Executive Summary : | Dilute colloidal gels are stringy particulate networks formed by quenching dilute suspensions of colloidal particles through strong attractive interactions. Their sample spanning fractal microstructure and arrested microdynamics leads to a soft, solid like elastic rheology. This elastic property of dilute gels is commonly used to impart quiescent stability in several industrial and commercial complex fluids. Yet, rheological control in gels produced from spherical colloids is surprisingly limited due to the universal characteristics of their fractal cluster microstructure. Consequently, the scope for manipulating their linear elastic modulus is largely restricted to a single universal curve on the modulus-volume fraction space. This limitation presents a compelling need to develop scientific principles for extending the scope for elasticity control in this important class of soft matter in ways that are not bound by universality constraints. The latter forms the scientific objective of this study. Recent discoveries show that gels produced from shape anisotropic discoids exhibit non-universal characteristics, such as aspect ratio dependent fractal dimension and rheological functions that are shifted from the universal curve seen for spheres. We here argue that non-spherical colloids therefore hold great potential to expand the otherwise narrow design space of dilute gel rheology. However, fundamentally, the underpinnings of how particle shape anisotropy drives these unusual behaviours remain unknown. This gap impedes the applicability of anisotropic colloids for gel design. In pursuit of the above objective, this proposal seeks to address this fundamental gap by asking: (1) why and how anisotropy of particle shape introduces non-universality in the gel microstructure, (2) how such structural changes impact the gel microdynamics and, (3) how changes to structure and dynamics combine in the context of microrheological theories to generate aspect ratio driven shifts in gel rheology. These questions will be addressed through experiments involving anisotropic colloid synthesis, self-assembly, confocal and time lapse microscopy, morphological and particle tracking image analysis, dynamic light scattering and, rheometry. The study’s outcome would be twofold; it will (1) establish new fundamental knowledge on the mechanics of anisometric fractal gels, of which currently very limited insights are present, (2) expand the scope for controlling gel elasticity beyond the universal curve of sphere gels by establishing new quantitative correlations between gel modulus, aspect ratio, and volume fraction. Moreover, the study’s impact is that the outcomes will be rooted in fundamental soft matter physics and rheology, thus making them applicable across a range of soft matter gels, enabling formulation scientists to rapidly realize gels of target elasticity. Ultimately, this would lead to low material consumption and improve manufacturing sustainability. |