Development of a mechanism-based correlation model to predict the effects of freezing and thawing on the stability of vesicular Dispersions
File(s)
Author(s)
Francis, Sharanda
Type
Thesis
Abstract
The phase behaviour of aqueous dioctadecyl dimethylammonium chloride (DODAC) solutions were studied to model the stability of liquid fabric enhancers, when exposed to the environmental stresses of cooler climate regions during transportation or storage. These effects were studied using; SAXS and WAXS, 1H NMR, DOSY and polarised light microscopy, before and after freeze-thawing (FT) of the DODAC bilayers.
The effects upon FT resulted in a FT induced swelling, where the magnitude of this swelling decreased with the addition of CaCl2 to the aqueous DODAC solution. Additionally, in the absence of CaCl2, the cooling properties of the bilayers resulted in a temperature shift of the Lα->Lβ’ transition from ~31 to ~35 oC after FT, instead of the two transitions given at ~31 and ~35 oC in the presence of CaCl2 after FT. This suggests that CaCl2 decreases the changes to the DODAC bilayers and properties, upon FT.
The DODAC aqueous solution is studied for the addition of glycerol and an ethoxylated alcohol surfactant. Glycerol caused swelling of the DODAC bilayers and the ethoxylated alcohol surfactant caused a lateral phase separation of a spherical to planar bilayers transition. These alterations to the DODAC bilayers, minimised the differences between the bilayers before and after FT. Also, it was shown that small unilamellar vesicles promoted the Lα->Lβ’ transition temperature shift from ~31 to ~35 oC and a spherical->planar bilayers transition, after FT.
The freezing behaviour of the DODAC bilayers were observed as a cooling induced dehydration which took place after the Lα->Lβ’ phase transition instead of ice formation in the bulk water phase, at high pressure and low temperature. This resulted in a metastable freezing state with tilted bilayers, at ~ -2.0 oC which did not lead to a transition into the Lc phase until incubation at -18 oC. The effects upon thawing showed a lack of osmotic responsiveness between -5.0 and 15 oC, and an influx of water at 20 oC resulted in greater swelling of the DODAC bilayers than before FT.
The effects upon FT resulted in a FT induced swelling, where the magnitude of this swelling decreased with the addition of CaCl2 to the aqueous DODAC solution. Additionally, in the absence of CaCl2, the cooling properties of the bilayers resulted in a temperature shift of the Lα->Lβ’ transition from ~31 to ~35 oC after FT, instead of the two transitions given at ~31 and ~35 oC in the presence of CaCl2 after FT. This suggests that CaCl2 decreases the changes to the DODAC bilayers and properties, upon FT.
The DODAC aqueous solution is studied for the addition of glycerol and an ethoxylated alcohol surfactant. Glycerol caused swelling of the DODAC bilayers and the ethoxylated alcohol surfactant caused a lateral phase separation of a spherical to planar bilayers transition. These alterations to the DODAC bilayers, minimised the differences between the bilayers before and after FT. Also, it was shown that small unilamellar vesicles promoted the Lα->Lβ’ transition temperature shift from ~31 to ~35 oC and a spherical->planar bilayers transition, after FT.
The freezing behaviour of the DODAC bilayers were observed as a cooling induced dehydration which took place after the Lα->Lβ’ phase transition instead of ice formation in the bulk water phase, at high pressure and low temperature. This resulted in a metastable freezing state with tilted bilayers, at ~ -2.0 oC which did not lead to a transition into the Lc phase until incubation at -18 oC. The effects upon thawing showed a lack of osmotic responsiveness between -5.0 and 15 oC, and an influx of water at 20 oC resulted in greater swelling of the DODAC bilayers than before FT.
Version
Open Access
Date Issued
2018-10
Date Awarded
2019-11
Copyright Statement
Creative Commons Attribution Licence
License URL
Advisor
Ces, Oscar
Law, Robert
Brooks, Nicholas
Seddon, John
Cabral, Joao
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)