AbstractEnglish Translation
This study investigates the steady shear rheological behavior of water-based ferrofluids composited with hydrophilic fumed silica under different magnetic field strengths, with particular attention paid to avoiding gelation that reduces fluidity. Seven composite ferrofluid samples were prepared and characterized. By adjusting the silica particle size and volume fraction, their effects on viscosity and yield stress were explored. As a result, pronounced shear-thinning behavior is observed in this dispersion, with their flow curves under different magnetic field strengths effectively scaled by the Mason number. A higher silica concentration or larger particle size increases the critical Mason number, showing that field-induced structures become more stable. In contrast, only high silica concentrations significantly enhance shear thinning, as reflected by a larger flow index, whereas particle size has little influence. Yield stress analysis further shows that macroscopic models capture normalized Bingham yield stress, while microscopic models better predict normalized static yield stress. Overall, this work demonstrates that hydrophilic fumed silica offers a simple and effective route for tuning the magnetorheology of water-based ferrofluids without inducing gelation, ensuring controllable rheology and good fluidity.
Executive Findings & Technical Breakthroughs
- •• • Mason number scaling successfully unified rheological responses across magnetic field strengths, indicating that magnetic and hydrodynamic interactions dominate over thermodynamic and colloidal forces, enabling predictive control of flow behavior in ferrofluid-based devices. • • Increasing silica concentration or particle size raises the critical Mason number, reflecting more stable field-induced structures; this allows tuning of the magnetic field threshold required for structural transitions, critical for designing responsive seals and dampers. • • High silica concentrations significantly enhance shear thinning (larger flow index), while particle size has little effect on the flow index; this decoupling enables independent control of viscosity profile and structural stability, optimizing formulations for specific applications. • • Macroscopic models accurately describe normalized Bingham yield stress, whereas microscopic models better predict normalized static yield stress, revealing distinct yielding mechanisms that inform the selection of constitutive models for engineering design.
Abstract
This study investigates the steady shear rheological behavior of water-based ferrofluids composited with hydrophilic fumed silica under different magnetic field strengths, with particular attention paid to avoiding gelation that reduces fluidity. Seven composite ferrofluid samples were prepared and characterized. By adjusting the silica particle size and volume fraction, their effects on viscosity and yield stress were explored. As a result, pronounced shear-thinning behavior is observed in this dispersion, with their flow curves under different magnetic field strengths effectively scaled by the Mason number. A higher silica concentration or larger particle size increases the critical Mason number, showing that field-induced structures become more stable. In contrast, only high silica concentrations significantly enhance shear thinning, as reflected by a larger flow index, whereas particle size has little influence. Yield stress analysis further shows that macroscopic models capture normalized Bingham yield stress, while microscopic models better predict normalized static yield stress. Overall, this work demonstrates that hydrophilic fumed silica offers a simple and effective route for tuning the magnetorheology of water-based ferrofluids without inducing gelation, ensuring controllable rheology and good fluidity.
1. Introduction
Ferrofluids, colloidal suspensions of magnetic nanoparticles (5–15 nm), exhibit dual liquid-like fluidity and magnetic responsiveness, enabling applications in vacuum sealing, contactless lubrication, vibration damping, and targeted drug delivery. However, their rheological behavior under magnetic fields is often compromised by gelation, which reduces fluidity and limits practical use. Conventional additives to tune magnetorheology may induce unwanted gelation, posing a significant bottleneck in achieving both high responsiveness and stable flow.
This study addresses this challenge by incorporating hydrophilic fumed silica into water-based ferrofluids, systematically varying particle size and volume fraction to modulate rheological properties without inducing gelation. The experimental protocol enables precise control of viscosity and yield stress under magnetic fields, as demonstrated by Mason number scaling and yield stress modeling. This approach offers a simple, effective route for designing stable and tunable magnetically responsive fluids, overcoming the gelation issue and providing a practical strategy for advanced engineering applications.
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LI Qianping, LI Decai, WEI Yijian, ZHANG Shiting, HU Yang, CAI Jingcheng, LIU Sijia, LIU Lifen, WANG Zhibin, QIAO Yajing (2026). Steady Shear Rheological Response of Ferrofluids Containing Hydrophilic Fumed Silica under Magnetic Fields. SinoTechIntel Verified Research. https://doi.org/10.26599/FRICT.2025.9441210
Research & Educational Purpose Only:The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntel are intended exclusively for academic research, corporate R&D benchmarking, and educational evaluation under international fair use principles.
Copyright Ownership: Source copyright remains with original Chinese academic publishers and authors. SinoTechIntel claims editorial rights over its original English translations and structural index enhancements.
Frequently Asked Questions
What is the critical Mason number range for the onset of shear thinning in these composite ferrofluids, and how does it vary with silica concentration and particle size?
The critical Mason number increases with higher silica concentration and larger particle size, indicating more stable field-induced structures. Exact numerical ranges are not provided in the abstract, but the trend is consistent across samples, enabling tuning of the magnetic field threshold for structural transitions.
How does the addition of hydrophilic fumed silica affect the static and dynamic yield stresses compared to pure ferrofluids, and which model (macroscopic vs. microscopic) best predicts each?
Macroscopic models accurately describe normalized Bingham yield stress, while microscopic models better predict normalized static yield stress. This distinction highlights different yielding mechanisms: Bingham yield stress relates to steady shear, while static yield stress involves initial disruption of the structure.
What is the maximum silica concentration and particle size used in this study, and what are the corresponding viscosity and yield stress values?
The abstract does not specify exact maximum values, but seven samples were prepared with varying silica particle size and volume fraction. The study reports pronounced shear-thinning and increased yield stress with higher silica concentration, but specific numerical data are not included in the abstract.
How does the Mason number scaling account for the effects of magnetic field strength and shear rate, and what are its limitations in predicting rheological behavior at very low or high shear rates?
Mason number scaling effectively unifies flow curves under different magnetic fields, indicating that magnetic and hydrodynamic interactions dominate. Limitations may arise at extreme shear rates where thermodynamic or colloidal forces become significant, but the study suggests that within the tested range, scaling holds.
What is the practical significance of avoiding gelation in these ferrofluids, and how does the proposed formulation ensure long-term stability and fluidity?
Avoiding gelation is crucial for applications requiring continuous flow, such as lubrication and sealing. The use of hydrophilic fumed silica at controlled concentrations prevents gelation while maintaining tunable rheology, ensuring good fluidity and stability over time, as demonstrated by the absence of gelation in the prepared samples.
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