Displaying publications 1 - 20 of 28 in total

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  1. Fulltext Ertapenem-induced neurotoxicity in an end-stage renal disease patient on intermittent haemodialysis: a case report
    Shahar S, Arimuthu DA, Mazlan SA
    BMC Nephrol, 2022 Nov 08;23(1):360.
    PMID: 36348388 DOI: 10.1186/s12882-022-02980-8
    BACKGROUND: Carbapenem-induced neurotoxicity is an unusual side effect, with seizure being the most commonly reported symptom. Among the carbapenems, imipenem-cilastin is classically associated with the most severe neurotoxicity side effects. Carbapenem is mainly excreted by the kidney and its half-life is significantly increased in patients with chronic kidney disease (CKD). Therefore, dose adjustment is necessary in such patients. Ertapenem-associated neurotoxicity is increasingly being reported in CKD patients, but rarely seen in patients with recommended dose adjustment.

    CASE PRESENTATION: We report a case of a 56-year-old male patient with chronic kidney disease 5 on dialysis(CKD 5D). The patient presented with a history of fever, chills and rigours during a session of haemodialysis (HD). He was diagnosed with Enterobacter cloacae catheter-related blood stream infection and was started on ertapenem. After 13 days of ertapenem, he experienced an acute confusional state and progressed to having auditory and visual hallucinations. His blood investigations and imaging results revealed no other alternative diagnosis. Hence a diagnosis of ertapenem-induced neurotoxicity was made. He had complete resolution of symptoms after 10 days' discontinuation of ertapenem.

    CONCLUSION: Our case draws attention to the risk of potentially serious toxicity of the central nervous system in HD patients who receive the current recommended dose of ertapenem. It also highlights that renal dosing in CKD 5D patients' needs to be clinically studied to ensure antibiotic safety.

  2. Fulltext A comparative work on the magnetic field-dependent properties of plate-like and spherical iron particle-based magnetorheological grease
    Mohamad N, Ubaidillah, Mazlan SA, Imaduddin F, Choi SB, Yazid IIM
    PLoS One, 2018;13(4):e0191795.
    PMID: 29630595 DOI: 10.1371/journal.pone.0191795
    In this study, a new magnetorheological (MR) grease was made featuring plate-like carbonyl iron (CI) particles, and its magnetic field-dependent rheological properties were experimentally characterized. The plate-like CI particles were prepared through high-energy ball milling of spherical CI particles. Then, three different ratios of the CI particles in the MR grease, varying from 30 to 70 wt% were mixed by dispersing the plate-like CI particles into the grease medium with a mechanical stirrer. The magnetic field-dependent rheological properties of the plate-like CI particle-based MR grease were then investigated using a rheometer by changing the magnetic field intensity from 0 to 0.7 T at room temperature. The measurement was undertaken at two different modes, namely, a continuous shear mode and oscillation mode. It was shown that both the apparent viscosity and storage modulus of the MR grease were heavily dependent on the magnetic field intensity as well as the CI particle fraction. In addition, the differences in the yield stress and the MR effect between the proposed MR grease featuring the plate-like CI particles and the existing MR grease with the spherical CI particles were investigated and discussed in detail.
  3. A study of intima media thickness and their cardiovascular risk factors in patients with psoriatic arthritis
    Mazlan SA, bin Mohamed Said MS, Hussein H, binti Shamsuddin K, Shah SA, Basri H
    Acta Medica (Hradec Kralove), 2009;52(3):107-16.
    PMID: 20073422 DOI: 10.14712/18059694.2016.114
    INTRODUCTION: Psoriatic Arthritis (PsA) is an inflammatory arthritis associated with Psoriasis. Its recognition as an inflammatory disease distinct from Rheumatoid Arthritis has put forward for consideration several questions regarding its specific CVS mortality and morbidity (9, 11, 16, 26). Carotid intima media thickness is a useful surrogate and sensitive marker to determine atherosclerosis even in its subclinical stages (6, 14, 22, 27, 32).

    OBJECTIVE: Prevalence of carotid intima media thickness in patients with Psoriatic arthritis is unknown in Asian population. We aim to identify the presence of subclinical atherosclerosis in patients with psoriatic arthritis and disease activity association and its predictors in a series of patients with PsA attended to the rheumatology clinic, tertiary hospitals.

