Enhancing Electrorheological Fluid Performance through Barium Titanate@Nanocarbon Shell Composites

Electrorheological (ER) fluids exhibit dramatic changes in their mechanical and rheological properties when exposed to an electric field. These smart fluids, often consisting of a suspension of polarizable particles in a non-conducting fluid, can swiftly transition from a liquid-like state to a solid-like state upon the application of an electric field. This unique property makes ER fluids highly valuable in a variety of applications where controlled motion and force are required.  However, challenges remain in the widespread adoption of ER fluids. The stability of the suspension, particle sedimentation, and the high electric fields required to achieve significant changes in viscosity are some of the issues that need addressing.  To this account, a new study published in the ACS Applied Materials and Interfaces and conducted by Miss. Sai Chen, Professor Yuchuan Cheng, Mr. Zihui Zhao, Dr. Ke Zhang, Dr. Tingting Hao, Professor Yi Sui, Professor Wen Wang, Professor Jiupeng Zhao, and Professor Yao Li from the Harbin Institute of Technology, Chinese Academy of Sciences, Queen Mary University of London, researchers investigated the significant impact of nanocarbon-based materials on ER fluids. They synthesized and analyzed the ER behavior of barium titanate@nanocarbon shell (BTO@NCs) composites, incorporating carbonized polydopamine (C-PDA) into the shell.

The team synthesized BTO@NCs composites using a two-step process. First, BTO nanoparticles were coated with PDA by stirring BTO nanoparticles in a Tris-HCl buffer solution, to which dopamine hydrochloride was added. The mixture’s pH was adjusted to 8.5 using sodium hydroxide, and the reaction was allowed to proceed for varying durations (12, 24, and 48 hours) to control the thickness of the PDA coating. These PDA-coated nanoparticles were then carbonized at 500 °C under an inert atmosphere to form the nanocarbon shell, resulting in BTO@NCs composites with different shell characteristics. Afterward, the synthesized BTO@NCs nanoparticles were dispersed in silicone oil to create ER fluids. The concentration of nanoparticles and the preparation method (mechanical stirring and ultrasonication) were carefully controlled to ensure a homogeneous dispersion of nanoparticles within the silicone oil, forming the basis for subsequent ER behavior testing.

The authors performed comprehensive material characterization to analyze the morphology, structure, and composition of the synthesized BTO@NCs nanoparticles and the ER fluids and used transmission electron microscopy and high-resolution TEM to visualize the morphology and nanostructure of the BTO@NCs, revealing the core-shell structure and the variation in shell thickness. They also used x-ray diffraction to confirm the crystalline structure of BTO within the composites, which indicated that the carbonization process did not alter the BTO’s crystal structure, X-ray photoelectron spectroscopy to provide information on the surface chemistry, which showed variations in the sp²/sp³ carbon ratio and the presence of surface functional groups, which are important for the ER response and they used Fourier transform infrared spectroscopy to identify the specific functional groups present on the nanocomposite’s surface, which provided additional confirmation for the presence of polar groups that facilitate ER behavior and Raman Spectroscopy was employed to analyze the degree of graphitization, with changes in the I_D/I_G ratio indicating how the polymerization time influenced the carbon structure.

The research team also evaluated the ER performance of the fluids, where they measured the relationship between shear stress and shear rate under varying electric fields, revealing how the ER fluids transitioned from a liquid to a solid-like state using flow curve analysis. Dielectric Measurements assessed the dielectric properties of the ER fluids, important for understanding the polarization behavior under an electric field and rheological measurements were used to quantify the yield stress and viscosity of the ER fluids, indicating the strength of the ER effect under different conditions. The authors found that the optimal polymerization time to be 24 hours, producing BTO@NCs with the best combination of shell thickness, sp²/sp³ carbon ratio, and surface functional groups, leading to the highest ER response. Moreover, the ER fluid containing BTO@NCs synthesized with 24 hours of polymerization exhibited a maximum yield stress of 2.5 kPa at an electric field strength of 4 kV/mm, significantly higher than that of BTO@NCs synthesized with shorter or longer polymerization times. Furthermore, the increased content of sp³ C-OH and oxygen-containing functional groups within the shell was attributed to the enhanced ER response, indicating that these groups play a crucial role in achieving rapid polarization and strong ER effects. Additionally, comparative analysis with SiO₂@NCs and TiO₂@NCs ER fluids also prepared showed enhanced ER behavior, confirming the effectiveness of the approach for high-performance ER fluids based on nanocarbon composites.

The novelty of this study lies in its approach to manipulating the carbon structure of C-PDA to optimize ER response, highlighting the importance of sp²/sp³ -hybridized carbon structures and the role of surface polar functional groups in achieving rapid polarization. The control over polymerization time allowed for the fine-tuning of shell thickness and the functional group density on the nanocarbon shell, which in turn influences the ER fluid’s properties. This level of control is important for the development of smart materials that can respond predictably to external stimuli. In conclusion, the work of Harbin Institute of Technology scientists exemplifies the cutting-edge research in nanomaterials and their applications in creating functional and adaptive materials.  The study conducted on the development of BTO@NCs composites for use in ER fluids carries substantial significance across multiple domains of materials science, engineering, and applied physics.   ER fluids with enhanced properties as demonstrated in this study can be used in a wide range of applications, from automotive systems (such as adaptive suspensions and clutches) to haptic feedback devices in virtual reality systems and soft robotics. Improved ER fluids could lead to more efficient, responsive, and durable systems. There is potential for these advanced ER fluids to be used in the development of novel medical devices, such as artificial muscles or other devices that require precise control of movement and stiffness. This could lead to innovations in prosthetics, orthotics, and other assistive technologies. Moreover, improved ER fluids can lead to more energy-efficient systems in automotive and industrial applications, potentially reducing energy consumption and environmental impact.