Siti Aishah Abdul Aziz

Effects of multiwall carbon nanotubes on viscoelastic properties of magnetorheological elastomers

The effect of different types of multiwall carbon nanotubes (MWCNTs) on the morphological, magnetic and viscoelastic properties of magnetorheological elastomers (MREs) are studied in this work. A series of natural rubber MRE are prepared by adding MWCNTs as a new additive in MRE. Effects of functionalized MWCNT namely carboxylated MWCNT (COOH-MWCNT) and hydroxylated MWCNT (OH-MWCNT) on the rheological properties of MREs are investigated and the pristine MWCNTs is referred as a control. Epoxidised palm oil (EPO) is used as a medium to disperse carbonyl iron particle (CIP) and sonicate the MWCNTs. Morphological and magnetic properties of MREs are characterized by field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM), respectively. Rheological properties under different magnetic field are evaluated by using parallel plate rheometer. From the results obtained, FESEM images indicate that COOH-MWCNT and CIP have better compatibility which leads to the formation of interconnected network in the matrix. In addition, by adding functionalized COOH-MWCNT, it is shown that the saturation magnetization is 5% higher than the pristine MWCNTs. It is also found that with the addition of COOH-MWCNT, the magnetic properties are improved parallel with enhancement of MR effect particularly at low strain amplitude. It is finally shown that the use of EPO also can contribute to the enhancement of MR performance.

Rheological properties of isotropic magnetorheological elastomers featuring an epoxidized natural rubber

This study presents principal field-dependent rheological properties of magnetorheological elastomers (MREs) in which an epoxidized natural rubber (ENR) is adopted as a matrix (in short, we call it ENR-based MREs). The isotropic ENR-based MRE samples are fabricated by mixing the ENR compound with carbonyl iron particles (CIPs) with different weight percentages. The morphological properties of the samples are firstly analysed using the microstructure assessment. The influences of the magnetic field on the viscoelastic properties of ENR-based MREs are then examined through the dynamic test under various excitation frequencies. The microstructure of MRE samples exhibits a homogeneous distribution of CIPs in the ENR matrix. The dramatic increment of storage modulus, loss modulus and loss tangent of the ENR-based MREs are also observed from the field-dependent rheological test. This directly demonstrates that the stiffness and damping properties of the samples can be adjusted by the magnetic field. It is also seen that the CIP content, exciting frequency and the magnetic field essentially influence the dynamic properties of the ENR-based MREs. The strong correlation between the magnetization and the magneto-induced storage modulus could be used as a useful guidance in synthesizing the ENR-based MREs for certain applications.

The field-dependent complex modulus of magnetorheological elastomers consisting of sucrose acetate isobutyrate ester

In this work, epoxidized natural rubber-50 magnetorheological elastomer was synthesized using conventional rubber processing. The ester plasticizer sucrose acetate isobutyrate was then incorporated into epoxidized natural rubber-50 to soften the matrix and to improve the relative magnetorheological effect. The influence of sucrose acetate isobutyrate ester on the microstructures and properties of epoxidized natural rubber-50 magnetorheological elastomers were experimentally investigated. It has been identified that the addition of sucrose acetate isobutyrate ester can reduce the viscosity of the matrix and increase the mobility of magnetic particles in a matrix. The elongation of magnetorheological elastomer was increased by 19%, and the tensile strength was reduced by 17% at 10 wt% content of the sucrose acetate isobutyrate ester. It is observed that the employment of sucrose acetate isobutyrate ester enhanced the thermal stability leading to low degradation of the properties of magnetorheological elastomer. In rheology test, both absolute and relative magnetorheological effects were increased by 0.16 MPa and 23%, respectively, with incorporation of the 7.5-wt% sucrose acetate isobutyrate ester. It is also identified that the storage and loss moduli as well as loss factor are increased as the excitation frequency is increased. It is finally concluded that agglomeration issues in isotropic magnetorheological elastomer which degrade performances of magnetorheological elastomer application devices and systems can be resolved by the addition of sucrose acetate isobutyrate ester to epoxidized natural rubber-50 used in this work.

An enhancement of mechanical and rheological properties of magnetorheological elastomer with multiwall carbon nanotubes

In this work, a new type of magnetorheological elastomer, which is reinforced by carbon nanotubes, is fabricated and its material properties are experimentally investigated. In order to achieve this goal, as a first step, different types of multiwall carbon nanotubes are incorporated into a series of natural rubber–based magnetorheological elastomers as additives. Several experimental instruments such as X-ray diffractometer, thermogravimetric analysis, and differential scanning calorimetry are utilized. From the test, several salient properties of the proposed magnetorheological elastomer are observed or/and characterized. The results indicate that the interaction between natural rubber–based magnetorheological elastomers and multiwall carbon nanotubes can provide significant improvement in mechanical and rheological properties. More specifically, it is observed that mechanical properties such as tensile strength are enhanced up to 11% by the functionalized multiwall carbon nanotube. It is also found that the field-dependent storage and loss moduli of the proposed magnetorheological elastomer samples are increased compared to magnetorheological elastomer without multiwall carbon nanotube. It is finally identified that magnetorheological efficiency, which indicates force controllability by the magnetic field, of the proposed magnetorheological elastomer samples is consistent with the increased operating frequency. Therefore, it is expected that the results of morphological, thermal, and rheological properties parallel to incorporation of multiwall carbon nanotubes into magnetorheological elastomers are effectively used for proper selection of magnetorheological elastomer applications.

