Research Projects

A wide range of physical behaviour are exhibited by colloidal dispersions, systems consisting of fine particles dispersed in a continuous medium. Comprehending the interactions between the constituent particles is essential for tailoring colloidal stability and promoting fabrication of materials in sectors spanning from food processing and pharmaceuticals to coatings and ceramics. The phase behaviour of colloidal dispersions is typically interpreted through the lens of classical interparticle forces: Van der Waals attractions, electrostatic repulsions, steric hindrance, and external fields such as electric, magnetic, etc. Colloid–polymer mixtures have long served as model systems for understanding entropic interactions, particularly depletion forces arising from the presence of non-adsorbing polymers. In most cases, depletion interactions in dispersions of spherical colloids have been extensively investigated, and that on anisotropic colloid (such as rods, platelets and ellipsoids)-polymer mixtures have been sparsely explored. Understanding how anisotropic shape modulates interaction potential, spatial correlations, and structure formation is of fundamental importance in soft matter and biological systems and can significantly impact formulation design in coatings, pharmaceuticals, and nanocomposites. The proposed work aims to explore the thermo-reversible depletion interactions in ellipsoidal colloid-polymer mixtures as a function of aspect ratio. Hematite ellipsoidal particles will be synthesized and the surface chemistry of the particles will be altered by coating them with silica shell. Hematite will then serve as a template to produce hollow silica ellipsoids. Poly(N-isopropylacrylamide) also referred to as pNIPAM, a thermo-responsive polymer will be added as depletants. Our interest is to explore the effect of thermo-reversible depletion interactions on hematite ellipsoid particles, silica coated hematite particles and hollow silica ellipsoid particles with different aspect ratios by the addition of pNIPAM microgel particles. The temperature of the dispersion medium will be varied across the volume phase transition temperature (VPTT) of PNIPAM to induce and control depletion interactions. We envision that the temperature dependence of pNIPAM microgel size may play an important role in tuning depletion interactions, thereby, packing and gelation or aggregation in these systems, which will be quantified by rheology, microscopy and small angle x-ray scattering (SAXS) experiments. Increasing the temperature and subsequently cooling it back is expected to induce reversible gelation in the system, as VPTT of pNIPAM is reversible, and hence this system is ideal for experimental study. The goal is to understand how colloidal particle shape, aspect ratio and temperature of the medium affects the depletion layer thickness, range and strength of interaction, and collective behaviour such as clustering, gelation, or phase separation.