Flow blurring atomization of Poly(ethylene oxide) solutions below the coil overlap concentration

Abstract

Atomization of polymer solutions has important technological implications across many fields. Here, we investigated the atomization dynamics of diluted, polymer solutions using Flow Blurring (FB) technology. Aqueous solutions of poly(ethylene oxide) [PEO] of viscosity-averaged molecular weight in the range 100000 g/mol – 4000000 g/mol and varying concentrations were sprayed with a FB atomizer having an orifice diameter (D) of 700μm and a liquid feed-tube-to-orifice separation (H) of 100μm. The solutions belong to the dilute regime, where polymer coil overlap does not occur, that is φ=cmMvMe<φcrit (Modesto-López, Pérez-Arjona, & Gañán-Calvo, 2019). Shear viscosity measurements indicated that the solutions had viscosities of the order of that of the solvent and exhibited a Newtonian-like behavior. However, during the atomization, and due to the relatively high shear stress induced in the atomizer, the solutions exhibit extensional rheology, which most likely arises from the stretching of the polymer chains in-flight. Although initially the atomization resulted in formation of filaments, these broke up into droplets at relatively short distances from the atomizer discharge orifice as elucidated by images from ultra-high speed videos. The phenomenon is in contrast with that observed in FB-based atomization of semi-diluted polymer solutions with concentrations larger than the polymer coil overlap concentration, c∗. FB atomization of the diluted solutions resulted in a decrease in droplet size with increasing the gas-to-liquid mass ratio (GLR). The approach herein aims at understanding the droplet formation dynamics of viscoelastic, polymer solutions with FB, for applications in large-scale synthesis of materials.