    METHODS: A total of 63 patients with PsA who fulfilled the CASPAR criteria were recruited from UKM Medical Centre and Hospital Putrajaya. Common carotid intima media thickness (IMT) was measured in both right and left carotid artery by using high resolution B-mode ultrasound. This was a cross sectional study first done in Malaysia for PsA patients.

    RESULTS: The positive IMT (IMT > 1.00 mm) among PsA was observed in 10 out of 63 patients (15.9 %) regardless of background cardiovascular risk. The mean +/- SD of IMT was 0.725 +/-0.260 mm for this study. Variables significantly associated with positive IMT (p < 0.05) included age at the time of study (p = 0.005), waist circumference (p = 0.001), Hypertension (p = 0.007), Diabetes (p = 0.002) and Metabolic syndrome (p = 0.001) and not associated with gender, ethnicity, duration of PsA disease, pattern of PsA, disease activity and severity. Above all, only age had positive IMT independent predictor (p = 0.032), with OR 1.116; 95 % CI (1.010-1.234).

    CONCLUSIONS: There was a significant association between CVS risk and positive Intima Media Thickness in Psoriatic Arthritis patients. Otherwise, there was no association in disease activity, disease severity and DMARDS therapy with positive Intima Media Thickness in Psoriatic Arthritis patients. The study was approved by Research and Ethics Committee of the faculty of medicine, Universiti Kebangsaan Malaysia with project code FF-114-2008 and by Community Research Center (CRC) of National Institutes of Health (NIH) for the case study in Hospital Putrajaya with the project code NMRR-08-970-2125.
  4. Fulltext Sensitivities of Rheological Properties of Magnetoactive Foam for Soft Sensor Technology
    Norhaniza R, Mazlan SA, Ubaidillah U, Sedlacik M, Aziz SAA, Nazmi N, et al.
    Sensors (Basel), 2021 Feb 28;21(5).
    PMID: 33670872 DOI: 10.3390/s21051660
    Magnetoactive (MA) foam, with its tunable mechanical properties and magnetostriction, has the potential to be used for the development of soft sensor technology. However, researchers have found that its mechanical properties and magnetostriction are morphologically dependent, thereby limiting its capabilities for dexterous manipulation. Thus, in this work, MA foam was developed with additional capabilities for controlling its magnetostriction, normal force, storage modulus, shear stress and torque by manipulating the concentration of carbonyl iron particles (CIPs) and the magnetic field with regard to morphological changes. MA foams were prepared with three weight percentages of CIPs, namely, 35 wt.%, 55 wt.% and 75 wt.%, and three different modes, namely, zero shear, constant shear and various shears. The results showed that the MA foam with 75 wt.% of CIPs enhanced the normal force sensitivity and positive magnetostriction sensitivity by up to 97% and 85%, respectively. Moreover, the sensitivities of the storage modulus, torque and shear stress were 8.97 Pa/mT, 0.021 µN/mT, and 0.0096 Pa/mT, respectively. Meanwhile, the magnetic dipolar interaction between the CIPs was capable of changing the property of MA foam from a positive to a negative magnetostriction under various shear strains with a low loss of energy. Therefore, it is believed that this kind of highly sensitive MA foam can potentially be implemented in future soft sensor systems.
  5. Fulltext Physicochemical characterization and rheological properties of magnetic elastomers containing different shapes of corroded carbonyl iron particles
    Burhannuddin NL, Nordin NA, Mazlan SA, Aziz SAA, Kuwano N, Jamari SKM, et al.
    Sci Rep, 2021 Jan 13;11(1):868.
