Computational Studies on Multi-phasic Multi-componentComplex Fluids

Advancement in computational capacity combined with the emergence of efficient algorithmshas made the computational studies very powerful and desirable. Despite the greatimportance of complex fluids such as emulsions, colloidal suspensions, and gels in manyapplications, some of their physical and mechanical properties remain poorly understood.To understand rheological and mechanical properties of such systems, one needs tounderstand their properties at different time and length scales through careful multiscaleanalysis. To answer these questions, we use Dissipative Particle Dynamics as a versatilecoarse-grained method to gain a better understanding of different scales and bridge the gapbetween the microscopic and macroscopic worlds in particulate multicomponent complexfluids.In Chapter 1, briefly, we introduce the DPD mathematical and physical formalism. InChapter 2, we examine different algorithms to measure the transport properties of a simpleDPD fluid and introduce the new computational method to measure the viscosity of DPD liquids under non-equilibrium conditions to account for the numerical instabilities. InChapter 3, we discuss the properties of multiphasic systems mainly liquids in liquids. Weinvestigate the effect of molecular composition, configuration, and conformability ofsurface active molecules in stabilizing immiscible mixtures for flat interfaces as well ascurved interfaces. The final section of chapter 3 is dedicated to studying the effect of sheardeformation on the geometrical evolution of surfactant covered nanodroplets. In chapter4, we mainly focus on colloidal suspensions and their rheological responses in nonlineardeformation. Through network analysis, we show that the frictional bonds form a percolatednetwork at volume fractions close to jamming while at volume fractions well belowjamming the frictional networks are transient and unstable. Measuring viscosity and normalstresses show the discontinuous transition occurs in the viscosity and positive values forthe first normal stress which is concomitant with the formation of the percolated network.In Chapter 5, we look at mechanistic behavior of colloidal particles with short-rangedattraction potential. We observe a two-step yielding transition under start-up deformationand explained it through careful analysis of the microstructure. It was shown thathydrodynamic interactions are important to explain this behavior at high deformation rates.