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Experimental Studies of Instabilities Near the Sol-Gel Transition
Norwegian University of Science and Technology, Faculty of Natural Sciences and Technology, Department of Physics.
2012 (English)MasteroppgaveStudent thesis
Abstract [en]

This master thesis presents a new experimental way to dynamically determine rheological properties of a complex fluid. The fluid investigated is a suspension of the synthetic clay mineral laponite of 3 wt%. This is mixed together with distilled water or a NaCl solution with concentrations bellow 10^2 M. Laponite gels are thixotropic and shear thinning with a yield stress. In the experiments done during this thesis the transition between liquid and solid behavior is investigated using a Hele-Shaw cell and a rheometer. Three different phases is observed with respect to waiting time and NaCl concentration. These are recognized as a liquid phase for small concentration of NaCl and short waiting times and a solid phase for high concentration of NaCl and long waiting time. In the intermediate range a viscoelastic phase is observed. Some experiments were done with the sample placed between crossed polarizers, and birefringence was observed in all three phases. In the solid phase it is observed only a small area around the fracture tip. In the liquid phase this is observed in front of the finger, but this is not a stable phase. In the viscoelastic regime a stable nematic phase occur along the stress field around the interface of the bubble. This nematic phase will align normal to the glass surface. Fracture like patterns in the nematic phase are observed. This is an elastic behavior with the clay platelets aligning normal to the stress field to prepare for fractures to propagate there. Different NaCl concentrations will give different arrested states, respectively a repulsive glass and a attractive gel. It is expected that glass and gels behave differently in this experiment, but this was not confirmed. A gel phase have been observed in concentrations of NaCl above 5*10^3 for waiting times up to 605 hours. For smaller concentrations a even longer waiting time is expected and experiments on this needs to be performed in future studies. In addition this experiment could investigate and give insight of flow in complex fluid. To investigate this further, tracer particles have been used in a few experiments. The results are promising for further studies. In this thesis work, a large range in waiting times and concentrations of NaCl have been investigated. In future studies it should be carried out experiments in a smaller range of these parameters along with other parameters. Also a more quantitative analysis should be carried out. Especially the transitions between fluid/viscoelastic and viscoelastic/solid is interesting to investigate further.

Place, publisher, year, edition, pages
Institutt for fysikk , 2012. , 96 p.
Keyword [no]
ntnudaim:7197, MTFYMA fysikk og matematikk, Teknisk fysikk
URN: urn:nbn:no:ntnu:diva-18888Local ID: ntnudaim:7197OAI: diva2:566349
Available from: 2012-11-08 Created: 2012-11-08

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