A Simple Analysis Method to Predict the Large Amplitude Oscillatory Shear (LAOS) Flow Behavior of Viscoelastic Polymer Liquids

A large amplitude oscillatory shear (LAOS) flow has been proved to be an effective tool for characterizing the nonlinear viscoelasticity of complex fluids [1,2], because the Weissenberg number and the Deborah number can be varied independently [3]. In the dynamic viscoelastic behavior of polymeric liquids, the first report on this topic was published by Philippoff in the middle of 1950’s [4]. After Philippoff, numerous studies on the nonlinear behavior have been carried out theoretically and experimentally for a wide variety of materials including polymer solutions [5−8], polymer melts [9,10], suspensions [11−13], emulsions [14,15] and gels [16−20]. During the past several decades, experimental methods called strain-sweep test and sinusoidal waveform test have generally been used to investigate the LAOS behavior of complex materials. In strain-sweep test, a sinusoidal deformation (strain) is applied to a viscoelastic material at a fixed angular frequency and the strain amplitude is increased successively. Dynamic viscoelastic functions including storage modulus and dynamic viscosity are obtained from this test. One of the most important another reasons to perform strain-sweep test is to determine the strain limits of linear viscoelastic response prior to conducting other rheological measurements such as frequency-sweep test, creep and stress relaxation test [21,22]. On the other hand, a periodic strain is imposed to a viscoelastic material at an arbitrary angular frequency and strain amplitude in sinusoidal waveform test. The sinusoidal stress waveform is detected with time as the material’s response. Corresponding Author: Ki-Won Song E-mail: kwsong@pusan.ac.kr