Use of Rheology to Assess Structures in Polymer Nanocomposites
Abstract
Nano-scale particles due to their outstanding ability to improve physico-mechanical properties of polymeric matrices have been the major research interest in composite science area in recent years. In many cases the so-called improved properties are considered to be linked to the irreversible particle aggregation, leading to formation of fractal clusters which eventually coalesce and constitute a sample-spanning network structure. If not masked by dispersing medium elasticity, self-similar, fractal nanoparticle superstructure imparts solid-like behavior to the long-time response of a wide variety of complex fluids.
The main focus of this PhD dissertation is distinguishing the main parameters affecting particle-particle and polymer-particle interactions and using this knowledge to develop nanocomposites with improved dispersion-states and properties. Nanofillers such as undoped and nitrogen-doped multi-walled carbon nanotubes (MWCNTs) and organically modified clays as well as more recently developed nanofillers such as graphene nanoribbons (GNRs) were employed for this purpose. In this context, the effect of polymer matrix molecular features was also taken in to the account.
Results of this work proved the importance of polymer matrix relaxation time distribution and how it can be used to detect solid-like behavior via rheological technique. It was also demonstrated that linear and nonlinear melt-state rheological responses of nanocomposites would be significantly impacted by nanofiller surface chemistry. Observed differences were explained by the inhomogeneity of surface charge density distribution and suppressed short-range interactions in presence of surface functionalities. As a consequence, short-range interactions become dependent on particle-particle orientation-state leading to significant changes in the dispersion-state and the viscoelastic and thixotropic behavior of the polymer nanocomposites. Geometrical features of nanofillers were also found to play a major role in shaping the solid-like behavior. It was found that well-dispersed ribbon-like nanofillers (GNR) formed a network structure activated by formation of primary and secondary entanglements between adsorbed polymer chains and bulk polymer chains. However, tube-like nanofiller (MWCNT) presented a strongly flocculated network structure formed through the direct tube-tube contact and mechanical entanglements. This seemingly inferior characteristic of nanoribbons has been utilized as an advantage to develop hybridized nanocomposite systems for charge storage applications.
Description
Keywords
Chemistry--Polymer
Citation
Sadeghi, S. (2016). Use of Rheology to Assess Structures in Polymer Nanocomposites (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/28611