Structure-self-assembly-function relationships of azobenzene photosurfactants
Citation:
BLAYO, CAMILLE, Structure-self-assembly-function relationships of azobenzene photosurfactants, Trinity College Dublin.School of Chemistry, 2019Download Item:
Abstract:
Self-organisation of individual molecules into supramolecular systems is an attractive approach to design stimuli-responsive materials. This thesis aims to understand and predict the self-assembly behaviour of surfactants containing a photoresponsive azobenzene chromophore. These photosurfactants (PS) are amphiphilic molecules which demonstrate the combined ability to form supramolecular structures above a critical micelle concentration (CMC) and change their properties, such as size and polarity, upon photoisomerization. The goal is to investigate the structure-function relationships in azobenzene photosurfactants (PS) to design new light responsive systems for micellar catalysis and nanotemplating applications.
Chapter 1 introduces key concepts of self-assembly processes, photoisomerisation properties of azobenzenes and recent developments and applications of PS. Chapter 2 provides a theoretical background of the concepts, whilst Chapter 3 gives a detail experimental list of instruments used in this thesis. Chapters 4-6 focus on the design, synthesis and characterisation of a series of cationic azobenzene photosurfactants (AzoTABs) in water and the use of light to modulate the physicochemical properties. The ability to tune the self-assembled nanoscale organisation of AzoTABs is shown by varying the hydrophobic segment of the molecule and the position of the chromophore within the structure. The investigation of the aggregate growth, from dispersed unimers, to micellar assemblies was conducted using a combination of techniques, such as surface tensiometry, dynamic light scattering, small-angle neutron and X-ray scattering. Additionally, light-induced isomerisation was proven to significantly increase the hydrophilicity of the surfactants and to modify the morphology of the micellar aggregates.
Conventional non-responsive surfactants are known to form a variety of lyotropic liquid crystal (LLC) phases. Such supramolecular systems are used as sacrificial templates or matrices to synthesise porous materials. However, cationic azobenzene photosurfactants forming LLC phases have never been reported to date. The results presented in Chapter 6 demonstrate that the careful molecular design of the amphiphilic molecules can promote the formation of LLC phases in AzoTABs. Additionally, the concentration-temperature-structure relationships required to access desirable LLC phases have been identified and the stability of these mesophases has been investigated as a function of temperature and photoisomerisation.
The current need to identify new paths towards the sustainable synthesis of complex organic molecules has driven chemists to use water as a solvent. Micellar catalysis is an elegant way to perform traditional organic reactions using the self-assembly of surfactants as nanoreactors. In Chapter 7, cationic azobenzene photosurfactants in micellar conditions have been investigated to catalyse an aldol condensation reaction in water. The self-assembly-structure-efficiency of the catalyst was studied as a function of concentration and temperature. The effect of photoisomerisation on the efficiency of the catalysis was also studied. Finally, the ability to recycle the solution of micelles to perform several cycles of catalysis is discussed.
This thesis demonstrates that the molecular design of cationic azobenzene photosurfactants drives the self-organisation towards ordered structures. These structures can be rationalised and predicted based on the molecular design of the starting photosurfactant. The self-assembly process is a dynamic event that can be modified by subtle changes of easily controllable external parameters, such as concentration, temperature and photoresponse. The knowledge gathered in this thesis on the structure-property relationships in AzoTABs will be crucial to design new light-responsive surfactants with targeted properties for their intended applications.
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TCD
Description:
APPROVED
Author: BLAYO, CAMILLE
Advisor:
Dunne, PeterPublisher:
Trinity College Dublin. School of Chemistry. Discipline of ChemistryType of material:
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Full text availableKeywords:
Light responsive materials, Photosurfactants, Self assemblyLicences: