Strain-hardening in the oscillatory shear deformation of a dedoped polyaniline electrorheological fluid
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An electrorheological (ER) fluid, consisting of polydisperse dedoped polyaniline (PANI) particles, having irregular shapes, dispersed in silicone oil, was subjected to cyclic strain annealing treatments using oscillatory shear, under an external electric field. After each annealing period, the sample was subjected to a controlled-strain sweep, to determine the yield stress, and to erase the ER structure. During each annealing cycle, the storage modulus and the yield stress were observed to increase, and the loss modulus to decrease, each eventually approaching an asymptotic constant value. These observations in oscillatory shear complement our previous observations of a strain-hardening effect in a PANI/silicone oil ER fluid subjected to unidirectional creep tests.
KeywordsPANI Oscillatory Shear Yield Strain Primary Chain Nonlinear Viscoelasticity
The authors (PH and AS) would like to acknowledge the financial support provided by the Thailand Research Fund (TRF, RGJ Grant No. PHD/0234/2544 and BRG grant), Conductive & Electroactive Polymers Research Unit and KFAS of Chulalongkorn University, the Royal Thai Government (Budget of Fiscal Year 2550), and the Petroleum Petrochemical and Advanced Materials Consortium. AMJ also wishes to acknowledge the financial support from the National Science Foundation, Polymers Program, under Grant No. DMR 0513010.