| dc.description.abstract | Nanoscale polymer films have numerous potential applications such as protective
coatings, flexible electronics, energy harvesting devices, and drug delivery systems. For
realization of these potential applications, the mechanical properties of these materials and
the underlying physics need to be understood.
This dissertation focuses on understanding the responses of nanoscale films to mechanical
deformations. In this regard, an elastic instability was exploited to locally bend
and impart a local tensile stress in a nanoscale polystyrene film, and directly measure the
resulting residual stress caused by the bending. Our results indicate that the onset of permanent
deformation for thin polystyrene films is an order of magnitude smaller than what has
been reported for the bulk value. In addition, not only is the onset of failure strain found to
be small but also it increases with increased confinement. Using similar processing techniques,
the yield strain of a more complex material - poly(styrene-b-divinylpyridine) - was
studied. Similar to the polystyrene films, failure in polystyrene-b-poly(2-vinylpyridine) is
also initiated at extremely low strain and is influenced by thin film confinement effects. In
addition, we have demonstrated that internal nanostructure of self-assembled polystyreneb-
poly(2-vinylpyridine) affects the onset of failure strain.
Having introduced an idealized heterogeneity to a sample through ultraviolet/ozone
treatment, we have created samples ranging from continuous thin films to sets of isolated
plates. We demonstrated that, when subjected to mechanical deformation, the unbounded
plates form isotropic undulations that persist even beyond high strain. In contrast, isolated
plates undergo non-isotropic undulations in the range of high strains. The non-isotropic
undulation shape has been described through a simple numerical modeling subjected to
controlled boundary conditions. The agreement between experiment and numerical modeling
is remarkable. Finally, through an integrated experimental methods and theoretical modeling, the
response of discrete colloidal layers to mechanical deformations have been exploited. The
buckling profiles measured experimentally demonstrate a great insight that the continuum
model may not be able to predict the response of discrete systems. Theoretically, a granular
model was constructed and structural stability analysis was investigated to predict the
experimental observations. The overall agreement of the experiment and the modeling was
good. | en_US |
