Sharif Digital Repository

Mesoscopic hydrodynamic equations are solved employing a VOF based method to investigate the equilibrium shape of nanodroplets positioned over various topographic geometries of the supporting substrate for three-dimensional systems. By taking into account liquid-liquid and liquid-solid interactions a complex distribution for inter-molecular forces over the substrates (the disjoining pressure) is observed. In this research we show that motion of nanodroplets not only caused by contact angle difference in drplets two sides, but also depend on disjoining pressure parameters.Geometries with increasing complexities, from wedges to three dimensional edges and wedges, were explored with the main... 

Hydrodynamic mesoscopic equations are solved using boundary integral method to investigate the coarsening dynamics of two dimensional nanodroplets. The dynamics is probed by locating two drops on homogeneous, chemical heterogeneous and physical heterogeneous substrates respectively. For homogeneous substrate, the effect of different parameters like droplets distance, slip boundary condition, surface contact angle and disjoining pressure type on the dynamics is studied. Results reveal that increasing the contact angles to values larger than a critical value may qualitatively change the coarsening process and the profile of the disjoining pressure can appreciably modify the coarsening rate.... 

A droplet placed on the boundary of two solids with different wettabilities will move to the more wettable part. This is a well-known phenomenon and has been extensively used in a variety of processes and applications ranging from biological systems and ink jet printing to the commercial lab-on-a-chip. Because of its importance, many studies are conducted around this phenomenon. The difference between the equilibrium contact angles of the droplet on the two parts gives rise to an interfacial driving force which moves the droplet. Such a motion is not continuous as the droplet slides to the more wettable area, the driving force diminishes and consequently the droplet stops. A non-stop motion... 

This study investigates three-dimensional modeling of nanodroplets over chemically patterned surfaces. The pattern can be established by changing the contact angle on the surface. The problem is studied numerically by solving the thin film equations.Both the long-range and short-range inter-molecular interactions are considered. The numerical procedure is validated by using the theoretical studies. The effects of parameters such as the size of the droplets, the gradient of the surface, and the slip coefficient on the dynamics and speed of droplets and the shape of them during the motion are inspected.By examining the dynamics of the system it is revealed that the velocity of the droplets... 

One of the critical challenges in droplet based micro- and nanofluidic devices is handling the droplet breakup such that a controllable droplet size is produced. The experimental and numerical investigations at the microscale indicate that the droplet size can be well controlled by T junction geometries. In the present study we use non-equilibrium molecular dynamics (NEMD) simulations to investigate this phenomenon at the nanoscale. In order to generalize the study the Lennard-Jones type potential between the fluids and the walls have been considered and the strength and the effective range of the potential are changed to consider a wide variety of materials. Our results reveal that the...