Abstract:
Shear thickening (ST) is a well-known phenomenon observed in suspensions, characterized by an increase in viscosity with applied shear stress. Recent advancement in
our understanding indicates the role of inter-particle surface contact friction in ST of
dense suspensions. In such suspensions with an increase in volume fraction of particles,
ST also increases and transits from continuous shear thickening (CST) to discontinuous shear thickening(DST). In the DST regime, the presence of a negative slope in
shear-stress versus shear-rate plot indicates the presence of flow instability. No such
instability is expected or observed in the CST regime. In this thesis, we study whether
surface friction of the particles plays any role in ST, and are flow instabilities present
in suspensions of anisotropic particles in the CST regime.
This thesis consists of four chapters. Chapter 1 provides a brief introduction to two
different models which try to explain ST in suspensions. The first model is the hydrodynamic model and the second one is the inter-particle frictional model. In the latter
part of this chapter, various strategies for tuning ST are discussed. Chapter 2 provides
details of the experimental setup and synthesis protocols followed to synthesize silica
colloidal rods and coat them with temperature-sensitive polymers. Chapter 3 discusses
the findings from our studies which can be subdivided into two different sections. In the
first section, temperature-sensitive polymer-coated colloidal rods are used to tune the
surface friction and their flow behavior as a function of temperature is studied by suspending them in aqueous medium. In the second section, flow instabilities are explored
in the CST regime in the suspensions of silica colloidal rods and water-glycerol mixture. To do so, stress relaxation measurements are performed at different volume fractions
for two different measuring system geometries. Chapter 4 concludes our findings and
provides insight into our understanding of the subject so far.
