Time dependence of nonlinear flow dynamics of near hard sphere suspensions

Nonlinear rheology;Rheology and small-angle neutron scattering (Rheo-SANS);Hard spheres

Kumar, Mansi Agarwal

关键词: Nonlinear rheology;    Rheology and small-angle neutron scattering (Rheo-SANS);    Hard spheres;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/98110/KUMAR-DISSERTATION-2017.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The mechanical properties of near hard sphere suspensions are studied from low frequency to high frequency terminal regions as a function of frequency and strain. The volume fraction dependence of experimentally observable characteristic time scales are reported- the longest relaxation time and two cross over times: the first denoting the end of the low frequency terminal region where the linear storage modulus first exceeds the loss modulus and the high frequency cross over time where loss modulus exceeds the storage modulus. At low frequencies where the viscous behavior dominates, the onset of nonlinearities is driven by increases in rate of strain. At higher deformation frequency, where suspension mechanics is dominated by an elastic response, the nonlinear responses occur when deformation exceeds a characteristic strain. This strain is associated with the transient confinement of particles by nearest neighbors and its volume fraction dependence is through cage parameters derived from the high frequency elastic modulus. The onset of nonlinear responses takes on a universal behavior when deformation frequency is normalized by the characteristic time governing the shift from viscous to elastic behavior at low frequency indicating that this transition is associated with transient particle localization and is expected to be observed for all volume fractions where pair interactions are important. Small angle neutron scattering experiments were used to characterize the suspension microstructure under steady shear and in the low frequency terminal region and the resulting scattering was expanded using spherical harmonics. The coefficients of the spherical harmonics are successfully used to predict the stress response of the microstructure under steady shear, and, for the first time, for near hard sphere suspensions, under oscillatory shear.