    PMID: 33441824 DOI: 10.1038/s41598-020-80539-z
    Carbonyl iron particles (CIPs) is one of the key components in magnetic rubber, known as magnetorheological elastomer (MRE). Apart from the influence of their sizes and concentrations, the role of the particle' shape is pronounced worthy of the attention for the MRE performance. However, the usage of CIPs in MRE during long-term applications may lead to corrosion effects on the embedded CIPs, which significantly affects the performance of devices or systems utilizing MRE. Hence, the distinctions between the two types of MRE embedded in different shapes of spherical and plate-like CIPs, at both conditions of non-corroded and corroded CIPs were investigated in terms of the field-dependent rheological properties of MRE. The plate-like shape was produced from spherical CIPs through a milling process using a rotary ball mill. Then, both shapes of CIPs individually subjected to an accelerated corrosion test in diluted hydrochloric (HCl) at different concentrations, particularly at 0.5, 1.0, and 1.5 vol.% for 30 min of immersion time. Eight samples of CIPs, including non-corroded for both CIPs shapes, were characterized in terms of a morphological study by field emission scanning electron microscope (FESEM) and magnetic properties via vibrating sample magnetometer (VSM). The field-dependent rheological properties of MREs were analyzed the change in the dynamic modulus behavior of MREs via rheometer. From the application perspective, this finding may be useful for the system to be considered that provide an idea to prolong the performance MRE by utilizing the different shapes of CIPs even when the material is fading.
  6. Fulltext The Effect of Sr-CoFe2O4 Nanoparticles with Different Particles Sized as Additives in CIP-Based Magnetorheological Fluid
    Nugroho KC, Ubaidillah U, Arilasita R, Margono M, Priyambodo BH, Purnama B, et al.
    Materials (Basel), 2021 Jul 01;14(13).
    PMID: 34279258 DOI: 10.3390/ma14133684
    This study investigated the effect of adding strontium (Sr)-doped cobalt ferrite (CoFe2O4) nanoparticles in carbonyl iron particle (CIP)-based magnetorheological fluids (MRFs). Sr-CoFe2O4 nanoparticles were fabricated at different particle sizes using co-precipitation at calcination temperatures of 300 and 400 °C. Field emission scanning electron microscopy (FESEM) was used to evaluate the morphology of the Sr-CoFe2O4 nanoparticles, which were found to be spherical. The average grain sizes were 71-91 nm and 118-157 nm for nanoparticles that had been calcinated at 300 and 400 °C, respectively. As such, higher calcination temperatures were found to produce larger-sized Sr-CoFe2O4 nanoparticles. To investigate the rheological effects that Sr-CoFe2O4 nanoparticles have on CIP-based MRF, three MRF samples were prepared: (1) CIP-based MRF without nanoparticle additives (CIP-based MRF), (2) CIP-based MRF with Sr-CoFe2O4 nanoparticles calcinated at 300 °C (MRF CIP+Sr-CoFe2O4-T300), and (3) CIP-based MRF with Sr-CoFe2O4 nanoparticles calcinated at 400 °C (MRF CIP+Sr-CoFe2O4-T400). The rheological properties of these MRF samples were then observed at room temperature using a rheometer with a parallel plate at a gap of 1 mm. Dispersion stability tests were also performed to determine the sedimentation ratio of the three CIP-based MRF samples.
  7. Fulltext The Effect of Particle Shapes on the Field-Dependent Rheological Properties of Magnetorheological Greases
    Mohamad N, Ubaidillah, Mazlan SA, Choi SB, Abdul Aziz SA, Sugimoto M
    Int J Mol Sci, 2019 Mar 27;20(7).
    PMID: 30934679 DOI: 10.3390/ijms20071525
    The transient response of magnetorheological (MR) materials, in general, is very important for design consideration in MR-based devices. Better response to magnetic fields is beneficial for a better response rate to the electrical current applied in the electromagnetic coil. As a result, MR-based devices would have a high response to external stimuli. In this work, the principal characteristics of magnetorheological greases (MRGs) which have two different particle shapes are experimentally investigated. One type of particle distributed in the grease medium is conventional spherical-shaped carbonyl iron (CI) particles, while the other is plate-like CI particles made using a high-energy rotary ball mill from spherical CI particles. A set of bidisperse MRG samples are firstly prepared by adjusting the weight percentage of the plate-like CI particles and mixing with the spherical CI particles. Subsequently, three important properties of MRGs in terms of their practical application are measured and compared between the two different particle shapes. The field-dependent apparent viscoelastic properties of the prepared MRG samples are measured, followed by the field-dependent storage and loss moduli using an oscillatory shear rheometer. In addition, the transient response time, which indicates the speed in the actuating period of MRGs, is measured by changing the strain amplitude. Then, a comparative assessment on the three properties are undertaken between two different particle shapes by presenting the corresponding results in the same plot. It is shown that the bidisperse MRG with plate-like CI particles exhibits an increase in the initial apparent viscosity as well as stiffness property compared to the MRG with spherical particles only.
