Erratum: "Review on the dynamics of isothermal liquid bridges" [ASME Appl. Mech. Rev., 2020, 72(1): 010803; DOI: 10.1115/1.4044467]

We correct the equations for the surface stresses associated with the shear and dilatational surface viscosities

Torsional fracture of viscoelastic liquid bridges

Short liquid bridges are stable under the action of surface tension. In applications like electronic packaging, food engineering, and additive manufacturing, this poses challenges to the clean and fast dispensing of viscoelastic fluids. Here, we investigate how viscoelastic liquid bridges can be destabilized by torsion. By combining high-speed imaging and numerical simulation, we show that concave surfaces of liquid bridges can localize shear, in turn localizing normal stresses and making the surface more concave. Such positive feedback creates an indent, which propagates toward the center and leads to breakup of the liquid bridge. The indent formation mechanism closely resembles edge fracture, an often undesired viscoelastic flow instability characterized by the sudden indentation of the fluid’s free surface when the fluid is subjected to shear. By applying torsion, even short, capillary stable liquid bridges can be broken in the order of 1 s. This may lead to the development of dispensing protocols that reduce substrate contamination by the satellite droplets and long capillary tails formed by capillary retraction, which is the current mainstream industrial method for destabilizing viscoelastic liquid bridges.

A Pore Scale Characterisation of Plant Mucilage - Integrating Imaging, NMR, and Polymer Modelling

<p>Plant roots secrete polymeric gels during root growth known as mucilage, which aid in root growth, nutrient acquisition, and water retention. Mucilage plays an important role in augmenting many soil physical and biogeochemical processes local to the root zone. However, most studies infer the effects of mucilage by reporting changes in the bulk soil. This investigation quantifies the isolated physical behaviour of plant mucilage in a highly simplified soil-analogous environment. We placed drops of hydrated mucilage between two flat surfaces to form liquid bridges and monitored their evolution under drying conditions considering different mucilage mass fractions. We used this information to develop a multi-phase model that characterises the mucilage-water interactions based on a polymeric description of the mucilage volume fraction. Unlike pure water liquid bridges that rupture, the hydrated mucilage liquid bridges collapsed under drying, but maintain connection between the surfaces. NMR imaging shows loss of water from the liquid bridge, particularly from the regions furthest from the surface contacts. Model of drying liquid bridges quantifies mucilage accumulation near the corners of the boundary where the adherence to surfaces is likely to occur. The modelled accumulation times overlapped with monitored bridge collapse for the different mass fractions. Consistency with the model and measurement results highlight the model’s ability to predict a transition when the hydrated mucilage mixture no longer behaves like a liquid. Results suggest that diffusion type models are not adequate for describing pore scale mucilage transport processes, indicating that mucilage’s zone of influence is local to the root, and the transition out of this zone is spatially sharp.</p>