Properties Of Magnetic Fluids Research Articles

Control Voltage Effect on Operational Characteristics of Vehicle Magnetorheological Damper

Considering the increasingly large-scale application of magnetic fluids in various industries, we can confidently state that in the near future magnetorheological dampers will be widely used in adaptive automotive suspensions due to their operational flexibility and simplicity of controlling damping forces by changing the magnetic fluid properties according to parameters of surrounding electromagnetic field. The antivibration efficiency during operation is achieved by regulating the hydraulic resistance of the “magnetic” shock absorber by applying voltage to the windings of its coil. In addition to the physical properties of the oil used in the “magnetic” shock absorber, the viscosity of the working magnetorheological fluid is greatly influenced by the shape of the control signal. The paper focuses on the theoretical aspects of constructing a mathematical model of ac magnetorheological damper and presents the results of a computer experiment to assess effectiveness of its use as part of the adaptive suspension a passenger vehicle. In this case, the actual parameters of the “magnetic” shock absorber, used in modeling the dynamic process, were determined experimentally on a test bench, and the adequacy of the developed mathematical model was confirmed by the results of a semi-natural experiment. Using a verified model, the magnetorheological damper characteristics were obtained and compared for various forms of control signal, including rectangular voltage pulses of various frequencies and duty cycles, sinusoidal pulses and constant voltage signals. The analysis of the antivibration efficiency was carried out on the basis of the developed “quarter” model of a semi-active car suspension with a verified submodel of a magnetorheological damper integrated into its structure. Moreover, the simulation scenarios were based on the selected strategy for controlling the voltage supplied to the windings of the “magnetic” shock absorber. As the results of theoretical and experimental studies have shown in terms of energy consumption, expansion of the working area of the damping characteristic and achieving smooth control of the damping force, the most effective is the use of a sinusoidal pulse voltage signal in the control circuit, which ensures a reduction in both the amplitude and damping time of oscillations. However, when de-signing and manufacturing a controller, creating a pulse modulator for generating sinusoidal pulses coinciding in phase and frequency with the vibrations of the car body is very difficult due to the random nature of external disturbances from the road surface. When a constant voltage is applied to the magnetorheological damper winding, the damping properties of the suspension are also improved compared to the basic design based on a traditional hydraulic shock absorber. Moreover, there is a proportional relationship between the voltage supplying the damper, the amplitude and damping time of the vibrations of the car body is observed. An increase in the control signal voltage from 1 to 2 V leads, in comparison with passive control of a magnetic shock absorber, to a decrease in the maximum amplitude of vibrations of the car body by 6.25 and 11.25 %, respectively, and a decrease in the vibration damping time by 0.72 and 1.41 s.

Research on preparation and stability of high viscosity carbon nanotube-modified PAO20-based magnetic fluids

The preparation of high-performance magnetic fluids with high viscosity, high saturation magnetization and high stability, has remained a pivotal challenge limiting the advancement of associated applications. In the present study, we synthesized modified magnetic nanoparticles through an innovative approach combining in-situ carbon nanotube (CNT) generation with chemical co-precipitation. These nanoparticles were then co-coated with OA/PIBA, resulting in the preparation of advanced PAO20-based magnetic fluids. The effects of CNT modification on particle microstructure and magnetic properties were studied by transmission electron microscopy and vibrating sample magnetometer, the magnetoviscous properties of magnetic fluids were studied by a rotating rheometer equipped with a magnetic field module, and the stability of the prepared magnetic fluids under a strong magnetic field was tested by a self-made LC oscillation circuit. The results show that the saturation magnetization of the prepared magnetic fluids surpasses 32 emu/g, while their viscosity reaches a remarkable 6625 mPa·s (at 0.24 T, 100 1/s shear rate and 25 °C), which is significantly higher than that of traditional magnetic fluids (usually about 100 mPa·s). Furthermore, when exposed to a 0.6 T magnetic field, the magnetic fluids could exhibit Rosensweig instability that persists for over 468 h. The stability is at least 93 times superior to that of unmodified PAO20-based magnetic fluids. Based on these encouraging results, it can be fully predicted that the CNT-modified PAO20-based magnetic fluids developed in this study will play a pivotal role in various applications, including sealing, lubrication, and vibration reduction. Their exceptional properties will hold immense promise for numerous engineering applications.

