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Title: A study of the alignment of polymeric molecules and vesicles in fluid flows for linear dichroism experiments
Author: Amarasinghe, Don Praveen
ISNI:       0000 0004 7425 6412
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2018
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Linear dichroism (LD) spectroscopy is a technique which uses polarised light to make inferences on the relative orientations of chemical groups within a molecule. A requirement for experiments using this technique is the alignment of molecules in the analyte. This thesis considers the use of fluid flows to align molecules. The use of bead-spring and bead-rod models to simulate the behaviour of polymers and particles in fluid flows has been extensively discussed in the literature. In this work, the FENE-Fraenkel spring force law is implemented in bead-spring chain simulations, to assess the alignment behaviour of molecules in flow. Analytical properties of FENE-Fraenkel springs are derived and used to inform the coding of the simulation programme and to assess its outputs. The results of these simulations were comparable to both analytical results in zero-shear conditions and to data previously published by Hsieh et al. [48] on bead-spring chains in extensional flow, albeit with a reduced signal-to-noise ratio. Simulations of the alignment of FENE-Fraenkel spring dumbbells in shear flows show increased alignment with high shear rates, similar to modelling data published by McLachlan et al. [89]. This work also considers the use of microfluidic devices manufactured from polydimethylsiloxane to perform linear dichroism studies on DNA and vesicles in solution. A wide channel and cross-slot device are developed to provide conditions for pressure-driven and extensional flow to align molecules. Both devices are shown to align DNA molecules to measure an LD signal, with the cross-slot performing better than the wide channel device. With solutions of vesicles containing 1,6-Diphenylhexa-1,3,5-triene, a membrane probe, the wide channel device is shown to provide weak vesicle alignment to measure an LD signal. However, both microfluidic devices are unable to align molecules as well as Couette flow, the method normally used to align molecules for LD experiments.
Supervisor: Not available Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry