User:Andrew Sun/Notebook/LAOS study on physical gelation/2009/05/07

LAOS study on physical gelation

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LAOS Experiment of PAAc/Fe(III) Gels Objectives Find the critical gel point Samples Gels from 5 wt% PAAc solution (Mv=51100): f=1.30e-3 (f=[Fe(III)]/[COOH]) Instruments ARES Rheometer Results Frequency Sweep Fig. 1 The sample is close to the critical gel point as shown in Fig. 1 1st run. But it underwent an obvious dissociation as indicated by frequency sweeps before and after LAOS experiment (Fig. 1). FT-Rheology Fig. 2 The sample exhibit much larger values of 3rd harmonics compared with sample f=2.30e-3, while the manner I3/1 increases with strain amplitudes are similar, as shown in Fig. 2. LAOS Experiment of PAAc/Fe(III) Gels Objectives Effect of molecular weights Samples Gels from 5 wt% PAAc solution (Mv=22400): f=1.30e-3 Instruments ARES Rheometer Results Frequency Sweep Fig. 3 Frequency sweep result (Fig. 3 1st run) shows that the sample is close to critical gel point. Comparison with frequency sweep after LAOS experiments indicates that the extend of dissociation was minor. FT-Rheology Fig. 4 The nonlinearity of the sample was comparatively obvious. The 3rd harmonic appeared since the strain amplitude exceeded 500% (Fig. 4), and the 5th harmonic appeared at the strain amplitude 1900%. LAOS Experiment of PAAc/Fe(III) Gels Objectives Effect of molecular weights Samples Gels from 5 wt% PAAc solution (unknown molecular weight): f=1.30e-3 Instruments ARES Rheometer Results Frequency Sweep Fig. 5 The sample was below the critical gel point. Dissociation occurred after LAOS experiment. See Fig. 5. FT-Rheology Fig. 6 Fig. 6. LAOS Experiment of PAAc/Fe(III) Gels Objectives Effect of molecular weights Samples Gels from 5 wt% PAAc solution (Mv=22900): f=1.30e-3 Instruments ARES Rheometer Results Frequency Sweep Fig. 7 The sample was below the critical gel point (Fig. 7). FT-Rheology No higher harmonic observed up to strain amplitude of 1900%.