Edge fracture of thixotropic elastoviscoplastic liquid bridges

Abstract

It has recently been shown that torsion can break liquid bridges of viscoelastic fluids, with potential application to their clean and rapid dispensing [Proc. Natl. Acad. Sci. U.S.A. 118, 24 (2021)]. However, many commonplace fluids (paints, adhesives, pastes, and foodstuffs like chocolate) have more complex thixotropic elastoviscoplastic (TEVP) properties that depend on the imposed stress and the timescale of deformation. Using a commercial thermal paste, we show that liquid bridges of TEVP fluids can also be broken by torsion, demonstrating the applicability of the technique for improved dispensing of real industrial fluids. The liquid bridge breaking mechanism is an elastic instability known as “edge fracture’. Dimensional analysis predicts that the effects of thixotropy and plasticity can be neglected during edge fracture. Simulation using a nonlinear, phenomenological TEVP constitutive model confirms such a prediction. Our work yields new insight into the free-surface flows of TEVP fluids, which may be important to processes such as electronic packaging, additive manufacturing, and food engineering.

From yield stress to elastic instabilities: Tuning the extensional behavior of elastoviscoplastic fluids

“…This characteristic plays a crucial role in diverse phenomena, such as the loss of fore–aft symmetry and the formation of negative wakes behind sedimenting particles ( 9 , 10 ), and the inverted teardrop shape of bubbles rising through EVP fluids ( 11 , 12 ). In practical applications, such as 3D printing, the extensional behavior of EVP fluids can enhance process efficiency ( 13–15 ), yet it is often accompanied by challenges like the formation of secondary droplets and elongated capillary tails that compromise precision ( 16 ). Traditional model EVP gels used in lab settings, such as Carbopol and Laponite, possess limited extensibility, which contrasts with the demands of application-specific materials like printing resins.…”