Although the glass transition temperature (Tg) and dynamics of polymers confined to the nanoscale have been studied for twenty years, a physical understanding is still lacking. The reason for a polymer species dependent Tg-confinement effect and the role of neighboring polymer domains in perturbing the Tg of a confined species are areas with a need for greater study as they will inform many of the decisions regarding the use of polymers in nanomaterials.
In this work, fluorescence spectroscopy is used as the primary tool to characterize Tg in a number of systems. First, micelle core Tg and critical micelle temperatures can be determined via pyrenyl label fluorescence for block copolymers in organic solvent at polymer contents which cannot be reliably characterized by other standard methods. Next, measurements were extended to miscible polymer-polymer blend systems where two component Tgs can be determined via a single pyrene-labeled component. Fluorescence can characterize systems with small component Tg differences and near-infinitely dilute blend components unlike scanning calorimetry.
Studies of the near-infinitely dilute blend components reveal that a 0.1 wt% polystyrene component can have its Tg tuned over a 150 °C range depending on the blend partner. Analogous tunability of Tg is also reported in multilayer film systems with an ultrathin PS layer surrounding by bulk neighboring domains. The same limiting Tg is reported by PS for a given neighbor indicating a common physical origin of perturbations in both systems. The perturbations are correlated with fragility which also tracks with the magnitude of Tg-confinement effects in single layer polymer films. Thus, fragility provides a unifying explanation of confinement effects in multilayer films, blends, and single layer films (in the absence of attractive interactions).
Surface wave dynamics are also examined in ultrathin polystyrene layers on various substrates. It is demonstrated that surface dynamics become much slower than anticipated by capillary wave theory as the film thickness decreases. Additionally, surface wave dynamics become orders of magnitude faster as the modulus of the supporting substrate decrease.
|Advisor:||Torkelson, John M.|
|Commitee:||Broadbelt, Linda J., Burghardt, Wesley R., Shull, Kenneth R.|
|Department:||Chemical and Biological Engineering|
|School Location:||United States -- Illinois|
|Source:||DAI-B 74/09(E), Dissertation Abstracts International|
|Subjects:||Polymer chemistry, High Temperature Physics, Plastics|
|Keywords:||Glass transition temperature, Nanoconfinement, Polymer blends, Surface dynamics, Thin films|
Copyright in each Dissertation and Thesis is retained by the author. All Rights Reserved
The supplemental file or files you are about to download were provided to ProQuest by the author as part of a
dissertation or thesis. The supplemental files are provided "AS IS" without warranty. ProQuest is not responsible for the
content, format or impact on the supplemental file(s) on our system. in some cases, the file type may be unknown or
may be a .exe file. We recommend caution as you open such files.
Copyright of the original materials contained in the supplemental file is retained by the author and your access to the
supplemental files is subject to the ProQuest Terms and Conditions of use.
Depending on the size of the file(s) you are downloading, the system may take some time to download them. Please be