Rheological characterization and modeling of micro- and nano-scale particle suspensions

In recent years there has been increased interest in the broad areas of micro- and nano-technology due to the potential to create materials with unique properties which were previously unattainable. One area of special interest has been the use of nanoparticles such as nanoclays, nanofibers and carbon nanotubes and microscale carbonyl iron particles. Nanoclays and nanofibers have received attention due to their ability to be incorporated into polymer matrices and impart functionality such as electrical conductivity, increased tensile strength and modulus, and a reduction of gas and moisture permeability at much lower particle loadings when compared to traditional fillers such as carbon black and glass fibers. The addition of these nanoparticles also has a significant effect on the rheological properties of the composite. The rheological behavior of polystyrene/nanoclay composites under steady state shear flow and polystyrene/carbon nanofiber composites under transient shear and uniaxial extension is investigated. A constitutive model is developed that is capable of predicting the shear and extensional rheology of both types of composites and predicts orientation changes to the nanoparticles due to flow. The model is validated through comparison to the experimental rheological measurements of both composite types and experimental measurements of carbon nanofiber orientation in the polystyrene/carbon nanofiber composites under uniaxial extension.;The addition of magnetizable carbonyl iron particles to a non-magnetizable carrier fluid has been done to create a smart fluid, known as a magnetorheological fluid, whose rheological properties can be modified through the application of a magnetic field. This added functionality is being utilized in applications such as shock absorbers, dampers, brakes, and clutches. The use of these fluids in engineering applications requires rheological models capable of capturing their complex flow behavior under various flow conditions. The rheological behavior of four magnetorheological fluids were characterized under steady state shear and small amplitude oscillatory shear flow in order to quantify the effects of carrier fluid viscosity and particle size. A constitutive model is developed to predict the shear flow response of the MR fluids which accounts for hydrodynamic forces and the magnetic effects on the carbonyl iron particles. The model is validated through comparison with the experimentally measured data.;Carbon nanotubes have tremendous potential to be used in a wide range of applications because their tensile strength, electrical conductivity and thermal conductivity are among the greatest of all known materials. The performance properties currently achieved in macroscopic assemblies of CNTs are significantly less than those of individual nanotubes and are highly dependant upon processing conditions. There is a need to understand the principals controlling the behavior of carbon nanotube assemblies in order to realize the full potential of these materials and create marketable products. Several different properties of CNTs and CNT structures were measured in an attempt to identify the significant differences which result in the observed behaviors.