Research Projects

Wall slip is a critical phenomenon in the processing and performance of polymer-based materials, which are found in almost every soft product used in daily life, like shampoo, toothpaste, creams, paints, plastic packaging, bottles, films, and automotive parts. During manufacturing processes such as extrusion, injection molding, coating, or pumping, these polymer systems flow through confined spaces like dies, pipes, or nozzles, wherein wall slip becomes a critical factor, especially in the case of high shear rates or highly entangled molecular structures. Near the wall, polymer chains can align, stretch, disentangle, or form low-viscosity layers near surfaces, allowing slip to occur. Understanding wall slip is very crucial because it can help in predicting flow behavior, avoiding defects, improving manufacturing efficiency, and ultimately ensuring product consistency, quality, and performance. Improper control of slip can lead to defects such as melt fracture, uneven coating, or poor adhesion. Deeper understanding of the factors that govern wall slip such as polymer-polymer interactions, surface properties, shear conditions, and molecular structure is vital. An interesting class of such polymer-based system is a dispersion of polymer-grafted nanoparticles (PGNPs) wherein polymer brushes grafted to nanoparticles interact both with each other and with free matrix polymers or other brushes near walls. The wall slip phenomenon in PGNP dispersions can arise from several interfacial mechanisms, including interactions between grafted polymer brushes and the wall, entanglements between the grafted chains and free polymers or neighbouring brushes, formation of lubrication layers, and particle layering near surfaces. These interfacial mechanisms are influenced by factors such as grafting density, polymer chain length, nanoparticle concentration, and shear rate. Understanding wall slip in PGNP dispersions is essential not only for accurate rheological characterization but also for the optimization of various processing techniques, for example, in microfluidics and inkjet printing, wherein wall slip reduces flow resistance and improves print precision by enabling smooth, controlled movement through narrow channels or nozzles. In extrusion and 3D printing, slip facilitates easier processing by lowering shear stress and preventing defects like die swell or surface irregularities. Slip also enhances lubrication by forming low-friction interfacial layers. In film coating and deposition, controlled slip helps achieve uniform, defect-free layers. Despite its significance, the wall slip phenomenon in PGNP-based materials remains insufficiently understood. So far, no work has been reported in the literature addressing the wall slip in PGNP dispersions. Therefore, a systematic investigation of slip mechanisms in PGNP dispersions is essential for both improving theoretical understanding and optimizing real-world processing and application of these advanced materials.