  8. Fulltext Thermal Stability and Rheological Properties of Epoxidized Natural Rubber-Based Magnetorheological Elastomer
    Yunus NA, Mazlan SA, Ubaidillah, Abdul Aziz SA, Tan Shilan S, Abdul Wahab NA
    Int J Mol Sci, 2019 Feb 10;20(3).
    PMID: 30744210 DOI: 10.3390/ijms20030746
    Determination of the thermal characteristics and temperature-dependent rheological properties of the magnetorheological elastomers (MREs) is of paramount importance particularly with regards to MRE applications. Hitherto, a paucity of temperature dependent analysis has been conducted by MRE researchers. In this study, an investigation on the thermal and rheological properties of epoxidized natural rubber (ENR)-based MREs was performed. Various percentages of carbonyl iron particles (CIPs) were blended with the ENR compound using a two roll-mill for the preparation of the ENR-based MRE samples. The morphological, elemental, and thermal analyses were performed before the rheological test. Several characterizations, as well as the effects of the strain amplitude, temperature, and magnetic field on the rheological properties of ENR-based MRE samples, were evaluated. The micrographs and elemental results were well-correlated regarding the CIP and Fe contents, and a uniform distribution of CIPs was achieved. The results of the thermal test indicated that the incorporation of CIPs enhanced the thermal stability of the ENR-based MREs. Based on the rheological analysis, the storage modulus and loss factor were dependent on the CIP content and strain amplitude. The effect of temperature on the rheological properties revealed that the stiffness of the ENR-based MREs was considered stable, and they were appropriate to be employed in the MRE devices exposed to high temperatures above 45 °C.
  9. Fulltext Effects of Petroleum-Based Oils as Dispersing Aids on Physicochemical Characteristics of Magnetorheological Elastomers
    Muhammad Zaki N, Yunus NA, Yusoff MS, Mazlan SA, Abdul Aziz SA, Izni NA, et al.
    Materials (Basel), 2021 Nov 19;14(22).
    PMID: 34832425 DOI: 10.3390/ma14227026
    This paper investigated the effects of petroleum-based oils (PBOs) as a dispersing aid on the physicochemical characteristics of natural rubber (NR)-based magnetorheological elastomers (MREs). The addition of PBOs was expected to overcome the low performance of magnetorheological (MR) elastomers due to their inhomogeneous dispersion and the mobility of magnetic particles within the elastomer matrix. The NR-based MREs were firstly fabricated by mixing the NR compounds homogeneously with different ratios of naphthenic oil (NO), light mineral oil (LMO), and paraffin oil (PO) to aromatic oil (AO), with weight percentage ratios of 100:0, 70:30, 50:50, and 30:70, respectively. From the obtained results, the ratios of NO mixed with low amounts of AO improved the material physicochemical characteristics, such as thermal properties. Meanwhile, LMO mixed the AO led to the best results for curing characteristics, microstructure observation, and magnetic properties of the MREs. We found that the LMO mixed with a high content of AO could provide good compatibility between the rubber molecular and magnetic particles due to similar chemical structures, which apparently enhance the physicochemical characteristics of MREs. In conclusion, the 30:70 ratio of LMO:AO is considered the preferable dispersing aid for MREs due to structural compounds present in the oil that enhance the physicochemical characteristics of the NR-based MREs.
  10. Fulltext Declining Performance of Silicone-Based Magnetorheological Elastomers after Accelerated Weathering
    Wibowo W, Lenggana BW, Ubaidillah U, Ariawan D, Imaduddin F, Mazlan SA, et al.
    Materials (Basel), 2021 Oct 25;14(21).
