Rheological changes at the air-liquid interface and examining different kind of magnetic needles
The main objective in this work was to learn how the instrument, the Interfacial Shear
Rheometer (ISR400), worked and to investigate how the rheological properties, storage
modulus (elasticity), G' and loss modulus (viscous), G'', changes when the surface
pressure at the air-liquid interphase changes. The second objective were to examine the
different kind of magnetic needles used in the experiments and to conclude which type of
needle is best for its specific field of analysis.
It was concluded that the relative heavy needle with mass 70.6 mg and length 50 mm
was best for systems where the viscous and elastic components are significantly large,
where the inertia of the needle is not dominant. It also worked of using the heavier needle
for a system of phospholipids.
For the hydroxystearic acid (HSA) experiment that were tested on NaCl sub-phase there
was a clear improvement after switching from the heavy needle (mass 41.5 mg; length 51
mm) to the relative lighter needle (mass 6.94 mg; length 34.7 mm). The values for the
dynamic modulus therefore had a better agreement with reference literature.
A spread layer of class II hydrophobins (HFBII) could be compressed to a surface
pressure of 46 mNm-1. The G' and G'' values from the frequency sweep were discarded
because the monolayer turned into a very viscous-like liquid, and the oscillating needle,
after compression, was kind of stuck in the sub-phase and moved very staggering during
a frequency sweep.
The needle comparison experiment with silica particles 10 wt% Bindzil CC30 (BCC30),
at pH 3.5 was done to see if there was any difference in the sensitivity for the needles at
the interface which consisted of a pure 10 mM NaCl solution or a 10 mM NaCl solution
with BCC30 added to it. The differences were negligible in terms of surface tension but
there was a clear difference between the heavy needle and the light needle, when
oscillating at higher frequencies (>≈6 rad/s).
With this study, the understanding of ISR400 has increased largely. Several issues have
been addressed and the results provide a good basis for further studies within the many
areas the instrument can be used for. Despite the project's time limit, and the fact that the
instrument was new and untested where the project was carried out, focus areas were
prioritized so good results could be achieved within reasonable goals.
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