A Double-Rotating Ferrofluid Vane Micropump with an Embedded Fixed Magnet

This paper introduces the prototype design, magnetic field analysis and experimental test of a double-rotating ferrofluid vane micropump with an embedded fixed magnet. The micropump is based on the working principle of a positive-displacement pump, as well as the magnetic characteristics and flow properties of magnetic fluid. Through the numerical analysis of the pump cavity magnetic field and the experimental test, the structural parameters of the micropump are optimized reasonably. The pumping flow and pumping height of the micropump were characterized at different driving speeds. The maximum pumping flow rate is approximately 410 μL/min, and the maximum pumping height is approximately 111.4 mm water column. The micropump retains the advantages of simple structure, easy manufacture, flexible control, self-sealing, self-lubrication, low heat production, etc., and can block the pumped liquid backflow. The resulting double-rotating ferrofluid blades can improve pumping efficiency and pumping capacity, and can improve pumping reliability and stability to a certain extent.

On the dependence of the thermal module of elasticity of a two-component magnetic fluid on frequency, concentration and magnetic field

Purpose. Study of the dependence of the thermal modulus of elasticity of a two-component magnetic fluid on the magnitude of the magnetic field strength, the frequency of external disturbance and the volumetric concentration of magnetic particles.Method. The research method is based on the kinetic theory of liquid systems. Based on previously constructed kinetic equations for one-particle and two-particle distribution functions and a microscopic expression for the heat flux vector, an explicit dynamic expression for the thermal modulus of elasticity of magnetic fluids is obtained. In fast processes in liquids, heat transfer occurs in waves and their propagation is similar to the propagation of second sound in helium II. The thermal modulus of elasticity in liquids appears at high frequencies and ensures the propagation of second sound. The expression for the thermal modulus of elasticity consists of potential and kinetic parts, taking into account structural and translational relaxation processes, respectively. To study the thermoelastic properties of magnetic fluids, appropriate expressions of potential interaction energies were selected for each subsystem, allowing for numerical calculations.Results. Numerical calculations of the frequency and concentration dependence of the dynamic thermal modulus of elasticity in the presence of an external magnetic field in a kerosene-based magnetic fluid were carried out. The calculation results show that an increase in the influence of external disturbances leads to a nonlinear increase in the thermal modulus of elasticity in the magnetic fluid. An increase in the volume concentration of magnetic particles and an increase in the magnetic field strength also led to a nonlinear increase in the thermal modulus of elasticity in the magnetic fluid.Conclusion. It has been established that, due to taking into account translational and structural relaxation processes, the region of frequency dispersion of the thermal elastic modulus is wide. Numerical calculations carried out at different values of the external magnetic field and the volume concentration of magnetic particles showed that although an increase in the magnetic field and concentration of magnetic particles leads to an increase in the thermal modulus of elasticity, their increase does not affect the change in the frequency dispersion region.

Inversion of magnetic diameter distribution of magnetic fluids under high and low temperatures

The magnetic diameter is a crucial factor affecting the magnetic properties of magnetic fluids. The magnetic diameter distribution can be estimated based on the magnetic properties. However, the magnetic dipole interaction of magnetic nanoparticles (MNPs) and the variation of the magnetic diameter with temperature have received relatively little attention in previous research. Hence, this research proposes the AP-MMF1-L method to inverse the magnetic diameter which considers the magnetic dipole interaction and derives the magnetic diameter at different temperatures. Firstly, the AP-MMF1-L uses the least square method between the first-order modified mean-field Langevin function (MMF1-L) and the measured magnetization curve as the objective function. Meanwhile, the hybrid Artificial bee colony-particle swarm (AP) optimization algorithm is introduced to inverse the optimal magnetic diameter distribution. Secondly, the hydrodynamic diameter distribution experimental values are compared with the theoretical values, demonstrating the AP-MMF1-L method obtains accurate inversion results of the magnetic diameter distribution when compared to other models. Finally, the arithmetic mean of the magnetic diameter at different temperatures is investigated, revealing a decreasing trend as the temperature rises, approximately following a linear distribution. The AP-MMF1-L provides a novel and effective tool for accurately determining the magnetic diameter of the MNPs across various temperatures.

