Crystallisation of sodium dodecyl sulfate in water micellar solutions: effect of temperature profiles, flow and additives
File(s)
Author(s)
Miller, Ruhina Mariam
Type
Thesis or dissertation
Abstract
Stability determination of formulated products represents an ongoing challenge. These solutions have complex energy landscapes and experience a wide variety of conditions during manufacturing, transportation, storage and use. The mesostructure of such multicomponent mixtures is sensitive to external influences and time, which affects their performance in real-life applications. Understanding product metastability, in particular phase transitions such as crystallisation, is important both academically and practically. Current methods of stability determination are often time consuming and do not provide the causes of such phase changes.
Here this challenge is addressed by focusing on a ubiquitous surfactant system: sodium dodecyl sulfate in water micellar solutions. A fundamental understanding of the system’s crystallisation kinetics was obtained by developing and implementing a range of experimental and analytical techniques. Three different approaches were employed – the effects of both isothermal and linear temperature profiles were initially examined, before assessing the impact of various additives under both isothermal and linear cooling conditions. Lastly the consequence of different flow rates and flow types using microfluidics, including straight channel flow, oscillatory and push-pull, was examined and quantified.
For the temperature profiles both an increase in isothermal hold temperature and lower cooling rates were found to decrease the rates of crystallisation, with the linear cooling data mapped onto the isothermal results. A wide variety of morphologies formed across the investigative window, which could be classified as the mono- and hemihydrate polymorphs. Additives with structures comparable to SDS were found to have potent effects on the crystallisation kinetics and morphologies of SDS even at the lowest concentrations, with their mode of action deemed to be kinetic rather than thermodynamic. Lastly, crystallisation in microfluidic devices was found to be sensitive to device type, temperature control and flow profiles. Overall this project has resulted in three first-author and two other publications.
Here this challenge is addressed by focusing on a ubiquitous surfactant system: sodium dodecyl sulfate in water micellar solutions. A fundamental understanding of the system’s crystallisation kinetics was obtained by developing and implementing a range of experimental and analytical techniques. Three different approaches were employed – the effects of both isothermal and linear temperature profiles were initially examined, before assessing the impact of various additives under both isothermal and linear cooling conditions. Lastly the consequence of different flow rates and flow types using microfluidics, including straight channel flow, oscillatory and push-pull, was examined and quantified.
For the temperature profiles both an increase in isothermal hold temperature and lower cooling rates were found to decrease the rates of crystallisation, with the linear cooling data mapped onto the isothermal results. A wide variety of morphologies formed across the investigative window, which could be classified as the mono- and hemihydrate polymorphs. Additives with structures comparable to SDS were found to have potent effects on the crystallisation kinetics and morphologies of SDS even at the lowest concentrations, with their mode of action deemed to be kinetic rather than thermodynamic. Lastly, crystallisation in microfluidic devices was found to be sensitive to device type, temperature control and flow profiles. Overall this project has resulted in three first-author and two other publications.
Version
Open Access
Date Issued
2018-09
Date Awarded
2018-12
Copyright Statement
Creative Commons Attribution NonCommercial Licence
Advisor
Ces, Oscar
Cabral, Joao
Brooks, Nick
Sponsor
Engineering and Physical Sciences Research Council
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)