increases firstly and then decrease with increasing particle size. At reaction temperature of 60°C, Fe3O4 particles of 25 nm and the nanofluids with superior stability and saturation magnetization were obtained. Our results indicate that the control of nanoparticles size by regulating reaction temperature can be a useful strategy for preparing magnetic nanofluids with desirable properties for various potential applications.

Reliable evaluation method of heating power of magnetic nanofluids to directly predict the tumor temperature during hyperthermia

Reliable measurement of heating power of magnetic nanofluids (MNs) to accurately predict the AC heat-induction performance in tumors is highly desirable for clinical magnetic nanofluids hyperthermia (MNFH) application because it can save time for screening the performance of newly developed MNFH agent and minimize the over-use of animals dramatically. Here, a bio-mimicking phantom model, called Pseudo-Tumor Environment System (P-TES), biochemically designed by considering the external and internal critical factors related to the complex biological environments is proposed to provide a highly reliable evaluation method of heating performance of MNs for in-vivo MNFH applications. According to the experimentally analyzed results, the heating power of MNs measured using the P-TES is well accorded with the heating temperature measured in the tumors during in-vivo MNFH. This result strongly demonstrates that the proposed P-TES can be recommended as a standardized measurement method of heating performance of MNs for clinical MNFH application.