In Ukrainian

The purpose of the review is to find, generalize and analyze scientific data related to the specifics of the interaction of chemotherapeutic official drugs and nanocomposites based on them with malignant cells and tumors, primarily characterized by the emergence of drug resistance, the determination of promising directions and ways to overcome it, and the creation of new effective nanocomposite remedies for use in antitumor chemotherapy. The given data indicate the relevance of the topic. Targeted studies of the resistance of malignant cells and neoplasms to chemotherapeutic drugs have been carried out since the 1990s. The majority of works were performed according to the methodology, that involves the traditional use of chemotherapeutic drugs. In these works, the principle of the multifactorial nature of resistance was determined, the processes and mechanisms of its implementation were studied, related to the reduction of the accumulation of the chemotherapeutic drug in cells, the increase in the activity of detoxification systems, the strengthening of DNA repair processes, the reduction of apoptosis, and autophagy. A number of promising substances and influencing factors contributing to overcoming of resistance have been identified. However, the discovered ways to overcome the resistance of malignant cells and neoplasms to the corresponding drugs are at the stages of laboratory, preclinical, or, in the best case, clinical research. At the same time, it is not excluded that the use of the latest highly effective chemotherapeutic drugs will lead to the emergence of new mechanisms of resistance. Thus, at this time the results of research on the traditional use of chemotherapeutic drugs constitute a significant fundamental and practically important development regarding the determination of mechanisms of drug resistance, however, the problem of its medicinal overcoming remains far from being solved, and the used approaches give the impression of dead ends. With the development of nanotechnology, new scientific directions have been initiated and a significant amount of researches has been carried out, devoted to the creation and search for promising applications in oncology of nanocomposites based on bioinert, biocompatible and bioactive nanoparticle materials and modern chemotherapeutic drugs. It should be emphasized that all these works contain data indicating the advantages of introducing nanocomposite drugs into clinical practice, compared to the use of chemotherapeutic drugs in traditional forms. Against this background, purposeful researches are distinguished carried out by scientists of O.O. Chuiko Institute of Surface Chemistry of National Academy of Sciences of Ukraine and R.E. Kavetsky Institute of Experimental Pathology, Oncology and Radiobiology of National Academy of Sciences of Ukraine in the field of creation of modern polyfunctional nanocomposite chemotherapeutic agents for use in antitumor therapy, capable of overcoming drug resistance of malignant cells and neoplasms. So, at O.O. Chuiko Institute of Surface Chemistry of National Academy of Sciences of Ukraine for the first time magnetic fluids were synthesized containing antitumor drugs cisplatin, doxorubicin, gemcitabine, corresponding antibodies, their physicochemical properties were studied, and parameters for standardization were determined. At R.E. Kavetsky Institute of Experimental Pathology, Oncology and Radiobiology of National Academy of Sciences of Ukraine the antitumor properties of magnetic fluids were studied. On the basis of magnetic fluid with cisplatin, the first native magnetosensitive oncological drug "Feroplat" has been proposed, which has no analogues in the world. Feroplat is a standardized tool for increasing the effectiveness of chemotherapy and overcoming drug resistance of malignant neoplasms, intended for the delivery of cytostatics directly to the tumor tissue. This ensures its maximum entry into the cells and helps to increase the therapeutic effect. In order to introduce "Feroplat" into production and clinical practice, its preclinical tests were successfully performed. The analysis of the given data indicates the priority of works in the field of creation of new nanocomposite chemotherapeutic drugs for use in antitumor therapy, capable of overcoming drug resistance of malignant cells and neoplasms. The facts of overcoming the drug resistance of malignant neoplasms to cisplatin with the new native oncological drug "Feroplat", as well as high indicators of cytotoxic / cytostatic activity of nanobiocomposites based on saline solution, magnetite and cisplatin, doxorubicin, gemcitabine, etc., may indicate the fundamental need to change approaches to the use of modern antitumor chemotherapeutic agents – by replacing their traditional molecular forms with appropriate nanocomposite forms.