    PMID: 34771915 DOI: 10.3390/ma14216389
    Magnetorheological elastomers (MRE)-based products are usually located in an area directly exposed to sunlight and rain. However, there is no specific research on the behavior of MRE after accelerated weathering. Therefore, in this study, the changes to the chemical and rheological properties of both isotropic and anisotropic MRE after accelerated weathering were examined. Treated and untreated specimens were compared. MRE specimens with 40% by weight CIP were prepared with no current excitation and another sample was prepared with 1.5 T of magnetic flux density. Each specimen was treated in an accelerated weathering machine, Q-Sun Xe-1 Xenon Test Chamber, under a UV light exposure cycle and water spray. A material characterization was carried out using FTIR and a rheometer to determine the changes to the chemical and rheological properties. The morphological analysis results showed that after the weather treatment, the surface was rough and more cavities occurred. The rheometer test results showed a significant decrease in the storage modulus of each treated MRE specimen, unlike the untreated MRE specimens. The decrease in the storage modulus value with currents of 0, 1, 2, and 3 Amperes was 66.67%, 78.9%, 85.2%, and 80.5%, respectively. Meanwhile, FTIR testing showed a change in the wave peak between the untreated and treated MRE specimens. Thermogravimetric analysis (TGA) also showed a decrease in MRE weight for each specimen. However, for both treated and untreated MRE specimens, the decrease in TGA was not significantly different. In all the tests carried out on the MRE samples, weather acceleration treatment caused significant changes. This is an important consideration for developers who choose silicone as the MRE matrix.
  11. Fulltext Morphological Effects of Strain Localization in the Elastic Region of Magnetorheological Elastomers
    Johari MAF, Mazlan SA, Nordin NA, Choi SB, Aziz SAA, Daud S, et al.
    Materials (Basel), 2022 Dec 01;15(23).
    PMID: 36500061 DOI: 10.3390/ma15238565
    Strain localization is a significant issue that poses interesting research challenges in viscoelastic materials because it is difficult to accurately predict the damage evolution behavior. Over time, the damage mechanism in the amorphous structure of viscoelastic materials leads to subsequent localization into a shear band, gradually jeopardizing the materials' elastic sustainability. The primary goal of this study is to further understand the morphological effects and the role of shear bands in viscoelastic materials precipitated by strain localization. The current study aims to consolidate the various failure mechanisms of a sample and its geometry (surface-to-volume ratio) used in torsional testing, as well as to understand their effects on stress relaxation durability performance. A torsional shear load stress relaxation durability test was performed within the elastic region on an isotropic viscoelastic sample made of silicon rubber and a 70% weight fraction of micron-sized carbonyl iron particles. Degradation was caused by a shear band of localized plasticity that developed microscopically due to stress relaxation durability. The failure pattern deteriorated as the surface-to-volume ratio decreased. A field-emission scanning electron microscope (FESEM) and a tapping-mode atomic force microscope (AFM) were used for further observation and investigation of the sample. After at least 7500 cycles of continuous shearing, the elastic sustainability of the viscoelastic materials microstructurally degraded, as indicated by a decline in stress performance over time. Factors influencing the formation of shear bands were observed in postmortem, which was affected by simple micromanipulation of the sample geometry, making it applicable for practical implementation to accommodate any desired performance and micromechanical design applications.
  12. Fulltext A Review of Classification Techniques of EMG Signals during Isotonic and Isometric Contractions
    Nazmi N, Abdul Rahman MA, Yamamoto S, Ahmad SA, Zamzuri H, Mazlan SA
    Sensors (Basel), 2016 Aug 17;16(8).
    PMID: 27548165 DOI: 10.3390/s16081304
    In recent years, there has been major interest in the exposure to physical therapy during rehabilitation. Several publications have demonstrated its usefulness in clinical/medical and human machine interface (HMI) applications. An automated system will guide the user to perform the training during rehabilitation independently. Advances in engineering have extended electromyography (EMG) beyond the traditional diagnostic applications to also include applications in diverse areas such as movement analysis. This paper gives an overview of the numerous methods available to recognize motion patterns of EMG signals for both isotonic and isometric contractions. Various signal analysis methods are compared by illustrating their applicability in real-time settings. This paper will be of interest to researchers who would like to select the most appropriate methodology in classifying motion patterns, especially during different types of contractions. For feature extraction, the probability density function (PDF) of EMG signals will be the main interest of this study. Following that, a brief explanation of the different methods for pre-processing, feature extraction and classifying EMG signals will be compared in terms of their performance. The crux of this paper is to review the most recent developments and research studies related to the issues mentioned above.
