Discrete Fourier Transform Analysis to Characterize the Large Amplitude Oscillatory Shear (LAOS) Flow Behavior of Viscoelastic Polymer Liquids

서지정보

· 발행기관 : 한국섬유공학회
· 수록지 정보 : 한국섬유공학회지 / 53권 / 5호 / 317 ~ 327페이지
· 저자명 : 장갑식, 안혜진, 송기원

초록

The objective of the present study is to systematically characterize the nonlinear viscoelastic behavior of concentrated polymer systems in large amplitude oscillatory shear (LAOS) flow fields by means of discrete Fourier transform (DFT) analysis. Using an Advanced Rheometric Expansion System (ARES), the dynamic viscoelastic behavior of aqueous poly(ethylene oxide) (PEO) solutions with various molecular weights and different concentrations has been investigated with several fixed strain amplitudes and constant angular frequencies. The nonlinear viscoelastic functions and the degree of nonlinearity were derived from the Fourier spectra of stress responses, and then the nonlinear behavior was interpreted by the use of 3D and contour plots, respectively. The effects of strain amplitude and angular frequency on the nonlinear viscoelastic behavior were nextly discussed in depth. In addition, the strain limits of linear viscoelastic response were determined from the ratio of harmonic contributions, and then the validity of Pipkin diagram with regard to characteristic time was evaluated for all PEO solutions. The main findings obtained from this study are summarized as follows: (1) At small strain amplitudes, the influence of the first harmonic contribution is dominant. As the strain amplitude becomes larger, however, the effect of higher odd harmonic contributions is increased, resulting in an occurrence of a nonlinear viscoelastic behavior. (2) The degree of nonlinearity is increased with an increase in strain amplitude. This is also increased with increasing angular frequency until reaching the maximum value at a certain angular frequency and then decreased with a further increase in angular frequency. (3) The Pipkin diagram with regard to characteristic time is a very effective method to explore the nonlinear regime of viscoelastic polymer liquids in LAOS deformations.

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