Keratins are important structural components of hair and skin. There has been extensive study of keratins from the health and medical perspectives, although little work has been done to date to investigate their basic physicochemical properties in the form of biomaterials. The work presented in this thesis aimed to study surface and interfacial adsorption and solution aggregation of water soluble keratin polypeptides (made available by previous work within the research group). A range of physical techniques were employed including spectroscopic ellipsometry (SE), neutron reflection (NR), dual polarisation interferometry (DPI), quartz crystal microbalance with dissipation (QCM-D), dynamic light scattering (DLS) and small-angle neutron scattering (SANS).A major technical advantage of the neutron techniques is the use of hydrogen/deuterium substitution to enhance structural resolution. This approach was explored to study the interaction of keratins with both conventional surfactants and novel biosurfactants. The work presented comprises four results chapters. The first examines and compares four widely used interfacial techniques, SE, DPI, QCM-D and NR, by studying the adsorption of C12E6 at the silicon oxide/water interface. Whilst the data exhibits a large degree of consistency in the interfacially adsorbed amount, each technique helped reveal unique structural information with a high degree of complementarity. The second results chapter reports on findings regarding the properties of keratin polypeptides in surface adsorption and solution aggregation. It was found that the keratins adsorbed strongly on the surface of water, and formed rugby-shaped nanoaggregates in solution, the size and shape of which responded to salt concentration. The third results chapter reports on the interfacial behaviour of keratin/surfactants complexes in bulk solution, with cationic DTAB and anionic SDS as model conventional surfactants. It was found that both the electrostatic and hydrophobic forces contributed strongly to the surface adsorption processes. The final results chapter reports on interactions of a coated keratin film with novel biosurfactants including rhamnolipids (R1 and R2 with 1 and 2 sugar head(s), respectively) and Mel-C. The keratin films formed were found to be exceptionally stable and reproducible below pH 8, and these films could be widely used as model keratin substrates for screening their binding with surfactants and bioactive molecules. Both rhamnolipids and Mel-C exhibited strong adsorption onto the keratin substrate and interestingly, whilst R1 exhibited a completely reversible adsorption, R2 showed only a partially reversible adsorption. Mel-C showed some degree of irreversible adsorption similar to R2 and exhibited the strongest adsorption at around pH 4-5. These results show mild interactions with the keratin substrate, but indicate that the extent of adsorption and desorption could be manipulated by surfactant structure or solution conditions.The findings presented in this thesis are fundamental in aiding the development of the use of keratin polypeptides as biomaterials, in applications such as personal care. The work is also highly relevant to the understanding of the interactions between surfactants and keratin molecules at interfaces and in solution.
|Date of Award||1 Aug 2016|
- The University of Manchester
|Supervisor||Jian Lu (Supervisor)|
- Neutron reflection
- Small angle neutron scattering