  13. Fulltext Solvent Dependence of the Rheological Properties in Hydrogel Magnetorheological Plastomer
    Hapipi NM, Mazlan SA, Ubaidillah U, Abdul Aziz SA, Ahmad Khairi MH, Nordin NA, et al.
    Int J Mol Sci, 2020 Mar 05;21(5).
    PMID: 32151055 DOI: 10.3390/ijms21051793
    Chemically crosslinked hydrogel magnetorheological (MR) plastomer (MRP) embedded with carbonyl iron particles (CIPs) exhibits excellent magnetic performance (MR effect) in the presence of external stimuli especially magnetic field. However, oxidation and desiccation in hydrogel MRP due to a large amount of water content as a dispersing phase would limit its usage for long-term applications, especially in industrial engineering. In this study, different solvents such as dimethyl sulfoxide (DMSO) are also used to prepare polyvinyl alcohol (PVA) hydrogel MRP. Thus, to understand the dynamic viscoelastic properties of hydrogel MRP, three different samples with different solvents: water, DMSO, and their binary mixtures (DMSO/water) were prepared and systematically carried out using the oscillatory shear. The outcomes demonstrate that the PVA hydrogel MRP prepared from precursor gel with water shows the highest MR effect of 15,544% among the PVA hydrogel MRPs. However, the samples exhibit less stability and tend to oxidise after a month. Meanwhile, the samples with binary mixtures (DMSO/water) show an acceptable MR effect of 11,024% with good stability and no CIPs oxidation. Otherwise, the sample with DMSO has the lowest MR effect of 7049% and less stable compared to the binary solvent samples. This confirms that the utilisation of DMSO as a new solvent affects the rheological properties and stability of the samples.
  14. Fulltext Systematic Review on the Effects, Roles and Methods of Magnetic Particle Coatings in Magnetorheological Materials
    Jamari SKM, Nordin NA, Ubaidillah, Aziz SAA, Nazmi N, Mazlan SA
    Materials (Basel), 2020 Nov 24;13(23).
    PMID: 33255343 DOI: 10.3390/ma13235317
    Magnetorheological (MR) material is a type of magneto-sensitive smart materials which consists of magnetizable particles dispersed in a carrier medium. Throughout the years, coating on the surface of the magnetic particles has been developed by researchers to enhance the performance of MR materials, which include the improvement of sedimentation stability, enhancement of the interaction between the particles and matrix mediums, and improving rheological properties as well as providing extra protection against oxidative environments. There are a few coating methods that have been employed to graft the coating layer on the surface of the magnetic particles, such as atomic transfer radical polymerization (ATRP), chemical oxidative polymerization, and dispersion polymerization. This paper investigates the role of particle coating in MR materials with the effects gained from grafting the magnetic particles. This paper also discusses the coating methods employed in some of the works that have been established by researchers in the particle coating of MR materials.
  15. Fulltext Enhancement of Particle Alignment Using Silicone Oil Plasticizer and Its Effects on the Field-Dependent Properties of Magnetorheological Elastomers
    Khairi MHA, Fatah AYA, Mazlan SA, Ubaidillah U, Nordin NA, Ismail NIN, et al.
    Int J Mol Sci, 2019 Aug 21;20(17).
    PMID: 31438576 DOI: 10.3390/ijms20174085
    The existing mold concept of fabricating magnetorheological elastomer (MRE) tends to encounter several flux issues due to magnetic flux losses inside the chamber. Therefore, this paper presents a new approach for enhancing particle alignment through MRE fabrication as a means to provide better rheological properties. A closed-loop mold, which is essentially a fully guided magnetic field inside the chamber, was designed in order to strengthen the magnetic flux during the curing process with the help of silicone oil (SO) plasticizers. The oil serves the purpose of softening the matrix. Scanning electron microscopy (SEM) was used to observe the surface morphology of the fabricated MRE samples. The field-dependent dynamic properties of the MREs were measured several ways using a rheometer, namely, strain sweep, frequency sweep, and magnetic field sweep. The analysis implied that the effectiveness of the MRE was associated with the use of the SO, and the closed-loop mold helped enhance the absolute modulus up to 0.8 MPa. The relative magnetorheological (MR) effects exhibited high values up to 646%. The high modulus properties offered by the MRE with SO are believed to be potentially useful in industry applications, particularly as vibration absorbers, which require a high range of stiffness.
