Controlling out-of-equilibrium phase transitions in complex surfactant systems
File(s)
Author(s)
Donina, Liva
Type
Thesis
Abstract
Surfactants in solutions self-assemble in a range of structures that are academically
and industrially important. In particular, liquid crystalline phases have energies near
kBT and are generally responsive to external fields, including shear flows and small
temperature changes. Lyotropic lamellar Lα phases can undergo a transformation into
multilamellar vesicles (MLVs), which have wide ranging application in protocell models
and particle encapsulants. The Lα-to-MLV transformation exhibits a rich behaviour
when co-surfactant and salt is introduced to the system, and thermal energy provided,
ranging from vesicle formation to shear-controlled hexagonal vesicle packing. In this
thesis, I select sodium dodecyl sulfate (SDS)/octanol/brine (20 g/L NaCl in H2O) as a
model system to investigate the equilibrium and non-equilibrium structures attainable
by these state and process variables, employing continuous and oscillatory microfluidic
flows. Chapter 1 provides an overview of the Lα-to-MLV transformation in non-ionic
and charged surfactant systems and reviews the microfluidic approaches employed in
flow-induced transformations. Chapter 2 introduces the experimental techniques used in
this work, namely polarised optical microscopy (POM), small angle neutron scattering
(SANS), nuclear magnetic resonance (NMR) alongside microdevice design and integration
with SANS. Our research sought to answer the following three questions: 1) what are
the accessible SDS/octanol/brine solution microstructures? 2) what effect the membrane
elastic properties have on the flow induced textures in linear flows? 3) what effect the
microfludic flow field has on SDS/octanol/brine flow induced textures. In Chapter 3, I
investigate the solution structure of SDS/octanol/brine system across the lamellar (Lα),
vesicle (L4) and micellar (L1) phases employing small angle neutron scattering (SANS),
optical microscopy and nuclear magnetic resonance (NMR). Chapter 4 quantifies the
effect of Lα elastic properties on the shear induced Lα-to-MLV transformation by utilising
continuous flow microfluidics on a long serpentine chip. Chapter 5 focuses on the effect of
continuous and oscillatory microfluidic contraction-expansion flows on the formation of
MLVs. Chapter 6 describes an outreach activity at the intersection of surfactant science
and art, first developed for the Great Exhibition Road Festival 2022 and refined since.
The final chapter reflects on the key findings of this PhD project and provides an outlook
for future research.
and industrially important. In particular, liquid crystalline phases have energies near
kBT and are generally responsive to external fields, including shear flows and small
temperature changes. Lyotropic lamellar Lα phases can undergo a transformation into
multilamellar vesicles (MLVs), which have wide ranging application in protocell models
and particle encapsulants. The Lα-to-MLV transformation exhibits a rich behaviour
when co-surfactant and salt is introduced to the system, and thermal energy provided,
ranging from vesicle formation to shear-controlled hexagonal vesicle packing. In this
thesis, I select sodium dodecyl sulfate (SDS)/octanol/brine (20 g/L NaCl in H2O) as a
model system to investigate the equilibrium and non-equilibrium structures attainable
by these state and process variables, employing continuous and oscillatory microfluidic
flows. Chapter 1 provides an overview of the Lα-to-MLV transformation in non-ionic
and charged surfactant systems and reviews the microfluidic approaches employed in
flow-induced transformations. Chapter 2 introduces the experimental techniques used in
this work, namely polarised optical microscopy (POM), small angle neutron scattering
(SANS), nuclear magnetic resonance (NMR) alongside microdevice design and integration
with SANS. Our research sought to answer the following three questions: 1) what are
the accessible SDS/octanol/brine solution microstructures? 2) what effect the membrane
elastic properties have on the flow induced textures in linear flows? 3) what effect the
microfludic flow field has on SDS/octanol/brine flow induced textures. In Chapter 3, I
investigate the solution structure of SDS/octanol/brine system across the lamellar (Lα),
vesicle (L4) and micellar (L1) phases employing small angle neutron scattering (SANS),
optical microscopy and nuclear magnetic resonance (NMR). Chapter 4 quantifies the
effect of Lα elastic properties on the shear induced Lα-to-MLV transformation by utilising
continuous flow microfluidics on a long serpentine chip. Chapter 5 focuses on the effect of
continuous and oscillatory microfluidic contraction-expansion flows on the formation of
MLVs. Chapter 6 describes an outreach activity at the intersection of surfactant science
and art, first developed for the Great Exhibition Road Festival 2022 and refined since.
The final chapter reflects on the key findings of this PhD project and provides an outlook
for future research.
Version
Open Access
Date Issued
2023-04
Date Awarded
2023-10
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Cabral, Joao
Publisher Department
Chemical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)