Fixed contact line helical interfaces in zero gravity

Abstract

Fluid interfaces supported in microgravity by a helical structure are shown to have a more robust stability than more common structures such as liquid bridges. In particular, helical interfaces can take the form of infinite right circular cylinders over a broad range of configurations. In the case of a single fixed contact line support, the infinite cylinder is stable for all cases in which the pitch to diameter ratio is less than / ͱ 3 ͑more tightly coiled interfaces͒. When there are two or more equally spaced fixed contact line supports, the infinite cylinder is stable for all configurations. Furthermore, in the two support case ͑the double helix͒, stability persists for all volumes from the cylinder to zero volume, when the pitch to diameter ratio is greater than 2.082 ͑more loosely coiled interfaces͒. The equivalent to the axisymmetric Young-Laplace equation is derived for helical interfaces. Interfacial stability is determined from equilibrium branch structure following the application of Maddocks' method by Lowry and Steen ͓Proc. R. Soc. London, Ser. A 449, 411 ͑1995͔͒. Perturbations to finite wavelength disturbances are considered for the case of a single helical support. Overall stability envelopes are presented for single and multiple support cases. Limited experimental results verify the infinite length stability limit for the single helical support case.

Microgravity/microscale double-helical fluid containment

“…It has previously been determined that only the fixed pressure stability limit is relevant for helical interfaces of infinite extent (Lowry & Thiessen 2007). This greatly simplifies the stability analysis, as all stability limits then occur at turning points in pressure jump, which is proportional to the sum of the principal curvatures of the interface.…”

“…It has been noted that the double helix (NZ2) alone has the property of continuous stability from the cylinder down to zero volume (Lowry & Thiessen 2007). Neither single-helical supports (NZ1) nor three or more (NR3) evenly spaced supports have this property (Lowry & Thiessen 2007; and there is no reason to expect unevenly spaced, drainable NR3 supports). The double-helical support therefore has the unique property of being an open, fully drainable microgravity container and conduit, and it is reasonable to expect that this property extends to microscale.…”

“…Helical containers can be infinite in extent, unlike liquid bridges, and they can therefore serve as tubes as well as open containers (Lowry & Thiessen 2007). It has been noted that the double helix (NZ2) alone has the property of continuous stability from the cylinder down to zero volume (Lowry & Thiessen 2007).…”

“…It has recently become apparent that helical supports are potentially versatile containers and tubes in microgravity (Lowry & Thiessen 2007). Helical containers can be infinite in extent, unlike liquid bridges, and they can therefore serve as tubes as well as open containers (Lowry & Thiessen 2007).…”

“…Helical containers can be infinite in extent, unlike liquid bridges, and they can therefore serve as tubes as well as open containers (Lowry & Thiessen 2007). It has been noted that the double helix (NZ2) alone has the property of continuous stability from the cylinder down to zero volume (Lowry & Thiessen 2007). Neither single-helical supports (NZ1) nor three or more (NR3) evenly spaced supports have this property (Lowry & Thiessen 2007; and there is no reason to expect unevenly spaced, drainable NR3 supports).…”