Electrorheological analysis of nano laden suspensions

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Abstract

The synthesis and characterization of Pb3O2Cl2 nanowires and the electrorheological (ER) properties of carbon nanofiber (CNF), carbon nanotube (CNT) and Pb3O2Cl2 nanowire (NW) laden suspensions is presented. The ER properties were investigated through oscillatory shear experiments. The viscoelastic response in the presence of dc electric fields was analyzed. Actuation behavior for the CNF and NW laden suspensions was observed at low voltages and low concentration of the reinforcements (0.05 wt%). In the case of the CNT laden suspensions, an effect was observed at a concentration of 0.0125 wt%. Positive and negative electrorheological behaviors were observed due to differences in electrical conductivity and polarization mechanisms.

Graphical abstract

(A) HRTEM image and (B) corresponding electron diffraction pattern of a NW oriented with respect to the [001] zone axis showing belt growth in the [010] direction.

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Introduction

Nanostructures and nanoreinforced systems have led the revolution in the development of structures, devices and systems through continuous breakthroughs that will benefit fields such as medicine, biotechnology, information technology, environment, space, military and other areas of national importance. Fascinating research is being conducted to build “intelligence” in materials to provide structures that could learn, diagnose and prevent failure. Researchers are especially keen on nanomaterials as sensors and actuators. Recent results have shown that carbon nanotubes possess significant potential as solid-state actuators with mechanical response to applied electric fields [1], [2], [3], [4]. The discovery of carbon nanotubes (CNT), carbon nanofibers (CNF) and most recently the development of a variety of nanowire materials (NW) [5], [6], [7], including Si, Ge, and GaAs, is playing a key role in the progress of exciting research in nanoreinforced systems given their remarkable electrical and mechanical properties. CNT, CNF and NW can be electrically polarized and have the ability to be charged. These properties make them excellent prospective materials to develop “nonconventional” electrorheological fluids that could operate at the considerably low voltages needed for microactuators and switches.

The electrorheological (ER) effect, first described by Winslow in 1949, describes the response of a colloidal suspension (consisting of small solid particles dispersed in an insulating liquid) to applied electric fields (several kV/mm) [8]. The rheological parameters (i.e., viscosity and modulus) of the suspension can increase (positive ER effect) or decrease (negative ER effect), with tunable properties that are reversible once the field is removed. ER fluids basically translate electric signals into mechanical signals. The adoption of ER fluids in practical applications has been slow relative to magneto-rheological (MR) fluids, which have found exciting applications as dampers, valves and locks in cars, bridges, building structures, digital cameras, artificial knees, and aeronautics, to mention some [9], [10]. However, MR fluids applications have also been hampered to some extent due to poor dispersion of the particles which results into settling and agglomeration. These problems are expected to be overcome with nanosize particle reinforcements. Recently, Poddar et al. published a study where iron particles of micrometer, nano, and hybrid (80% micrometer, 20% nano) size where dispersed in hydraulic oil and their MR response analyzed [11]. They observed that the hybrid system provided optimum response when considering aspects such as settling, yield stress and porosity [11]. MR fluids require much less energy to change their properties, though ER fluids have the advantage that they do not need magnets to be activated, a couple of electrodes are sufficient (though the need for such high voltages has created safety and reliability concerns).

In this study the synthesis and characterization of Pb3O2Cl2 nanowires and the electrorheological properties of carbon nanofiber, carbon nanotube, and nanowire laden suspensions is presented.

Section snippets

Materials

CNFs were kindly supplied by Applied Sciences, Inc. and were produced by the so-called vapor grown carbon fiber method and purified following procedures developed by Lozano et al. [12]. Single wall carbon nanotubes (CNTs) were obtained from Carbon Nanotechnologies, Inc. (CNI) with a metal content of 15 wt% (residuals). Silicone oil was used as the host insulating medium. The oil was obtained from Fisher Scientific with a density of 0.9630 g/cm3, a viscosity of 50 centistokes and a relative

Analysis of the Pb3O2Cl2 nanowires

The SEM image presented in Fig. 1A shows the Pb3O2Cl2 nanowires produced. It is observed that individual nanowires range in length from 4 up to 20 μm with diameters ranging from 14 to 170 nm. High-resolution SEM images (Fig. 1B) show that the wires have a belt-like morphology and tend to bundle together into groups when drop cast onto a glassy carbon substrate as also observed by LRTEM (Fig. 1C). Fig. 2 shows the XRD pattern obtained from a thin film of the nanowires deposited onto a quartz

Acknowledgements

Financial support to K. Lozano from National Science Foundation (NSF) under CAREER Grant CMS-0092621 is gratefully acknowledged. B. Korgel acknowledges financial support from Robert A. Welch Foundation and the Advanced Materials Research Center in collaboration with International SEMATECH.

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