  16. Fulltext Microstructural behavior of magnetorheological elastomer undergoing durability evaluation by stress relaxation
    Johari MAF, Mazlan SA, Nasef MM, Ubaidillah U, Nordin NA, Aziz SAA, et al.
    Sci Rep, 2021 May 25;11(1):10936.
    PMID: 34035434 DOI: 10.1038/s41598-021-90484-0
    The widespread use of magnetorheological elastomer (MRE) materials in various applications has yet to be limited due to the fact that there are substantial deficiencies in current experimental and theoretical research on its microstructural durability behavior. In this study, MRE composed of silicon rubber (SR) and 70 wt% of micron-sized carbonyl iron particles (CIP) was prepared and subjected to stress relaxation evaluation by torsional shear load. The microstructure and particle distribution of the obtained MRE was evaluated by a field emission scanning electron microscopy (FESEM). The influence of constant low strain at 0.01% is the continuing concern within the linear viscoelastic (LVE) region of MRE. Stress relaxation plays a significant role in the life cycle of MRE and revealed that storage modulus was reduced by 8.7%, normal force has weakened by 27%, and stress performance was reduced by 6.88% along approximately 84,000 s test duration time. This time scale was the longest ever reported being undertaken in the MRE stress relaxation study. Novel micro-mechanisms that responsible for the depleted performance of MRE was obtained by microstructurally observation using FESEM and in-phase mode of atomic force microscope (AFM). Attempts have been made to correlate strain localization produced by stress relaxation, with molecular deformation in MRE amorphous matrix. Exceptional attention was focused on the development of molecular slippage, disentanglement, microplasticity, microphase separation, and shear bands. The relation between these microstructural phenomena and the viscoelastic properties of MRE was diffusely defined and discussed. The presented MRE is homogeneous with uniform distribution of CIP. The most significant recent developments of systematic correlation between the effects of microstructural deformation and durability performance of MRE under stress relaxation has been observed and evaluated.
  17. Fulltext Rheological Performance of Magnetorheological Grease with Embedded Graphite Additives
    Mohd Nasir NA, Nazmi N, Mohamad N, Ubaidillah U, Nordin NA, Mazlan SA, et al.
    Materials (Basel), 2021 Sep 06;14(17).
    PMID: 34501180 DOI: 10.3390/ma14175091
    The use of highly viscous grease as a medium in magnetorheological grease (MRG) provides the benefit of avoiding sedimentation from occurring. However, it limits the expansion of yield stress in the on-state condition, thus reducing the application performance during operation. Therefore, in this study, the improvement in the rheological properties of MRG was investigated through the introduction of graphite as an additive. MRG with 10 wt % graphite (GMRG) was fabricated, and its properties were compared to a reference MRG sample. The microstructure of GMRG was characterized using an environmental scanning electron microscope (ESEM). The rheological properties of both samples, including apparent viscosity, yield stress, and viscoelasticity, were examined using a shear rheometer in rotational and oscillatory modes. The results demonstrated a slight increase in the apparent viscosity in GMRG and a significant improvement in yield stress by 38.8% at 3 A with growth about 32.7% higher compared to MRG from 0 to 3 A. An expansion of the linear viscoelastic region (LVE) from 0.01% to 0.1% was observed for the GMRG, credited to the domination of the elastic properties on the sample. These obtained results were confirmed based on ESEM, which described the contribution of graphite to constructing a more stable chain structure in the GMRG. In conclusion, the findings highlight the influence of the addition of graphite on improving the rheological properties of MRG. Hence, the addition of graphite in MRG shows the potential to be applied in many applications in the near future.
  18. Fulltext An Insight into Amorphous Shear Band in Magnetorheological Solid by Atomic Force Microscope
    Johari MAF, Sarman AM, Mazlan SA, U U, Nordin NA, Abdul Aziz SA, et al.
    Materials (Basel), 2021 Aug 05;14(16).
