A Study on the Surface Finishing Technique using Electrorheological Fluid

Sung-Jun Park,Wook-Bae Kim,Sang-Jo Lee 한국정밀공학회 2004 International Journal of Precision Engineering and Vol.5 No.2

The electrorheological(ER) fluid has been used to the ultraprecision polishing of single crystal silicon as new polishing slurry whose properties such as yield stress and particle structure changed with the application of an electric field. In this work, it is aimed to find the effective parameters in the ER fluid on material removal in the polishing system whose structure is similar to that of the simple hydrodynamic bearing. The generated pressure in the gap between a moving wall and a workpiece, as well as the electric field-induced stress of the mixture of ER fluid-abrasives, is evaluated experimentally, and their influence on the polishing of single crystal silicon is analyzed. Moreover, the behavior of abrasive and ER particles is described.

Fabrication of density-controlled graphene oxide-coated mesoporous silica spheres and their electrorheological activity

Yoon, Chang-Min,Lee, Seungae,Hong, Seung Hee,Jang, Jyongsik Elsevier 2015 JOURNAL OF COLLOID AND INTERFACE SCIENCE - Vol.438 No.-

<P><B>Abstract</B></P> <P>A series of density-controlled graphene oxide-coated mesoporous silica spheres (GO/SiO<SUB>2</SUB>) are successfully synthesized to investigate the influence of the particle density on electrorheological (ER) activity. The particle density of mesoporous silica spheres is controlled by creating different sized pores <I>via</I> surfactant template and swelling agent incorporation method. Additionally, ball-milled graphene oxide is successfully coated onto the surface of various silica spheres (SiO<SUB>2</SUB>) through amine-modification to enhance ER efficiency. In this study, we investigate that mesoporous silica spheres-based ER fluid (GO/epSiO<SUB>2</SUB>) with lowest particle density exhibit most increased ER performance, which is 3-fold higher than that of similar sized neat silica spheres-based ER fluid (GO/nSiO<SUB>2</SUB>) without pore. In addition, the relationship between particle density, anti-sedimentation property, and ER performance is examined by applying Stokes’ law and practical sedimentation observation. Furthermore, dielectric loss model is used to clarify the influence of dielectric property on ER activity. This newly designed ER study offers insight into the influence of the particle density on the performance of ER fluids.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Series of density-controlled graphene oxide-coated silica spheres were synthesized. </LI> <LI> It is first attempt to investigate the effect of particle density on electrorheological activity. </LI> <LI> Electrorheological performance was enhanced with decreasing particle density. </LI> <LI> Shear stress inversion phenomenon was specified in the fluctuating region for first time. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

A Study on the Surface Finishing Technique using Electrorheological Fluid

Park, Sung-Jun,Kim, Wook-Bae,Lee, Sang-Jo Korean Society for Precision Engineering 2004 International Journal of Precision Engineering and Vol.5 No.2

The electrorheological(ER) fluid has been used to the ultraprecision polishing of single crystal silicon as new polishing slurry whose properties such as yield stress and particle structure changed with the application of an electric field. In this work, it is aimed to find the effective parameters in the ER fluid on material removal in the polishing system whose structure is similar to that of the simple hydrodynamic bearing. The generated pressure in the gap between a moving wall and a workpiece, as well as the electric field-induced stress of the mixture of ER fluid-abrasives, is evaluated experimentally, and their influence on the polishing of single crystal silicon is analyzed. Moreover, the behavior of abrasive and ER particles is described.

Enhanced Electrorheological Performance of Mixed Silica Nanomaterial Geometry

Yoon, Chang-Min,Jang, Yoonsun,Noh, Jungchul,Kim, Jungwon,Lee, Kisu,Jang, Jyongsik American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.41

<P>The mixed geometrical effect on the electror-heological (ER) activity of bimodal ER fluids was investigated by mixing SiO2 spheres and rods of different dimensions. To, gain an in-depth understanding of the mixed geometrical effect, 12 bimodal ER fluids were prepared from 4 sizes of SiO2 spheres (50, 100, 150, and 350 nm) and 3 types of SiO2 rods with different aspect ratios (LID = 2, 3, and 5). Five concentrations of SiO2 spheres and rods were created for each bimodal ER fluid, resulting in a total of 60 sets of comprehensive ER measurements. Some bimodal ER fluids exhibited enhanced ER performance, as high as 23.0%, compared to single SiO2 rod-based ER fluids to reveal the mixed geometrical effect of bimodal ER fluids. This interesting experimental result is based on the structural reinforcement provided by spheres to fibrillated rod materials, demonstrating the mixed geometrical effect on ER activity.</P>

