Rheology Of Particulate Dispersions And Composites PDF Download

Particle dispersions are ubiquitous in our daily lives ranging from food and pharmaceutical products to inks. There has been great interest in the recent years in formulation of functional inks to fabricate myriad flexible electronic devices through high-throughput roll-to-roll technologies. The formulations often contain several functional additives or rheological modifiers that can affect the microstructure, rheology and processing. Understanding the rheology of formulations is important for tuning the formulation for optimal processing. This thesis presents investigations on the rheology of particle dispersions and their impact on roll-to-roll technologies. Shear-thickening behavior is common in particle dispersions, particularly, concentrated particulate inks. We have investigated the elongational rheology of a shear-thickening particle dispersions. We find that, an optimal polymer concentration resulted in a strong strain-hardening behavior with a magnitude that is significantly larger than the shear-thickening magnitude. Understanding the non-linear viscoelastic behavior of materials is very important, as deformations in applications are typically large. The rheology of three shear thickening dispersions with different thickening mechanisms was studied. Strong differences in the viscoelastic non-linearities in the three shear-thickening dispersions were observed. We next study the impact of rheology of shear thickening particle dispersions in gravure printing and slot die coating processes. In gravure printing, an efficient transfer of ink from gravure cell to the substrate is desired to print patterns with good print quality for desired product performance. We have conducted a study on how a shear thickening rheology impacts the amount of ink transfer. Distinct ink transfer behaviors associated with an extensional thickening, and an extensional thinning of the test fluids were observed. In a slot-die coating process, obtaining highly thin uniform defect free films at high speeds is a challenge. We have investigated the role of shear-thickening rheology on the stability of coating and the process window. The onset of shear-thickening was found to reduce the maximum web speeds for stable coating through the evolution of a ribbing defect. The presented investigations on the rheology of particle dispersions and their influence on roll-to-roll processing behavior would enable tuning of ink formulations and optimizing the process parameters towards fabrication of flexible electronics.