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Title: The colour change and microstructure evolution of wet flowing paint when subject of shear
Author: Chen, Y. K.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2001
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This thesis is concerned with the colour change and microstructural evolution of wet paint when subject of shear. When different processing shear histories are applied to certain paints, the resulting colour of the paint can vary. Paint consists of pigment particles suspended in a mixture of resin and solvent, and this multi-phase structure results in a complex microstructure. For this reason there can be many possible causes of this colour change, one of which was thought to relate to the organisation of the pigment dispersion. Rheological measurements of paint were carried out to investigate whether there was a link between rheology and colour change. The measurements were performed using a Rheometrics Dynamic Spectrometer (RDS II) at low shear rates and a Multi-Pass Rheometer (MPR) at high shear rates. Although the shear ranges of the RDS II and MPR did not overlap, extrapolation of data obtained at low shear rates matched those from the MPR at high shear rates. The rheological response of the material was described using a viscoelastic K-BKZ integral constitutive equation in combination with a Wagner damping factor. Systematic tests under controlled conditions were successfully performed, and the results of three paint samples were compared. The experimental findings indicated that the observed colour change behaviour of paint was related to the modification of size and size distribution of pigment agglomerates, both during and after shear. In order to correlate pigment size with the resulting paint colour, an attempt was made to model these experimental findings. A mathematical model was developed on the basis of the Mie scattering theory. This model was verified by a case study, and its prediction gave semi-quantitative agreement with the experimental findings.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available