Magnetorheology of dimorphic magnetorheological fluids based on iron nanorods

The aim of this paper is to document suitability of partial substitution of magnetic carbonyl iron (CI) microspheres with iron nanorods to obtain dimorphic magnetorheological (MR) suspensions with comparable MR performance to conventional MR suspensions exclusively based on (CI) microspheres while the sedimentation stability is considerably improved. The morphology of CI and iron nanorods was analyzed via scanning electron microscopy and transmission electron microscopy, respectively, and magnetic properties via vibrating sample magnetometry. The steady shear flow and small-amplitude dynamic oscillatory shear measurements were carried out to confirm effective MR performance. The sedimentation test showed positive role of dimorphic composition of dispersed phase on the sedimentation stability. © Published under licence by IOP Publishing Ltd.Grant Agency of the Czech Republic [14-32114P]; Ministry of Education, Youth and Sports of the Czech Republic - Program NPU I [LO1504

A rheological evaluation of steady shear magnetorheological flow behavior using three-parameter viscoplastic models

Knowledge of the complicated flow characteristics of magnetorheological (MR) suspensions is necessary for simulations, calculations in engineering processes, or designing new devices utilizing these systems. In this study, we employed three constitutive equations (three-parameter models) for an evaluation of steady shear behavior of MR suspensions. The predictive/fitting capabilities of the Robertson-Stiff (R-S) model were compared with the commonly used Herschel-Bulkley (as a reference) and the Mizrahi-Berk models. The appropriateness of the models was examined using rheological data for diluted as well as concentrated MR systems. The effect of magnetic field strength on model fitting capabilities was also investigated. The suitability of the individual models was evaluated by observing correlation coefficient, sum of square errors, and root mean square errors. A statistical analysis demonstrated that the best fitting capabilities were exhibited by the R-S model, while others provided less accurate fits with the experimental data. Therefore, shear stresses and the yield stress predicted according to the R-S equation can be considered as the most accurate under defined conditions in comparison with the Herschel-Bulkley and the Mizrahi-Berk model predictions. We also showed that the consistency index obtained from the R-S model increased with increasing magnetic field and particle concentration, which physically reflected more rigid internal structures generated in MR suspensions upon an external magnetic field. This behavior was indistinguishable when other models were applied. © 2016 Author(s).Ministry of Education, Youth and Sports of the Czech Republic-Program NPU I [LO1504

The impact of polymer grafting from a graphene oxide surface on its compatibility with a PDMS matrix and the light-induced actuation of the composites

Poly(dimethyl siloxane) (PDMS)-based materials with improved photoactuation properties were prepared by the incorporation of polymer-grafted graphene oxide particles. The modification of the graphene oxide (GO) surface was achieved via a surface initiated atom transfer radical polymerization (SI ATRP) of methyl methacrylate and butyl methacrylate. The modification was confirmed by thermogravimetric analysis, infrared spectroscopy and electron microscopy. The GO surface reduction during the SI ATRP was investigated using Raman spectroscopy and conductivity measurements. Contact angle measurements, dielectric spectroscopy and dynamic mechanical analyses were used to investigate the compatibility of the GO filler with the PDMS matrix and the influence of the GO surface modification on its physical properties and the interactions with the matrix. Finally, the thermal conductivity and photoactuation properties of the PDMS matrix and composites were compared. The incorporation of GO with grafted polymer chains, especially poly(n-butyl methacrylate), into the PDMS matrix improved the compatibility of the GO filler with the matrix, increased the energy dissipation due to the improved flexibility of the PDMS chains, enhanced the damping behavior and increased the thermal conductivity. All the changes in the properties positively affected the photoactuation behavior of the PDMS composites containing polymer-grafted GO. © 2017 by the authors.LO1504, MOE, Ministry of EducationGrant Agency of the Czech Republic [16-20361Y]; Ministry of Education, Youth and Sports of the Czech Republic-program NPU I [LO1504]; SRDA [APVV-15-0545]; VEGA [VEGA 2/0161/17]; Slovak Academy of Sciences [SAS-MOST JRP 2014-9

Magnetorheology of core-shell carbonyl iron/ZnO rod-like particle silicone oil suspensions under oscillatory shear

The aim of this study is a preparation and application of inorganic coating on the surface of carbonyl iron particles. The two step solvothermal synthesis provides core-shell CI/ZnO rod-like morphology. Compact coating of particles has a slightly negative impact on their magnetic properties (measured for magnetic field strength in the range from 0 to 213 mT); however, there is a suitable magnetorheological performance investigated under oscillatory shear, suitable to be applied in real applications. © Published under licence by IOP Publishing Ltd

