Heterogeneous materials encompassing a diverse range of materials and structures are fundamental and ubiquitous in nature, industries and material engineering. Such systems include polymer composites, emulsions, lava, particle suspensions, active colloids, biopolymer networks, microgels, soil etc. These systems generally comprise distinct phases and components such as macromolecules, particles, networks and force chains which are of multiple length scales, each with unique rheological properties. Understanding such material systems requires proper inspection of structural complexities, material interactions and dynamics of flow. Given the multiple microstructural mechanisms, the question of interest is: can rheology of these systems be studied using different tools, such as non-linear deformation and thin gap rheology? With that motive, few model and realistic heterogeneous systems with varying heterogeneity i.e. chemical, structural and size are investigated in this study. Systems of our interest are gels, mucilages, particle suspensions and their mixtures.
Given the complexity and ubiquity in nature, it would be interesting to study model heterogeneous systems which are close to much more complex real ones. Non-linear rheology has already been used to characterize various biopolymers such as pectin, agarose and alginate. However, a real heterogeneous system like seed mucilage has not been investigated from a fundamental point of view. Hence, this work highlights the large amplitude deformation behaviour of seed mucilage and aims to unravel the contributions from its inherent structural heterogeneity to the response. On a parallel note, numerous systems such as soft microgels, carbopol gels, monodisperse suspensions containing glass spheres, clay suspensions and even biological fluids under confinement conditions are studied both experimentally and computationally. In most of these studies, the primary focus has been on particle dynamics, particularly in relation to yield stress variations with confinement. Yet, knowledge gap persists when it comes to comprehending the response of polydisperse suspensions characterized by high volume fractions of particles and intricate force chain networks. Additionally, the effect of confinement on the elasticity of heterogeneous systems endowed with structural networks has been of research interest. To address this, thin gap rheology of these systems is characterized and presented.