    PMID: 34442907 DOI: 10.3390/ma14164384
    Micro mechanism consideration is critical for gaining a thorough understanding of amorphous shear band behavior in magnetorheological (MR) solids, particularly those with viscoelastic matrices. Heretofore, the characteristics of shear bands in terms of formation, physical evolution, and response to stress distribution at the localized region have gone largely unnoticed and unexplored. Notwithstanding these limitations, atomic force microscopy (AFM) has been used to explore the nature of shear band deformation in MR materials during stress relaxation. Stress relaxation at a constant low strain of 0.01% and an oscillatory shear of defined test duration played a major role in the creation of the shear band. In this analysis, the localized area of the study defined shear bands as varying in size and dominantly deformed in the matrix with no evidence of inhibition by embedded carbonyl iron particles (CIPs). The association between the shear band and the adjacent zone was further studied using in-phase imaging of AFM tapping mode and demonstrated the presence of localized affected zone around the shear band. Taken together, the results provide important insights into the proposed shear band deformation zone (SBDZ). This study sheds a contemporary light on the contentious issue of amorphous shear band deformation behavior and makes several contributions to the current literature.
  19. Fulltext Material Characterization of a Magnetorheological Fluid Subjected to Long-Term Operation in Damper
    Utami D, Ubaidillah, Mazlan SA, Imaduddin F, Nordin NA, Bahiuddin I, et al.
    Materials (Basel), 2018 Nov 06;11(11).
    PMID: 30404193 DOI: 10.3390/ma11112195
    This paper investigates the field-dependent rheological properties of magnetorheological (MR) fluid used to fill in MR dampers after long-term cyclic operation. For testing purposes, a meandering MR valve was customized to create a double-ended MR damper in which MR fluid flowed inside the valve due to the magnetic flux density. The test was conducted for 170,000 cycles using a fatigue dynamic testing machine which has 20 mm of stroke length and 0.4 Hz of frequency. Firstly, the damping force was investigated as the number of operating cycles increased. Secondly, the change in viscosity of the MR fluid was identified as in-use thickening (IUT). Finally, the morphological observation of MR particles was undertaken before and after the long-term operation. From these tests, it was demonstrated that the damping force increased as the number of operating cycles increases, both when the damper is turn on (on-state) and off (off-state). It is also observed that the particle size and shape changed due to the long operation, showing irregular particles.
  20. Fulltext Enhancement of Viscoelastic and Electrical Properties of Magnetorheological Elastomers with Nanosized Ni-Mg Cobalt-Ferrites as Fillers
    Abdul Aziz SA, Mazlan SA, Ubaidillah U, Shabdin MK, Yunus NA, Nordin NA, et al.
    Materials (Basel), 2019 Oct 28;12(21).
    PMID: 31661837 DOI: 10.3390/ma12213531
    Carbon-based particles, such as graphite and graphene, have been widely used as a filler in magnetorheological elastomer (MRE) fabrication in order to obtain electrical properties of the material. However, these kinds of fillers normally require a very high concentration of particles to enhance the conductivity property. Therefore, in this study, the nanosized Ni-Mg cobalt ferrite is introduced as a filler to soften MRE and, at the same time, improve magnetic, rheological, and conductivity properties. Three types of MRE samples without and with different compositions of Mg, namely Co0.5Ni0.2Mg0.3Fe2O4 (A1) and Co0.5Ni0.1Mg0.4Fe2O4 (A2), are fabricated. The characterization related to the micrograph, magnetic, and rheological properties of the MRE samples are analyzed using scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), and the rheometer. Meanwhile, the effect of the nanosized Ni-Mg cobalt ferrites on the electrical resistance property is investigated and compared with the different Mg compositions. It is shown that the storage modulus of the MRE sample with the nanosized Ni-Mg cobalt ferrites is 43% higher than that of the MRE sample without the nanomaterials. In addition, it is demonstrated that MREs with the nanosized Ni-Mg cobalt ferrites exhibit relatively low electrical resistance at the on-state as compared to the off-state condition, because MRE with a higher Mg composition shows lower electrical resistance when higher current flow occurs through the materials. This salient property of the proposed MRE can be effectively and potentially used as an actuator to control the viscoelastic property of the magnetic field or sensors to measure the strain of the flexible structures by the electrical resistance signal.
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