Juan de Dios Hernández Velázquez

arXiv2022

The Viscosity of Polyelectrolyte Solutions and its Dependence on their Persistence Length, Concentration and Solvent Quality

In this work, a comprehensive study about the influence on shear viscosity of polyelectrolyte concentration, persistence length, salt concentration and solvent quality is reported, using numerical simulations of confined solutions under stationary Poiseuille flow. Various scaling regimes for the viscosity are reproduced, both under good solvent and theta solvent conditions. The key role played by the electrostatic interactions in the viscosity is borne out when the ionic strength is varied. It is argued that these results are helpful for the understanding of viscosity scaling in entangled polyelectrolyte solutions for both rigid and flexible polyelectrolytes in different solvents, which is needed to perform intelligent design of new polyelectrolytes capable of fine tuning the viscosity in complex fluids.

cond-mat.soft↗

arXiv2022

The Effective Interfacial Tensions between Pure Liquids and Rough Solids: A Coarse-Grained Simulation Study

The effective solid liquid interfacial tension (SL IFT) between pure liquids and rough solid surfaces is studied through coarse grained simulations. Using the dissipative particle dynamics method, we design solid liquid interfaces, confining a pure liquid between two explicit solid surfaces with different roughness degrees. The roughness of the solid phase was characterized by Wenzel roughness factor and the effective SL IFT (γ_sl^') is reported as a function of it also. Two solid liquid systems differentiated from each other by their solid liquid repulsion strength are studied to measure the effects caused by the surface roughness on the calculation of γ_sl^'. We found that the roughness produces changes in the structure of the liquid, which is observed in the first layer of liquid near the solid. These changes are responsible for the effective SL IFT increase as surface roughness increases. Although there is a predominance of surface roughness in the calculation of γ_sl^', it is found that the effective SL IFT is directly proportional to the magnitude of the solid liquid repulsion strength. The insights provided by these simulations suggest that the increase of Wenzel roughness factor is a direct consequence of the increase in surface area due to the vertical deviations measured in the topography. This, in turn, produces an increase in the number of effective solid liquid interactions between particles, eventually yielding significant changes in the local values of the normal and tangential components of the pressure tensor.

cond-mat.soft↗