Electrorheological Properties of Polypyrrole and its Composite ER Fluids

김영대,김도형 한국공업화학회 2007 Journal of Industrial and Engineering Chemistry Vol.13 No.6

Electrorheological (ER) fluids are suspensions of polarizable nonconducting or semiconducting particles in a nonconducting continuous phase of low relative polarizability. In the absence of an electric field, they have the properties of suspensions of neutral solid particles. Upon the application of an electric field, an organized structure of particles is formed and the ER fluids exhibit a remarkable change in rheological properties, including a drastic increase in apparent viscosity as well as yield stress. Various mechanisms have been proposed to explain the ER behavior to understand the ER behaviors and design effective ER fluids. Polypyrrole (PPy) is one of the most promising semiconducting polymers because it has higher conductivity and environmental stability than many other semiconducting polymers. PPy and its composites have been extensively used as ER materials and their ER fluids showed promising ER responses. ER properties of PPy based ER fluids (PPy, PPy copolymer, PPy coated particles, and PPy nanocomposites, etc.) and the ER behaviors of PPy based ER fluids such as shear, yield, and transient stress behavior and additive effect are reviewed.

전기유변 유체의 압착유동에 대한 동적 수치모사

김도훈,주상현,안경현,이승종 한국유변학회 1999 Korea-Australia rheology journal Vol.11 No.2

Electrorheological(ER) fluid is a material that shows the dramatic change of rheological properties under an electric field and responds reversibly in a few milliseconds. ER fluid's response to an electric field along with its fast switching capability allows ER devices to be precisely controlled. The real application with ER fluid, however, has many limitations to be overcome; temperature fluctuation, moisture, dust, aggregation, precipitation, and low yield stress, for example. The magnitude and the characteristics of yield stress of ER fluid plays an important role in practical applications. In this research, a dynamic simulation on the squeezing flow of the ER fluid was carried out. Numerical simulation on isolated chains was performed to find out the effect of hydrodynamic and electrostatic force depending on the chain location, the squeezing rate, and the chain structure. Suspension model that is composed of a large number of particles was also investigated. The increase of normal stresses as well as the existence of a yield stress at an earlier stage could be observed, and the effective control of the normal stresses could be achieved at an optimal condition of the hydrodynamic force and the electrostatic force. 전기유변 유체(electorheological fluid)는 전기장이 가해지면 아주 짧은 시간에 유변 물성이 급격히 변하며 그 응답이 반복적으로 수행될 수 있는 유체이다. 전기유변 유체는 전기장의 세기에 따라 면찰 응력(shear stress)과 점도의 크기를 조절할 수 있고, 짧은 응답시간은 빠른 제어를 요하는 분야에 효과적으로 이용될 수 있지만, 낮은 항복 응력, 조업 온도 범위의 제한성, 전력 소비에 의한 열적 불안정성, 그 외에도 응집, 침전 등의 단점이 있다. 특히, 이 유체가 갖는 항복 응력의 크기와 그 성질은 실제 장치에 응용하는데 중요한 특성이다. 이러한 문제점을 해결하기 위해 면찰 유동(shear flow)이 아닌 압착 유동(squeezing flow)을 고려하게 되었고, 이 유동 하에서의 전기유변 유체의 거동을 이해하기 위해 본 연구에서는 전기유변 유체의 압착 유동에 대한 동적 수치모사를 수행하였다. 고립된 사슬 구조에 대한 수치모사를 통하여 사슬의 위치와 압착 속도를 변화 시키면서 이에 따른 수력학적 힘과 정전기적 힘의 효과를 예측하였으며, 이를 토대로 많은 사슬을 포함한 현탁액 모델에 대한 수치모사를 수행하였다. 그 결과 실험에서 관찰할 수 있는 수직 응력의 증가와 초기 항복 응력의 존재를 확인하였고, 수직 응력의 효과적인 제어는 수력학적 힘과 정전기적 힘 간의 최적화된 조건에서 얻어질 수 있음을 예측하였다. 이러한 수치모사의 개발을 통해 압착 유동을 이용한 전기유변 유체의 응용에 대한 이론적인 토대를 마련하였고, 향후 보다 깊은 이해를 위한 기반을 구축할 수 있었다.

