(390g) Rheology and Structural Investigation of Fumed Silica Based Shear Thickening Fluids

Rheology and Structural Investigation of Fumed Silica Based

Shear Thickening Fluids

Justin Warren², Santanu Kundu^1*, Kathleen Weigandt³, Thomas Lacy², Hossein Toghiani¹, Charles U. Pittman, Jr.⁴,

1. Dave C. Swalm School of Chemical Engineering, Mississippi State University, MS State, M , 39762
2. Aerospace Engineering, Mississippi State University, Mississippi State University, MS State, MS, 39762
3. National Institute for Standards and Technology, Gaithersburg, MD, 20899
4. Department of Chemistry, Mississippi State University, MS State, MS, 39762

 * Corresponding Author: santanukundu@che.msstate.edu

Shear thickening fluids (STFs) are increasingly being investigated in various applications ranging from improving the ballistic impact resistance of body armor to damping the vibration of alpine skies to shielding spacecraft structures from micrometeoroid/ orbital debris (MMOD) impact.  Spacecraft MMOD shields can be subjected to wide temperature variation, often more than ±100 ^oC.  Therefore, an understanding of shear-thickening responses as a function of temperature is critical.  Here we report the results of rheological characterizations as well as small angle and ultra small angle neutron scattering (SANS and USANS) experiments performed on fumed silica nanoparticle based STFs where both the temperature and shear rate were varied.  In addition to varying the mass fractions of the dispersed phase, the interactions between the dispersed and continuous phases were controlled by altering the surface chemistry of the suspended fumed silica particles and the molecular architecture and molecular weight of the suspending media.  STFs were prepared by suspending fumed silica nanoparticles (~120 nm in characteristic length) with different surface functionalities in polyethylene glycol (molecular weight of 200 g/mol and 400 g/mol) and polypropylene glycol (molecular weight 700 g/mol).  Rheological characterizations were performed in a shear-rheometer over a temperature range of -60 °C (melting point of the continuous phase) to +50 °C, and SANS and USANS rheological experiments were carried out over a temperature range of -40 °C to +40 °C.  The STFs’ viscosity was greatly dependent on temperature and shear rate, and the SANS and USANS results were used to characterize the structure as a function of temperature and shear rate.