Poly(N-isopropylacrylamide) (PNIPAM) belongs to a class of stimuli-responsive materials known as “smart” polymers. When cast in the form of a hydrogel, PNIPAM’s lower critical solution temperature (LCST) of 32°C serves as a threshold for volumetric change. For solution temperatures below LCST, PNIPAM hydrogels exist as swollen, hydrophilic networks of polymer and water, spontaneously expelling the bound water molecules to shrink (and become increasingly hydrophobic) as temperature increases beyond LCST. This thesis centers on PNIPAM hydrogel layers grafted along the inner diameter of glass capillaries in order to form a temperature-responsive gating mechanism that spontaneously seals for solution temperatures below LCST. Surprisingly, very thin layers (10-20µm) of PNIPAM have dramatic effects on bulk fluid flow through the capillary due to complex interactions at the swelling interface. Specifically, for the case of capillary pressure driven flow, the swelling PNIPAM interface gives rise to "stick-and-slip" motion for bulk flow. Experiments explore the extent of this phenomenon, while a theoretical framework is proposed to model how the evolving gel interface pins the contact line. Additionally, an exploratory segment of this work examines the ways in which PNIPAM hydrogel nanoarrays can be synthesized via scalable template methods. Nanostructured PNIPAM films exhibit dramatic changes in surface properties with temperature, characterized by very low contact angles (~10°) below LCST, and very high ones (~160°) above LCST. Results for several methods are presented with lessons learned to guide future development of surfaces with temperature-responsive wetting properties.

Contact fatigue damages resulting either from static or dynamic contact are of interest for understanding the failure modes and mechanisms leading to improvement of the components’ performances in tribological applications. The objective of this research was to ascertain how and to what extent the counterface materials, loading conditions, contact configuration, lubrication, and the environment affect the failure behaviours of material under static and dynamic contact fatigue loading. An experimental ball-on-flat test configuration was employed for both static and dynamic contact fatigue testing. In house designed test rig was used to study static cyclic loading contact fatigue behaviours of brittle polymethylmethacrylate (PMMA) in contact with balls made of different materials, i.e. Si3N4, steel, aluminium, bronze and PMMA in dry and oil-lubricated conditions. A modified four ball test machine was used to study dynamic rolling contact fatigue behaviours of thermally sprayed molybdenum and titanium coatings in contact with steel balls in dry and seawater conditions. The static contact fatigue and the dynamic contact fatigue test results revealed that counterface material, loading magnitude, lubricant and the environment play a vital role in controlling failure modes and the extent of damage. In static contact fatigue, adhesive strength of the interface was the key factor controlling damage of the PMMA plate in both dry and oil-lubricated conditions. In dry conditions, three failure modes, i.e. adhesive wear, ring cracks, and radial cracks controlled the damage of PMMA to a different degree for each combination of materials. Whereas, the damage of each combination in oil-lubricated conditions was affected by the extent of three failure modes, i.e. adhesive wear, radial cracks and abrasive wear. In dynamic contact fatigue tests, adhesive wear and inter-lamellar cracking were the major failure modes controlling damage of molybdenum coating and titanium coating in dry contact conditions while abrasive wear, corrosion and lubrication controlled damage processes in seawater conditions.