인산화 전분 ER 유체의 트라이볼로지 특성

장민규(Min-Gyu Jang),이철희(Chul-Hee Lee),최재영(Jea-Young Choi),손정우(Jung Woo Sohn),최승복(Seung-Bok Choi) 한국트라이볼로지학회 2010 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.26 No.1

This experimental study presents tribological characteristics under boundary lubrication contacts associated with electrorheolocal (ER) fluid. ER fluid is prepared by using phosphorated starch particles and silicone oil. Experimental apparatus of tribological tester is designed and constructed to evaluate tribological characteristics of pin specimens. Wear tests under boundary lubrication of ER fluid are experimentally performed under consideration of several operational factors such as normal load, sliding distance, sliding speed and specimen materials: steel, copper and aluminum. After wear test, microscopic surface changes of the worn pin specimens are analyzed in order to investigate measured wear characteristics by using the scanning electron microscope (SEM) as well as surface profilometer. In addition, the chemical wear characteristics are investigated by using energy dispersive x-ray spectroscopy (EDS). Moreover, friction coefficient measurements under different materials of pin specimens are conducted for the tribological investigations. In order to verify the effect of starch phosphate particles in ER fluid, the wear test results with ER fluid are compared with test results with only silicone oil. The results clearly present that the phosphorated starch based ER fluid shows the stabilized wear as well as friction characteristics after run-in operations, but the wear rate under ER fluid is increased.

Synthesis and electrorheological characteristics of titanate nanotube suspensions under oscillatory shear

Ying He,Chunzhong Li,Qilin Cheng,Petr Saha,Vladimir Pavlinek 한국공업화학회 2009 Journal of Industrial and Engineering Chemistry Vol.15 No.4

In this study, titanate nanotubes (TNTs) were synthesized by hydrothermal treatment of TiO2 powders (P25) in a NaOH solution. The as-synthesized TNTs exhibit high surface area and large aspect ratio. Rheological properties of TNTs suspensions were then investigated under oscillatory shear. The TNTs fluid shows the viscoelastic behavior and the dynamic moduli (G0, G00) increase significantly by about 4 orders ofmagnitude as the electric field strength is up to 2.0 kV/mm. Transient response under dynamic shear reveals different changes in the microstructure of TNTs fluid from steady shear. The complex modulus of TNTs fluids is sensitive to temperature while that of P25 fluid become insensitive at higher temperature. Dynamic viscoelastic behavior suggests that structure of P25 to TNTs transition merits the enhancement of ER activity of TNTs fluid.

Characterization and electrorheological response of silica/titania-coated MWNTs synthesized by sol-gel process

Oh, S.Y.,Oh, M.K.,Kang, T.J. Elsevier 2013 Colloids and surfaces. A, Physicochemical and engi Vol.436 No.-

Silica or titania uniformly coated multi-walled carbon nanotubes (MWNTs) were fabricated using the tetraethyl orthosilicate (TEOS) or titanium butoxide (TBT) for the application of electrorheological (ER) fluids. The electrorheological and dielectric properties of the two different core/shell nano-tube based ER fluids were measured using rheometer and impedance analyzer. The titania-coated MWNTs ER fluids have shown higher static yield stress as well as dynamic viscoelastic properties compared to the silica-coated MWNTs ER fluids under external electric field. The silica or titania-coated MWNTs ER fluids have shown high permittivity and short relaxation time of interfacial polarization in the dielectric spectra measurement. It was found that the permittivity and electrical conductivity of the MWNTs can be controlled by coating with either the silica or titania onto the functionalized MWNTs.

인산화 전분 ER 유체의 트라이볼로지 특성

장민규(Min-Gyu Jang),최재영(Jae-Young Choi),이철희(Chul-Hee Lee),손정우(Jung-Woo Sohn),최승복(Seung-Bok Choi) 한국트라이볼로지학회 2009 한국트라이볼로지학회 학술대회 Vol.2009 No.6

This experimental study presents tribological characteristics under boundary lubrication contacts associated with electrorheolocal(ER) fluid. ER fluid is prepared by using phosphorated starch particles and silicone oil. Experimental apparatus of tribological tester is designed and constructed to evaluate tribological characteristics of pin specimens. Wear tests under boundary lubrication of ER fluid are experimentally performed under consideration of several operational factors such as normal load, sliding distance, sliding speed and specimen materials: steel, copper and aluminum. After wear test, microscopic surface changes of the worn pin specimens are analyzed in order to investigate measured wear characteristics by using the scanning electron microscope (SEM) as well as surface profilometer. Moreover, friction coefficient measurements under different materials of pin specimens are conducted for the tribological investigations. In order to verify the effect of starch phosphate particles in ER fluid, the wear test results with ER fluid are compared with test results with only silicone oil. The results clearly present that the phosphorated starch based ER fluid shows the stabilized wear as well as friction characteristics after run-in operations, but the wear rate under ER fluid is increased.