Experimental Studies of Instabilities Near the Sol-Gel Transition
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
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
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
Place, publisher, year, edition, pages
Institutt for fysikk , 2012. , 96 p.
ntnudaim:7197, MTFYMA fysikk og matematikk, Teknisk fysikk
IdentifiersURN: urn:nbn:no:ntnu:diva-18888Local ID: ntnudaim:7197OAI: oai:DiVA.org:ntnu-18888DiVA: diva2:566349
Fossum, Jon Otto, Professor