Influences of electric field strength on rheological properties of electrorheological fluid based on hollow poly (O-phenylenediamine co O-toluidine) dispersed on silicone oil

Highlights

• Hollow poly (O-toluidine-co-O-phenylenediamine) (POT-Co-OPD) was synthesized via oxidative polymerization reaction.

• Fabricated nanoparticles were applied as a new electrorheological (ER) material.

• Their ER characteristics under various external electric field strengths were examined using a rotational rheometer.

• Their yield stresses were well correlated with universal yield stress equation.

Abstract

In this study, hollow poly (O-phenylenediamine-co-O-toluidine) (POPD-co-OT) was synthesized via oxidative polymerization reaction. The POPD-co-OT was decorated into polystyrene surface core spherical particles before removing the core to obtain the hollow particles. The chemical structure and morphology of the conducting POPD-co-OT were studied with FTIR spectroscopy, proton NMR, scanning electron microscopy, and TEM. The hollow particles were applied in the dispersion phase for the preparation of electrorheological fluid (ERF). The rheological properties were investigated with a rotational rheometer, whereas the chain formation inside the ERF was observed using OM. The experimental results indicated that the shear stress of ERF increased with increasing strength of the electric field and quickly responded by impacting the external electric field strength. The ERF system is quite stable for a long time up to 200 h.

Introduction

ERF is a type of smart material that the conducting or polarizable particles are well blended in an insulating liquid [[1], [2], [3], [4]]. The rheological behaviors can be easily altered from liquid- to solid-like by adjusting the external field strength because of the formation of chains inside the rheological fluid [5]. This changing occurred in milliseconds [6] and is reversible by removing the external electric field strength. The distribution of conducting particles is random with no external field strength and the electrorheological fluids (ERFs) exhibit Newtonian fluid characteristics. By attaching the external field strength, the dispersed phases are polarized before forming chains or columns as a result of interactions between particles. The viscosity of the ERF varies instantaneously by changing the external electric field strength. Some rheological ERF characteristics including of shear stress, modulus and shear viscosity were improved by increasing the electric field strength [7]. This improvement helped expand ERF applications in industrial fields like hydraulics, electronics, and robotics [[8], [9], [10], [11]].

Many dispersed materials such as core-shell structured particles, polymers, and inorganic particles have been successfully applied for the fabrication of ERF systems [[12], [13], [14], [15], [16]]. Conductive polymer-based materials have been also widely applied in the dispersion phase because of their advantages such as low electrical conductivity and a π-conjugated structure [[17], [18], [19]]. Polyaniline (PANI) and its derivatives were considered promising conducting polymers for ERF applications because of their low cost, easy preparation, excellent environment stability, and electric conductivity control [[20], [21], [22], [23], [24]]. Many types of PANI and its derivatives based on composite materials have been applied in the dispersion phase for ERF. The core/shell particles based on PANI were prepared and examined in detail with excellent response [[25], [26], [27]]. The high density of these phases was considered the primary disadvantage which induced ERF dispersion stability. This problem has been resolved with the use of many hollow low-density particles to replace the high-density core-shell particles [[28], [29], [30]].

In the present work, hollow poly (p-toluidine-co-p-phenylenediamine) was synthesized via simple method before being used in the dispersion phase in the ERF system. The poly (p-toluidine-co-p-phenylenediamine) shell was decorated onto the surface of a polystyrene core, which was previously synthesized via surfactant free emulsion polymerization. The PS particles were modified with sulfonic acid to form sulfonated PS spherical particles prior to coating with a conducting polymer shell. The toluidinium and phenylenediaminium ions were formed in an acidic medium and easily interacted with the sulfonate ion because of the well-coated layer of poly (p-toluidine-co-p-phenylenediamine) on the core of the PS spherical particles. The PS core was removed by proper solvent before obtaining the hollow conductive poly (POPD-co-OT). The ERF was fabricated by dispersion of a hollow conductive poly (POPD-co-OT) in a silicone oil medium with a high speed mechanical stirrer and ultrasonication technique. Many characteristics of the ERF system were investigated.