Solution properties of cationic hydrophobically-modified hydroxyethyl cellulose ethers.

摘要

This doctoral thesis has investigated various aspects of the solution properties of water-soluble amphiphilic polymers. The ultimate goal was to achieve a better understanding of the macroscopic phenomena demonstrated by these systems by elucidating the molecular interactions causing them. Two commercial cationic cellulose ethers were studied, the cationic derivative of hydroxyethyl cellulose, HEC-N+CH₃ and its hydrophobically-modified analogue, HEC-N+C₁₂. Their interpolymeric associations and their interactions with surfactants were studied using photophysical techniques, such as UV-vis and fluorescence spectroscopy.; Initial fluorescence probe experiments were directed at investigating the interactions between these cationic polymers and a series of cationic surfactants. No interaction was predicted to occur in systems where the polymer and surfactant were of the same charge due to electrostatic repulsions. However, the results obtained clearly indicated that polymer/surfactant complexes formed if the polymer contained hydrophobic groups. A more detailed picture of the interactions was then obtained by using polymers to which the dye was covalently attached via an ether linkage. Various pyrene labelled and naphthalene labelled analogues of the two cellulose ethers were synthesised and characterised by standard methods. The interpolymeric associations of cationic polymer solutions was studied using mixed solutions of naphthalene and pyrene labelled polymers using non-radiative energy transfer experiments. Fluorescence studies of these labelled polymers in the presence of cationic surfactants confirmed the results of the probe studies. Other fluorescence studies investigated the interactions of the pyrene labelled HEC-N+C₁₂ with a series of anionic surfactants. A stronger interaction was observed due to the electrostatic attraction of the two species. Additionally, an unexpected feature of the fluorescence spectra led to the speculation of the presence of two possible labelling sites on HEC-N+C₁₂. Fluorescence quenching experiments confirmed this hypothesis.; To study the microenvironment around each site, specifically pyrene labelled cationic hydrophobically-modified hydroxyethyl cellulose ethers were prepared and characterised. An analogous series of naphthalene labelled polymers were prepared for investigations of the interpolymeric associations of polymers of like charge using mixed naphthalene and pyrene labelled polymer solutions. Other investigations of these polymers include studying how the site of hydrophobic modification affects the solution properties of the polymer and the interactions of mixed polymer/surfactant systems.; The interactions that occur simultaneously at the air/water interface have been studied briefly for example in the investigations of the relationship between the interfacial composition and the interfacial viscoelastic behaviour and the foaming properties of polymer/surfactant systems. It was found that in a critical surfactant concentration region, interaction occurs between polymers and surfactants of opposite charge at the air/water interface. This surface flow behaviour was more prevalent in systems where the polymer was also hydrophobically-modified. Dynamic surface tension experiments were conducted to investigate the surface behaviour of dilute aqueous solutions of these cellulosic polyelectrolytes.