Failure mechanism of magnetic fluid seal for sealing liquids

Magnetic fluid seals are contact-free rotary seals widely used to seal gas and vacuum. However, their effectiveness declines when utilized to seal liquids due to the inherent incompatibility and instability at the interface between the two liquids. The underlying mechanism for this premature failure remains incompletely comprehended, posing a significant challenge to their widespread use for sealing liquids. Here we demonstrate a novel pole structure featuring a non-magnetic shaft, which creates a closed magnetic circuit without requiring the magnetic circuit to pass through the rotating shaft. This innovative approach enables the observation of the failure processes of the seal through a hollow transparent shaft, utilizing an endoscope. The results show that the static seal failure occurrs in two stages: extrusion, infiltration, and magnetic fluid barrier rupture. In the first stage, a leakage channel opens cyclically, whereas in the second stage, the seal leaks completely once the critical pressure is surpassed. Dynamic failure arises from the intricate interplay between dissolution, extrusion, and interface instability. Upon attaining the critical speed, the flow at the interface transitions from laminar to turbulent, leading to apparent delamination fluctuations. At this point, the magnetic fluid film becomes unstable and instantly leaks from the seal upon exceeding the critical speed. This research has unveiled crucial inducing factors for seal failure that have significant implications for the design of liquid seals. The intricate and complex nature of the failure mechanism emphasizes the need for a comprehensive understanding of the interplay between the seal design, magnetic fluid properties, and operating conditions to develop efficient liquid seals with superior performance.

Study of the Tribological Properties of Magnetic Fluid under the Surface Effects with Magnetic-pole Magnetic-groups

The tribological characteristics of the magnetic fluid are studied with the change of multi-pole distribution in this paper. The maximum magnetic field strength and its gradient on the surface of the magnetic-group are analyzed by the finite element analysis of the magnetic field strength distribution at the same magnetic-group with the area ratio of 30%. The research results show that the matching distribution among N-S magnetic-pole groups at the same pole area ratio of 30% has less influence on the magnetic specimen surface, but the magnetic field distribution of magnetic-pole with the rectangular permanent magnet in the annular friction surface has the optimal range of magnetic field distribution design for specific magnetic fluid lubrication, in which pole group specimen 5 is the best magnetic-pole magnetic-group combination for friction reduction, and specimen 1 is the second best.

­­­­PARTICLE SIZE DEPENDENCE MAGNETIC PROPERTIES OF NANOFLUIDS BASED ON MAGNETITE NANOPARTICLE: A COMPUTER SIMULATION STUDY

Magnetic nanofluids are an outstanding candidate for biomedicine research. This is because their magnetic properties play a significant role in evaluating the effectiveness of clinical applications in biomedicine. Besides, that is influenced by many factors, the most important of which is particle size. In this article, we present a simulation study to assess the effect of particle size on the magnetic properties of magnetic fluids which contain the magnetite ( Fe 3 O 4 ) nanoparticles ensemble with their physical size variation between 2 nm and 20 nm (Critical size range for biomedical applications). These results show that the magnetic properties of microfluidics strongly depend on the size of the component nanoparticles. In addition, they are also compared with experimental results reported by other authors recently, showing good agreement and providing some valuable predictions.

Influence of magnetic particles aggregation on rheological properties

The magnetic particles can form aggregates because of magnetic forces, which will cause the change of rheological properties of magnetic fluid. The viscosity of the magnetic fluid and the starting torque of the sealing device were measured in experiments, the results shown that the viscosity and the starting torque are closely related to the aggregates, in addition, shear rate, magnetic field intensity, temperature and standing time are important factors affecting the formation of aggregates. The interaction theory of magnetic particles shown that magnetic particles can spontaneously form unstable aggregates without magnetic field, while aggregates formed in magnetic field have more stable structures. If the magnetic field increases gradually from zero, the spontaneously formed aggregates will undergo a process of destruction and reconstruction, eventually grow into stable aggregates, at the same time, the single domain particles will also be gathered into new aggregates.

