User:Andrew Sun/Notebook/LAOS study on physical gelation/2009/05/04

LAOS Study on Physical Gelation

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LAOS Experiment on PAAc/Fe(III) Gels Objectives To approach the critical gelling point Samples Gels from 5 wt% PAAc solution (Mv=51100): f=1.73e-3 f=2.30e-3 (f=[Fe(III)]/[COOH]) Instruments TA ARES Rheometer Results Decrease of τ0 Fig. 1 During LAOS experiments of sample f=0.0173, the stress amplitudes τ0 started to decrease with time after the run Arby Wave (5). Frequency sweep before and after the LAOS experiment (Fig. 1) indicates that the gel had gradually dissociated in to a critical gel, with coinciding G′ and G′′. Fig. 2 Sample f=0.0230 showed less dissociation, as shown in frequency sweep experiment before and after LAOS experiment (Fig. 2). The dissociation of sample f=0.0173 was attributed to exposed Cu surface after the silicon oil gradually dissolved the correction pen cover. In experiment of sample f=0.0230 more correction pen cover was applied. FT-Rheology Fig. 3 I3/I1 ratios of the two samples were plotted against strains in Fig. 3. In the case of the first sample, the software of the rheometer did not allow strains larger than 1200%. The upper limits of the strain allowed by the software seems to vary according to the gaps. Smaller gaps allows larger strains. From Fig. 3 nothing can be concluded.