White, Kevin Lee (2013-12). Rheology of Model Nanoparticle Suspensions in Epoxy. Doctoral Dissertation. Thesis uri icon

abstract

  • The rheology and linear viscoelasticity of several model nanoparticle suspensions in epoxy have been systematically investigated. Three detailed studies were carried using ?-zirconium phosphate (ZrP) nanoplatelets as model 2-dimensional nanoparticles. The effect of inter-particle interactions was investigated using three different surface modifiers to exfoliate the nanoplatelets. The role of nanoparticle size was separately investigated by synthesizing the ZrP nanoplatelets with average lateral diameters ranging from 100 - 1000 nm. The rheology of highly concentrated suspensions of ZrP nanoplatelets was also probed, and found to show unique properties due to the selfassembly of the nanoplatelets in discrete layers with regular inter-layer spacing. The rheological properties of each model system are discussed based on the motion of the individual particles, and the nature of interaction on local and higher order length scales. Multi-walled carbon nanotubes (MWCNTs) were used as model 1-dimensional nanoparticles. We present a method to disentangle the MWCNTs to individual particles based on a novel functionalization technique. The rheology of suspensions containing the disentangled MWCNTs reveals that flocculation does not occur over long time scales, and suggests that the treatment does not significantly modify nanoparticle size. The role of interaction between particles with different geometries was investigated using suspensions containing electrostatically tethered ZrP nanoplatelets and MWCNTs. The flow properties of this system are proposed to originate from direct interaction between the particles, and the contributions of the individual phases are found to be preserved on distinct length scales. A mechanism is proposed to account for the unique strengthening behavior observed in solid epoxies containing the hybrid nanoparticles. The findings presented here consider a broad range of nanoparticle shapes and sizes, and provide detailed insights into how particle-level effects contribute to bulk response in the liquid state. A framework to understand the fundamental behavior and interaction of isolated nanoparticles is presented based on the rheological signatures. Approaches to relate liquid-state behavior to solid systems are discussed. Future work on the local relaxation processes is anticipated to greatly improve understanding of the interfacial properties and driving forces for phase transitions for more complex systems. Multi-walled carbon nanotubes (MWCNTs) were used as model 1-dimensional nanoparticles. We present a method to disentangle the MWCNTs to individual particles based on a novel functionalization technique. The rheology of suspensions containing the disentangled MWCNTs reveals that flocculation does not occur over long time scales, and suggests that the treatment does not significantly modify nanoparticle size. The role of interaction between particles with different geometries was investigated using suspensions containing electrostatically tethered ZrP nanoplatelets and MWCNTs. The flow properties of this system are proposed to originate from direct interaction between the particles, and the contributions of the individual phases are found to be preserved on distinct length scales. A mechanism is proposed to account for the unique strengthening behavior observed in solid epoxies containing the hybrid nanoparticles. The findings presented here consider a broad range of nanoparticle shapes and sizes, and provide detailed insights into how particle-level effects contribute to bulk response in the liquid state. A framework to understand the fundamental behavior and interaction of isolated nanoparticles is presented based on the rheological signatures. Approaches to relate liquid-state behavior to solid systems are discussed. Future work on the local relaxation processes is anticipated to greatly improve understanding of the interfacial properties and driving forces for phase transitions for more complex syst

publication date

  • December 2013