Viscometer for investigating the viscosity of magnetic fluid media

The rational application of magnetic fluids in various technical systems requires their stability analysis, hydrodynamic particle size, dissipative processes in the colloid control. The existing viscometers do not fully meet all requirements, in particular, they do not allow research in a magnetic field of given magnitude and certain topography. It is proposed to determine rheological properties of magnetic fluids using rotary viscometer, in which two measuring gaps are structurally designed and filled with studied fluid, which is important for calculating characteristics of low viscosity magnetic media. The device design implements practically homogeneous magnetic field, varying within wide range and directed perpendicular to liquid shear stress. The device allows to steadily maintain shear rate in medium under study, and to determine viscosity with a sufficiently large change. A small magnetic fluid volume is required to estimate rheological characteristics. The accuracy of measurements of the internal friction force, device heating temperature, coaxial cylinders rotation speed and magnetic field inside investigated medium meet the requirements of international standards. Laminar fluid flow process in the device gap is described mathematically. This made it possible to justify the construction geometrical dimensions in order to increase the measurements and determine rheological properties of low-viscosity magnetic materials. The formulas for calculation of Newtonian fluid viscosity coefficient, shear stress and shear rate based on experimental data were obtained.

An error analysis of a rheological study of magnetic nanofluids on a rotational viscometer

The paper considers metrological instrumentation for studying the rheological properties of magnetic fluids. It also presents the design of a magnetic coaxial viscometer. There is a metrological analysis of the factors that affect the measurement accuracy. Errors are systematized into 2 main groups: method and instrumental. The authors analyse the contribution of each group to the total metrological error. It is established that the temperature instability of the liquid under study and the error in determining the level of the liquid in contact with the measuring cylinder have the greatest effect on the measurement results. There is a theoretical assessment of the instrument error and its minimum value. The authors propose the main directions for improving the viscometer design. They also show the possibility of a significant reduce in the total measurement error by calibrating the device. There are comparative studies of experimental and reference liquids indicating good accuracy and reliability of experimental data.

Cobalt nanoparticles synthesizing potential of orange peel aqueous extract and their antimicrobial and antioxidant activity

The ability of cobalt nanoparticles (CoNPs) to absorb electromagnetic waves led to their use as potential biomedical agents in recent years. The properties of magnetic fluid containing cobalt nanoparticles are extraordinary. Hence, this research was designed to evaluate the Co(NO3)2 reducing the potential of orange peel aqueous extract and assessed their antimicrobial and antioxidant activities. The aqueous extract derived from orange peel had the potential to fabricate the CoNPs from 1 M Co(NO3)2 and the synthesized CoNPs were successfully characterized by standard nanoparticles characterization techniques such as UV–vis spectrophotometer, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscope (SEM), and Dynamic light scattering (DLS) analyses. The FTIR analysis revealed that the synthesized CoNPs were capped with active functional groups. It was characterized by predominant peaks corresponding to carbonyl (CO), amide (CO = ), and C–O of alcohols or phenols. The size and shape of CoNPs were found as 14.2–22.7 nm and octahedral, respectively, under SEM analysis. Furthermore, at increased concentration, the CoNPs demonstrated remarkable antimicrobial activity against common bacterial (Escherichia coli, Staphylococcus aureus,Bacillus subtilis, and Klebsiella pneumoniae) and fungal (Aspergillus niger) pathogens. Furthermore, these CoNPs also showed considerable in-vitro antioxidant activities against various free articles such as 2,2-diphenyl-1-picrylhydrazyl (DPPH), and Hydrogen Peroxide (H2O2). These results suggest that OP aqueous extract synthesized CoNPs possess considerable biomedical applications.

Distribution functions of magnetic moments and relaxation times for magnetic fluids exhibiting controllable microstructure evolution

The paper presents experimental and numerical studies of laboratory magnetic fluid samples that differ significantly from each other by dispersion compositions (particle size distributions). We propose and justify a new technique for describing the magneto-granulometric properties of magnetic fluids. Our approach is based on the analysis of distribution functions of magnetic moments and their relaxation times. It can be used to determine the magnetic response of any magnetic fluid with arbitrary particle size distribution f(x) and arbitrary microstructure, including magnetic fluids undergoing phase transition. No intermediary representation of the f(x) function is needed. It is shown that a priori standard distribution functions f(x) cannot describe the ferrofluid microstructure features, specifically those related to the formation of nanoparticle aggregates. The distributions of magnetic moments and their relaxation times were obtained by means of a regularized numerical inversion of experimental static magnetization and dynamic susceptibility curves. These distributions contain full information about the microstructure of ferrofluids. Analysis of the distribution curves showed the temperature-dependent evolution of the ferrofluid microstructure in the zero applied magnetic field: particle aggregates form or disintegrate and magnetic moment relaxation mechanism changes depending on the temperature.

Effects of Different Fatty Acids as Surfactants on the Rheological Properties of Kerosene-Based Magnetic Fluids

Three types of surfactants (oleic acid, linoleic acid, and a mixture of oleic acid and linoleic acid) were coated on ferromagnetic particles, which were dispersed in kerosene to prepare magnetic fluids, to study the effect of different fatty acids as surfactants on the rheological properties of magnetic fluids. The particles were analyzed by XRD, TEM, FT-IR, and VSM. Furthermore, a rheometer was used to examine the rheological properties of kerosene-based magnetic fluids dispersed with various surfactants. The yield stress at different magnetic fields was calculated by fitting the Herschel–Bulkley model. The fitted curve and the observed values of mixed fatty acids are identical. The graphs of viscosity increase with the shear rate for each magnetic fluid were measured at constant magnetic field strengths. At constant shear rates, the curves of viscosity increase with magnetic field intensity were measured. In the absence of a magnetic field, the relative change in viscosity from 40°C to 0°C was observed. The rheological measurements of the mixed fatty acid-dispersed ferrofluid with a rising magnetic field at a constant shear rate are smoother than the single-fatty-acid-dispersed ferrofluid, indicating that it is more stable. As the temperature is dropped, the viscosity–temperature curve evidence that mixed fatty acids as surfactants can lower the proportion of magnetic fluid viscosity rise.

Analysis of processes in magnetorheological sealer considering for magnetic fluid deformation

The small size of the working gap in the sealer makes many physical measurements difficult or impossible. The main way to study the processes inside the device is to use analytical and numerical mathematical modeling. Most researchers apply finite-element calculation of magnetic field and analytically find the difference in pressure. Currently, there are few studies devoted to multiphysics numerical calculations of the processes in magnetorheological seal. The use of numerical models allows considering the dependence of rheological properties of magnetic fluid on hydrodynamic, temperature and magnetic fields, the real geometry of the working zone. Compared to the analytical models, a numerical one includes a smaller number of assumptions and allows visualizing various flow parameters, which are especially important for the analysis. The purpose of this study is to analyze the effect of the deformation of the magnetorheological plug in case of pressure difference held by the sealer. The study is based on the developed numerical model with the related calculation of magnetic and hydrodynamic fields. The study is carried out based on the theories of ferrohydrodynamics, hydrodynamics and electromagnetic field. Integrated finite-element modeling of the magnetic and hydrodynamic fields of the magnetorheological sealer in Comsol Мultiphysics has been used. A numerical model of the magnetorheological sealer characterized by automatic rearrangement of the boundaries of the liquid plug based on the balance of pressures inside the liquid has been developed. The distribution results of magnetic induction and pressure in the working gap of the sealer, considering changes in the boundaries of the magnetic fluid, has been obtained. Comparison of the results of the obtained retained pressure drop and the results of other models has been carried out. A numerical mathematical model that considers the deformation of the magnetorheological plug has been developed. The model makes it possible to estimate the influence of centrifugal forces of the rotating shaft on the retained pressure drop. The results can be used to create high-speed seal components. The difference of the value of analytical calculation does not exceed 5 %. The assumption about full filling of the working gap with magnetic fluid 2,5 times underestimates the retained pressure difference at high shaft rotation speeds.

