Numerical simulation of complex soft matter systems

Official URL: https://risc01.sabanciuniv.edu/record=b2767415_(Table of contents)

Soft matters are the branch of materials that can be deformed or structurally altered under mechanical stress. These materials have contributed to many engineering applications, including microfluidics, 3D printing, and tissue engineering, among others. Of particular interest, two essential and highly desirable in many applications are being considered, including emulsions and active matters. Emulsions consist of a dispersed fluid suspended in an ambient fluid leading to the multiphase system. The water-oil emulsion is one of the well-known examples of these systems, which can be either a single emulsion (W/O or O/W) or the double emulsion (W/O/W or O/W/O), which are the indispensable parts of the microfluidic systems. Active matters describe systems, such as cellular tissue or bacterial suspensions that actively consume their internal or surrounding energy and convert it into motion leading to the collective chaotic motion known as active turbulence. Using numerical simulations based on two different mesh-free and mesh-based schemes, namely smoothed particle hydrodynamics and finite volume methods, we investigate the hydrodynamics of these complex systems, allowing us to control these systems and gain a better understanding of their behavior. First, an electrohydrodynamics simulation of the emulsion is performed. The confinement effects are investigated by placing a single emulsion in a highly confined domain and applying an external electric field. It is shown that the deformation is highly dependent on the ratios of electrical permittivity, electrical conductivity, and confinement ratio. Effects of combined shear and electric forces on the double emulsion are also studied. It is shown that the deformation and orientation angle of droplets are highly iv dependent on the capillary and electrical capillary numbers, and core to shell radius ratio. It is demonstrated that in some systems, a breakup occurs, which can be circumvented by changing the capillary and electrical capillary numbers as well as the core to shell droplet radius ratio. Next, the active nematic is simulated by using the continuum model for the nematodynamic equation. Flow behavior, nematic ordering, topological defects, vorticity correlation, and spectrum of the kinetic energy are calculated and discussed in detail. Furthermore, the active nematics’ mixing behavior is calculated and described qualitatively. The effects of two important parameters, namely, activity and elastic constant, are investigated. It is shown that the activity intensifies the chaotic nature of the active nematic by increasing the pathline and mixing efficiency while the elastic constant behaves oppositely. Additionally, the Impact of fluid inertia on the collective pattern formation in active nematics is investigated. It is shown that an incremental increase in inertial effects results in gradual melting of nematic order with an increase in topological defect density before a discontinuous transition to a vortex-condensate state. The emergent vortex-condensate state at low enough viscosities coincides with nematic order condensation within the giant vortices and the drop in the density of topological defects. It is further shown that the flow field around topological defects is substantially affected by inertial effects. Moreover, the strong dependence of the kinetic energy spectrum on the inertial effects is demonstrated, which recovers the Kolmogorov scaling within the vortex-condensate phase, but no evidence of universal scaling at higher viscosities is found. Finally, the vibrational motion of a cantilever beam placed in active nematics is investigated. It is indicated that the small-scale vortices are the primary mechanism for the energy transfer between the fluid and beam, thereby imposing the oscillatory motion. It is also shown that the intensification of the activity increases peak frequency, and there is a linear correlation between the peak frequency and activity. The reciprocal relationship between viscosity and peak frequency is demonstrated as well.