Magnetic resonance investigations of phase separation in vesicle-polymer mixtures

Thompson, Emma Sian (2019). Magnetic resonance investigations of phase separation in vesicle-polymer mixtures. University of Birmingham. Ph.D.

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Abstract

Vesicle dispersions are used in consumer products, cosmetics and food. Frequently, non-adsorbing polymer is added to dispersions to enhance properties, such as, dispensibility. Aqueous dispersions of diethylesterdimethyl ammonium chloride (DEEDMAC) vesicles mixed with poly-diallyldimethyl ammonium chloride (poly-DADMAC) were investigated at various vesicle-volume fractions and polymer concentrations. Such vesicle-polymer mixtures are of interest for fabric-enhancing applications, but undergo phase separation, limiting product “shelf-life”. Understanding the effect of poly-DADMAC on vesicle microstructure and rate of phase separation facilitates product formulation. Vesicle-polymer mixtures were investigated using nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI).

NMR measurements showed that the diffusion coefficient and T2 relaxation time of water were reduced by the vesicles and MRI of local T2 and diffusion enabled vesicle-rich and vesicle-poor regions to be identified. Average T2 relaxation times decreased and average diffusion coefficients increased on polymer addition showing vesicle dispersions are osmotically sensitive. T2 maps showed vesicle-poor regions forming in dispersions prior to phase separation. Vesicle-poor regions formed near air bubbles, trapped in the suspension, and near container walls. Formation of these vesicle-poor regions indicated that transient colloidal gels had formed, on polymer addition, due to depletion forces. Vesicle-poor regions were quantified using different image analysis methods. Moran’s I, a measure of spatial-autocorrelation, was the most effective at differentiating images and was used to study the rate of phase separation. The rate of phase separation was found to depend on the gel yield stress, vesicle volume fraction and the number of air bubbles trapped in the dispersion.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):