Elastic Properties of Magnetic Fluids

Elastic Properties of Magnetic Fluids

Experimental Study on the Leak Mechanism of the Ferrofluid Seal in a Water Environment

The advantages of magnetic fluid seals, such as low friction moment, high tightness, and high durability, have been known for many years. However, they are used particularly in air or vacuum environments and the application of this type of seal in water still remains a problem. This is mainly due to the friction occurring between the two fluids and interfacial instability. This publication focuses on investigating the influence of magnetic fluid properties on the mechanism of pressure transfer between sealing stages. The main aim was to better understand the leak mechanism in this type of seal and to be able to select ferrofluids (FFs) resistant to water for long-term operation after short-term testing. The tested seals rotated over 4.3 million times without failure. The results of the research carried out are recommendations for the selection of magnetic fluid, sealing stage width, and FF volume.

Reconfiguring nanostructures in magnetic fluids using pH and magnetic stimulus for tuning optical properties

In this paper, we demonstrate tuning the optical properties of magnetic fluids through pH and magnetic field control. The role of reconfigurable nanostructures in the temporal and switching behavior of transmitted light is also studied. An oil-in-water magnetic nanoemulsion with an average diameter of 200 nm, containing Fe3O4 superparamagnetic nanoparticles of 10 nm average diameter, is used in this study. To make the emulsion pH reconfigurable, the droplets are covered with a weak polyelectrolyte, poly (acrylic acid). The swelling of the PAA molecules, due to ionization of the carboxylic acid groups, resulted in an increase in adlayer thickness at increase in pH. The change in transmitted intensity is found to scale linearly with the applied magnetic field strength, and at higher fields, the formed structures took more time to reconfigure themselves after the removal of magnetic field. At a pH 5, the increase in transmitted light intensity is seen even at a very low magnetic field strength due to the lower interdroplet spacing. On the contrary, at pH 9, the interdroplet spacing between the emulsion drops were large, due to the extension of PAA molecules, which led to a weaker magnetic interaction between the droplets and formation of shorter chains, where a lower transmission is seen due to multiple scattering. A straight-line pattern was observed in the transmitted intensity, due to the scattering of light from linear chains that are aligned perpendicular to the light propagation direction. Bridging of polymer covered surfaces was seen at pH 3, due to hydrogen bonding between PAA molecules. Our results show that tuning optical properties of magnetic emulsion (switching between transparent and opaque states) is possible through pH control. Our findings open up new opportunities to develop optical devices and accessing of diverse structures by tuning pH and magnetic field.

Theoretical comparison of rheological properties of high-viscosity municipal sludge and magnetic liquid

The composition and structure of sludge determine its complex rheological properties. When the shear stress is small, the deformation of the structural skeleton appears elastic. As the shear stress increases, the structural skeleton begins to break until it is completely destroyed. In this process, it shows viscoelasticity, and its viscosity gradually dominates. A part of the basic fluid flows out from the damaged structural skeleton, causing the sludge to change from deformation to flow, the shear stress at which it starts to flow is called the yield stress. After the flow, the viscosity decreases with the increase of the shear rate, which is called the shear thinning characteristic. Magnetic fluid is a new type of magnetically sensitive smart material. In the past fifty years, a large number of results have been achieved in the research on the rheological properties of magnetic fluids. However, due to the extremely complex anisotropic structure formed inside the magnetic fluid under a magnetic field. At the same time, the macro-rheological experiment lacks systemicity, and it is urgent to integrate the research results obtained by different experimental methods. Even in the field of the most fully studied magnetic viscosity effect, based on strong idealization assumptions the chain-micro-model is widely used, it cannot be used to analyze the results of macroscopic rheological experiments.