Title:
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Polymer brushes on charged surfaces : synthesis, characterisation and interactions
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Polymer brushes anchored to surfaces offer an effective route to modification
of interfacial properties such as propensity to fouling , friction mediation and
wetting. However, direct physical measurements of such systems, facilitating
the refinement of polymer brush growth and comparison against polymer
brush theories, remain limited despite considerable research efforts in this
area. This thesis describes an investigation on normal and lateral forces between
surfaces bearing a polY(2-(methacryloyloxy)ethyl}dimethyl-(3-sulfopropyl)ammonium
hydroxide), P(SBMA), brush grafted from a novel two dimensional
cationic macroinitiator using a surface force apparatus, SFA.
Preceding such results this thesis first details the design principles, synthesis
and characterisation of a two dimensional cationic macroinitiator
facilitating the grafting of polymers from mica and silicon substrates. From
this, several polymers were successfully grafted on both mica and silicon.
Normal force measurements are then reported in an aqueous environment
as well as Na(N03) and Ca(N03)2 salt solutions in addition to solutions
composed of water and an ionic liquid, l-hexyl-3-methylimidazolium chloride.
These results show the presence of salts altering brush swelling and solvent
tenacity, manifesting as changes in measured brush thickness and the force
required to deform such a brush layer. Observation of friction mediated by
the polymer brush systems was also made with sliding as well as stick-slip
behaviours seen for P(SBMA) systems in Ca(N03)2 salt solutions.
Finally, the thermal response for ethylene glycol methyl ether methacrylate
polymer brushes anchored to polystyrene particles was investigated. Results
gathered for this system show that the presence of a dynamic monomer
density along the length of a polymer chain gave rise to a complex interplay
of forces. This complex relationship exhibited a marked difference in brush
response compared to similar systems grafted from flat surfaces.
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