Executive Summary : | Colloidal suspension or colloids exists in different forms in nature and they have diverse applications in different fields. Controlling the long-term stability and flow behavior of colloidal suspension is crucial in industrial process. The addition of a third component to control the flow behavior of colloidal suspension has gained lot of interest in recent times due to its versatility. The addition of small amounts of a secondary immiscible fluid to a stable suspension can lead to particle-spanning network formation through the attractive capillary force, known as “capillary suspensions”. The network formation due to the liquid meniscus between the particle modifies the flow behavior from free-flowing suspension to gel-like state which leads to an increase of several orders of magnitude in the viscosity and yield stress compared with binary suspensions. Capillary suspensions' stability and strength can be tuned by changing system parameters such as particle shape, size, concentration, wettability, and volume fraction of the fluids. There has been remarkable progress in understanding the rheological behavior of capillary suspensions of spheres both experimentally and theoretically. The mechanical strength of the capillary suspension depends on the capillary bridge shape and its volume, which is determined by the particle shape. However, the effect of particle shape on capillary suspension behavior is still not understood properly. A systematic study of particle shape effects on capillary suspension behavior will be the focus of the current project. In the proposed project, different monodispersed anisotropic particles (cube, dumbbells, and ellipsoids) will be employed to study the capillary suspension strength and stability. The material and structural properties for different shape particles will be measured by using complementary techniques such as rheological and microscopy studies and their properties will be compared as a function of particle concentration, wettability, and secondary fluid volume. Material properties such as yield stress and shear modulus will be measured to understand the capillary suspension strength for different shape particles. Fluorescent microscopy studies will also be used to understand the effect of particle shape on the nature of the capillary bridges and particle-spanning network structures they form. The direct visualization of capillary bridge breaking under different shear rates will be observed by using a rheo-microscopy setup. The combination of rheological and microscopy studies will elucidate the underlying mechanism of capillary suspension strength to the particle network. From these studies, we will try to find the relation between the yield stress, bridge meniscus, three-phase contact angle, and bridge volume by including the shape correction factors in the existing models. |