An overview of nanoparticles utilization in magnetorheological materials

Magnetorheological (MR) materials belong to smart materials family where the rheological properties can be altered continuously, rapidly and reversibly through the external magnetic field. The tuneable properties depend on the magnitude of the external magnetic field. The micron-sized magnetizable particles having high saturation magnetization within matrix carrier react to the magnetic field resulting in alteration of MR effect. The classic problem of smart materials is particles sedimentation and aggregation issues due to the high concentration and large size of magnetic particles. Many researchers have attempted to solve this issues by introducing nano-sized particles into these materials. Based on the previous researches, the nanoparticles incorporation in MR materials is reported to improve the stability of the MR materials and at the same time enhance the MR performance. This paper presents an overview of nanoparticles incorporation in different types of MR materials which are MR fluids, MR grease, and MR elastomer including the stability and performance achievement regarding rheological properties.

Investigation on magnetic field dependent modulus of epoxidized natural rubber based magnetorheological elastomer

This paper presents an investigation on the use of epoxidized natural rubber (ENR) as a matrix of magnetorheological elastomers (MREs). Isotropic ENR-based MRE samples were synthesized by homogeneously mixed the ENR compound with carbonyl iron particles (CIPs). The microstructure of the sample was observed, and the magnetic field-dependent moduli were analyzed using rheometer. The influences of excitation frequency, CIPs content and magnetic field on the field-dependent moduli of ENR-based MREs were evaluated through dynamic shear test. The microstructure of MRE samples demonstrated the dispersed CIPs in the ENR matrix. The remarkable increment of storage and loss moduli of the ENR-based MREs has exhibited the magnetically controllable storage and loss moduli of the samples when exposed to the magnetic field. Consequently, the CIPs content, frequency and magnetic field were significantly influenced the dynamic moduli of the ENR-based MREs.

Performance of Magnetorheological Elastomer Based Silicone/SAIB

This study introduces a sucrose acetate isobutyrate (SAIB) as an additive of magnetorheological elastomers (MREs) to be added in silicone rubber matrix and carbonyl iron particles (CIPs) as their filler. The CIPs were fixed at 60 wt% and two types of MREs sample were fabricated which are isotropic and anisotropic. Rheological properties related to shear storage modulus were measured using a rheometer (MCR 302, Anton Paar). The experimental results demonstrated that the magnetorheological (MR) effect of anisotropic MREs-based Silicone/SAIB was 126 % as compared to isotropic MREs-based Silicone/SAIB, 64%. The fabricated MREs samples were frequency and strain dependent. The relative MR effect for both samples showed decreasing trend with the increment of strain amplitude and excitation frequency.

Hybrid Magnetorheological Elastomer, the Future of Gait Detection

This article aims to present a brief review on sensors used for gait detection in Ankle Foot Orthosis (AFO) application. Both the advantages and disadvantages of sensors such as EMG sensor, rotary encoder, foot switches, and force plate are highlighted in this article. Authors also addressed the four characteristics of sensors for gait detection; uniformity, installation, flexibility, and multi-measurement. In addition, the sensors were then compared based on the characteristics. The foot switch was identified as the most compatible sensor for gait detection. However, the sensor was also discovered to contain problems in its durability and uneven grounding. Consequently, the authors propose an introduction to a new material, hybrid Magnetorheological Elastomer (MRE). Coincidentally, the mentioned material possesses attributes of thin dimensions with adjustable stiffness. The thin dimension allows the hybrid MRE to be placed under the AFO sole. Furthermore, with an accurate degree of stiffness, the hybrid MRE allows for adjustment leading to a higher level of durability of the sensors which remains fine even if stomped on the user. In conclusion, the authors propose a further study on hybrid MRE AFO for the next study.

Magnetorheological Elastomer Silicone-Based Containing Corroded Carbonyl Iron Particles

In this study, magnetorheological elastomers (MREs) were synthesized using silicone rubber (SR) as the matrix element interspersed with 70 weight percent of corroded carbonyl iron particles (CIPs). The CIPs were corroded in dilute hydrochloric acid (HCl) for 4 hours. The rheological properties related to MR effect were experimentally examined in the absence and presence of magnetic field at various current using a rheometer. The experimental results depicted the MR effect of the MRE with corroded CIPs decreased one-half, 27% as compared to the non-corroded samples, 58%. The correlation between the purity of CIPs and storage modulus of MR elastomer is examined in this study.

Rheological properties of a reclaimed waste tire rubber through high-pressure high-temperature sintering

High-Pressure High-Temperature (HPHT) sintering method has successfully revulcanized waste tire rubber (WTR) without any additional virgin rubber. The crumb rubber cleaned from its fabric and metals was reclaimed by applying high pressure (25 MPa) and high temperature (200 °C) for an hour along with common vulcanization agents such as sulfur, zinc oxide, and stearic acid. Dynamic properties of reclaimed WTR were assessed through shear rheology test on MCR302 Rheometer, Anton Paar, Austria. The results indicated that under steady test, the yield stress occurred at 31 kPa at 5% linear viscoelastic limit. The storage modulus ranged from 0.6 to 0.7 MPa under excitation frequency of 0.1 to 100 Hz and 1% strain amplitude. Under ramp strain amplitude, the storage modulus showed Payne Effect phenomenon at 0.8 to 1 % strain amplitude and 1 Hz excitation frequency. In general, the resulted dynamic properties was comparable with non-reclaimed rubber based on a literature survey. The results confirmed that HPHT sinte...