| Thin films exist in different forms, as a single component or mixture of different phases. They can be used in many applications such as adhesives, coatings, lubricants, and displays. When these thin films are confined between surfaces and sheared, they can exhibit interesting properties that are related to the physical, chemical, and geometrical properties of the confining surfaces, the films' intrinsic properties, and the environment that the films are exposed to. During confinement and shear of thin films, it is possible to measure properties that give insight into the structural (mechanical), chemical, optical, and/or electrical properties or activity of the films in response to the applied stresses. These insights can be relevant when considering processing of or developing new applications for these films.; I have focused on understanding the mechanical properties of thin films of nanometer thickness. I have also been interested in how confinement and shear affects the optical absorbance of and charge transfer between thin films. Specifically, I have used the Surface Forces Apparatus to study (1) both normal and shear forces between mica surfaces confining aqueous rhodamine B solutions, (2) the shear forces between mica surfaces coated with dissimilar metal layers protected with self-assembled monolayers, and (3) the normal forces between mica surfaces confining surfactant-coated semiconductor nanoparticles in hydrocarbon solvents.; In the aqueous rhodamine B dye solutions studies, I determined that a concentration gradient exists in the gap between the mica surfaces with a buildup of rhodamine B at the surfaces. Normal and shear forces induced changes in the absorption spectra, indicating a change in molecular alignment, and rhodamine-rhodamine and rhodamine-surface interactions.; I also measured shear-induced charge transfer across dissimilar metal surfaces coated with self-assembled monolayers. The charge transferred and the behavior of the current between the surfaces depended on the applied pressure between the surfaces.; Finally, I measured the forces between surfaces confining surfactant-coated nanoparticles in hydrocarbon solvents. I found that the presence of trace amounts of water had a significant effect on the forces between the surfaces which was caused by the interactions of the water molecules with the surfactant coatings. |
