Numerical study of Saffman–Taylor instability in immiscible nonlinear viscoelastic flows

In this paper, a numerical solution for Saffman–Taylor instability of immiscible nonlinear viscoelastic-Newtonian displacement in a Hele–Shaw cell is presented. Here, a nonlinear viscoelastic fluid pushes a Newtonian fluid and the volume of fluid method is applied to predict the formation of two phases. The Giesekus model is considered as the constitutive equation to describe the nonlinear viscoelastic behavior. The simulation is performed by a parallelized finite volume method (FVM) using second order in both the spatial and the temporal discretization. The effect of rheological properties and surface tension on the immiscible Saffman–Taylor instability are studied in detail. The destabilizing effect of shear-thinning behavior of nonlinear viscoelastic fluid on the instability is studied by changing the mobility factor of Giesekus model. Results indicate that the fluid elasticity and capillary number decrease the intensity of Saffman–Taylor instability.     

A MOF@COF Composite with Enhanced Uptake through Interfacial Pore Generation

Herein, we describe a new class of porous composites comprising metal–organic framework (MOF) crystals confined in single spherical matrices made of packed covalent‐organic framework (COF) nanocrystals. These MOF@COF composites are synthesized through a two‐step method of spray‐drying and subsequent amorphous (imine‐based polymer)‐to‐crystalline (imine‐based COF) transformation. This transformation around the MOF crystals generates micro‐ and mesopores at the MOF/COF interface that provide far superior porosity compared to that of the constituent MOF and COF components added together. We report that water sorption in these new pores occurs within the same pressure window as in the COF pores. Our new MOF@COF composites, with their additional pores at the MOF/COF interface, should have implications for the development of new composites.     

PTMG-Modified MWCNT/PTMG-based polyurethane nanocomposites: Strong interaction and homogeneous dispersion

Soft and flexible chains of poly(tetramethylene glycol) (PTMG) were covalently grafted with multi-walled carbon nanotubes (MWCNT). FE-SEM images showed that the polyether PTMG formed a surrounding shell around the nanotubes with about 5 nm in thickness. The modified nanotubes (MWCNT-PTMG) were then loaded into an in situ prepared polyurethane elastomer (PUE) with different loading contents below 1 wt %. In addition to the modifier of MWCNT, polyether PTMG was also used for preparing the polyurethane matrix. Thermal analyses (TG/DTG and DTA) showed two endothermic phase transitions in associated with the two main thermo-degradations of the resulting PUE nanocomposites. Moreover, DMA technique exhibited an appreciable increase in the T _g values due to a strong interaction between PTMG-modified MWCNT and PTMG-based PUE matrix.