Rheological changes at the air-liquid interface and examining different kind of magnetic needles

University essay from Karlstads universitet/Avdelningen för kemiteknik

Abstract:

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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