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LAOS for thixotropy
1. Large amplitude oscillatory shear (LAOS) on thixotropic materials Speaker: Sun, Weixiang Advisor: Prof. Tong, Zhen Research Institute of Materials Science, South China University of Technology, Guangzhou (510641), P. R. China
9. The structure of Laponite gel charged discs suspension in water House of Cards a synthetic hectorite, [Mg 5.34 Li 0.66 Si 8 O 20 (OH) 4 ]Na 0.66 Layer size: 30 nm in diameter & 1 nm in thickness t w
16. ARES in our lab ARES RFS Transducers: 20g & 1K FRT Software: TA Orchestrator 7.2.1, “Arbitrary Waveshape Tests”.
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18. LAOS of time stable gel The windows for MAOS is small. Laponite 2.0 wt% NaCl 5.0 mM Fourier transform rheology:
19. LAOS of time stable gel Laponite 2.0 wt% NaCl 5.0 mM Fourier transform rheology: Plateau values
20. LAOS of time stable gel MCT prediction Fourier transform rheology: J. M. Brader et al. Phys. Rev. E , 2010, 82 , 061401. Plateau values
21. LAOS of time stable gel Fourier transform rheology: Laponite 2.0 wt% Varying NaCl concentrations Effect of salt concentration γ 0 = 500%
22. LAOS of time stable gel Fourier transform rheology: Styrene-BA particle suspension Effect of salt concentration S. Kallus et al. Rheol. Acta , 2001, 40 , 552-559.
23. LAOS of time stable gel Fourier transform rheology: Laponite 2.0 wt% NaCl 6.0 mM Maxima in higher harmonics.
24. LAOS of time stable gel Fourier transform rheology: Maxima in higher harmonics. V. Carrier and G. Petekidis, J. Rheol. , 2009, 53 , 245-273. 1 Hz 10 Hz Occurs at increasing ω I 3/1 I 5/1 I 7/1 % PS@PNIPAM suspension
25. LAOS of time stable gel Fourier transform rheology: Maxima in higher harmonics. Occurs at decreasing particle concentrations I 3/1 (%) V. Carrier and G. Petekidis, J. Rheol. , 2009, 53 , 245-273. PS@PNIPAM suspension φ v ↑
26. LAOS of time stable gel γ 0 = 5 % γ 0 = 250 % The gel is turned into viscous fluids under LAOS. Lissajous figures: Laponite 2 wt% NaCl 5 mM
27. LAOS of time stable gel Lissajous figure parameters: The proposed parameters reproduce the trend of the fundamental harmonic. G M G L
28. LAOS of time stable gel Lissajous figure parameters: All but the fundamental harmonics are extracted. W. Sun et al. , Polymer , 2011, 52 , 1402-1409.
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30. LAOS of time stable gel Problems in current method of obtaining G L , G M , etc.: Software: MITlaos It uses the Fourier transformed results to calculate G M , etc. Based on a limited number of harmonics
33. Time-variant viscoelastic materials G ( t ; t w ) Fourier transform G * ( ω ; t w ) Shortest time of data acquisition: one cycle (2 π / ω ).
34. Dealing with time-variant viscoelasticity Traditional frequency sweep: t w G * ( ω ; t w ) … ω t w1 t w2 t w3 Not fast enough
35. Dealing with time-variant viscoelasticity E. E. Holly et al. J. Non-Newtonian Fluid Mech. , 1988, 27 , 17-26. Multiwave method – valid only under linear viscoelastic condition. O ( ω min -1 ) << O ( t w )
36. Dealing with time-variant viscoelasticity J. C. Scanlan et al. Macromolecules , 1991, 24 , 47-54. O ( ω min -1 ) << O ( t w ) t w ω Dynamic frequency sweep direction Continuous frequency sweep: Data interpolation t w1 t w2 t w3 ω G * ( ω ) ω G * ( ω ) ω G * ( ω )
37. Dealing with time-variant viscoelasticity t w Δ t > 2 π / ω (one cycle) O ( ω min -1 ) << O ( t w ) Repeated time sweep:
38. Dealing with time-variant viscoelasticity Repeated time sweep: ω ↑ The phenomena should be exactly repeated at each ω . O ( ω min -1 ) << O ( t w ) A. S. Negi and C. O. Osuji, Phys. Rev. E , 2010, 82 , 031404. Laponite gelation
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40. LAOS time sweep of Laponite gel Aging occurs at large strains γ 0 = 1 ~ 20% ω = 5.0 rad/s Laponite 2.0 wt% NaCl 6.0 mM
41. LAOS time sweep of Laponite gel Yielding occurs earlier at larger strains Laponite 2.0 wt% NaCl 6.0 mM γ 0 = 1 ~ 20% ω = 5.0 rad/s
42. LAOS time sweep of Laponite gel Laponite 2.0 wt% Varying NaCl concentrations Times and strains of G’ , G’’ crossover:
43. LAOS time sweep of Laponite gel What about the higher harmonics? The NonLinMon parameter in Orchestrator is I 3/1 . γ 0 = 1 ~ 20% ω = 5.0 rad/s
44. LAOS time sweep of Laponite gel What about the higher harmonics? The Arbitrary Waveshape Test of Orchestrator is not optimized for prolonged tests.