Comparison of electrorheological characteristics obtained in two geometrical arrangements: Parallel plates and concentric cylinders

The electrorheological characteristics of suspensions of PANI powders suspended in silicone oil measured by a rotational rheometer Physica MCR 501 (Anton Paar Co.) are compared for two different geometrical arrangements - parallel plates and concentric cylinders. The individual differences in the results of the measured parameters are discussed

Controllable reduction of graphene oxide/poly(Butyl acrylate) hybrids under ATRP conditions

This study is aimed on the controllable reduction of the graphene oxide (GO) sheets during surface initiated atom transfer radical polymerization (SI-ATRP). GO sheets were successfully synthesized using Hummers method and properly characterized by Fourier transform infrared spectroscopy (FTIR). SI-ATRP approach was used to simultaneously modify the GO surface by poly(butyl acrylate) (PBA) brushes and its chemical reduction in the single-step synthesis. The presence of the polymer brushes on the GO sheets was investigated by gel permeation chromatography, nuclear magnetic resonance and FTIR. Simultaneous GO reduction during polymerization was confirmed using Raman spectroscopy and finally by conductivity measurement. Compatibility of the GO and GO-PBA sheets was investigated via contact angle measurements of sessile drop between GO substrates and poly(dimethyl siloxane). From the potential applicability point of view, the modification of graphene-based hybrids by polymers is highly important especially when the compatibility as well as conductivity of GO-PBA sheets with surroundings plays a crucial role i.e. the light-stimulated sensors based on silicon or other elastomers.Grant Agency of the Czech Republic [16-20361Y]; Ministry of Education, Youth and Sports of the Czech Republic -program NPU I [LO1504]; [APVV-14-0891

Graphene oxide reduction during surface-initiated atom transfer radical polymerization of glycidyl methacrylate: Controlling electro-responsive properties

Unique grafting of the poly(glycidyl methacrylate) from the surface of graphene oxide (GO) with the controllable reduction of GO particles was performed in a single-step reaction using atom transfer radical polymerization technique. The control of the GO surface reduction and modification can be achieved by appropriate selection of the ratio between tertiary amine and GO particle contents. Finely tuned electrical conductivity of the GO-PGMA particles enables simple tailoring of electro-responsive properties of their silicone oil suspensions. © 2015 Elsevier B.V.Operational Program Research and Development for Innovations; European Regional Development Fund (ERDF); National Budget of the Czech Republic, within the framework of the project Centre of Polymer Systems [CZ.1.05/2.1.00/03.0111

A facile controllable coating of carbonyl iron particles with poly(glycidyl methacrylate): A tool for adjusting MR response and stability properties

This study is focused on the controllable coating of the carbonyl iron (CI) particles widely applied in magnetorheology. These particles were grafted with poly(glycidyl methacrylate) (PGMA) with narrow polydispersity via surface-initiated atom transfer radical polymerization. Two types of core-shell particles differing in molecular weights of grafted polymer chains were synthesized. The effect of shell thickness on the thermo-oxidation stability of particles as well as the sedimentation stability of their silicone oil suspensions was evaluated. The successful coating process was confirmed by Fourier transform infrared spectroscopy and energy-dispersive spectrometry. The differences in the magnetic properties of bare and coated CI particles were clarified through vibrating sample magnetometry. Due to the controllable length of the PGMA grafts, the magnetic properties remain almost the same as those for bare CI. The magnetorheological (MR) behavior of silicone oil suspensions containing 60 wt% of bare CI particles as well as PGMA-coated analogues was investigated in the absence and in the presence of various magnetic field strengths, demonstrating the negligible impact of surface modification on final MR performance. Thus, the grafting of the particles with PGMA negligibly affected magnetic properties but considerably enhanced thermo-oxidation and sedimentation stabilities. Finally, a novel tensiometric method for sedimentation stability measurements of MR suspensions was successfully implemented. This journal is © The Royal Society of Chemistry.specific university research resources [IGA/FT/2014/017]; Grant Agency of the Czech Republic [14-32114P]; Operational Program Research and Development for Innovations; European Regional Development Fund (ERDF); National Budget of Czech Republic [CZ.1.05/2.1.00/03.0111]; Centre of Excellence FUN-MA