Experimental investigation of surfactant influence on the viscoelastic coaxial electrospray

This study investigates the formation of a core-shell cone jet for encapsulating sunflower oil within a viscoelastic alginate solution via coaxial electrospray, with particular emphasis on the impact of surface tension by surfactant addition. Alginate, a naturally occurring linear polysaccharide, is widely used as an encapsulant due to its low cost, ease of use, and biocompatibility. High-speed imaging was employed to capture various electrohydrodynamic (EHD) modes by adjusting the applied electric potential between the coaxial nozzle and the ground electrode. The influence of operating parameters and surfactant addition on the formation of cone jet profiles was systematically analyzed. The results demonstrate that surfactant addition expanded the stable cone jet region by 132.8 % (2.33 times) on the operating maps, enabling the formation of a stable cone jet even at low Weber numbers. Surfactants enhance the miscibility between the core and shell fluids, and induce a corrugated interface, leading to an increase in the meniscus jet diameter. However, the stability of the jet at lower Weber numbers facilitated the creation of smaller particles. As the Weber number increased, the cone angle initially decreased and then increased, which is attributed to the changing viscoelastic behavior of the alginate solution under varying shear rates. Additionally, the use of surfactants reduced the cone angle of both the outer and inner fluids due to a decrease in surface tension forces.