Liquid droplets on solid surfaces behave according to forces that determine whether a textile absorbs or repels moisture. In a three-phase system, where a liquid droplet, surrounding air, and a solid surface all meet, a phenomenon called line tension acts at the point where all three converge. Understanding this force, and modelling it accurately, shapes how performance textiles are developed for real-world conditions. New research has addressed both what is known about this physics and where significant gaps remain.
- Surface tension, the cohesive force between two phases, is a well-established principle; line tension in three-phase systems is a related but far less understood phenomenon.
- Droplets resting on solid surfaces, known as sessile droplets, are central to wetting and drying mechanics in textiles, particularly at very small scales.
- Practical applications affected by this physics range across athletic wear, waterproof outerwear, and protective equipment, each of which depends on how liquid behaves at the textile surface.
- The paper 'Tricky Tension' has been published in Nature Physics and addresses wetting mechanics relevant to textile performance and design.
BEHIND THE PAPER: The paper has surveyed the intersection of physics and textile science as a review article, charting what is currently understood about three-phase droplet systems and where gaps in that understanding persist. Warren Jasper, a professor at NC State's Wilson College of Textiles, has focused his research on building more accurate models for correctly predicting the sign and magnitude for the line tension of a droplet.
- The review maps established knowledge on droplet mechanics, including surface tension, the cohesive force between two phases that allows small insects to walk on water, and line tension, the force that acts at the boundary where all three phases converge.
- Athletic wear performance depends on the interaction of all three phases: the fabric takes in sweat, moves it away from the skin, and the moisture then evaporates into the surrounding air.
- Protective equipment used around toxic materials requires the opposite effect, maintaining the sessile droplet on the surface and ensuring liquid does not wet the surface and be absorbed into the fabric.
THE MODELLING GAP: Without accurate mathematical models of how liquid droplets behave on solid surfaces, the practical development of performance textiles stalls at observation. Observation alone cannot explain why a droplet behaves differently on different surfaces, and without that explanation, advances in textile design, waterproofing, and dyeing processes remain out of reach. Building a better raincoat is where mathematical modelling meets experimentation, and the modelling of line tension is where that work is most needed.
- Wetting is influenced by the structure of individual droplets at very small scales, a level of detail that inaccurate models of line tension cannot capture or explain.
- Correctly predicting the sign and magnitude for the line tension of a droplet is among the author's stated areas of interest, since current models vary in their reliability on different surfaces.
- Practical advances that depend on closing this modelling gap include the development of better raincoats and dyeing processes that use less energy.
- The paper's author has outlined how new tools and techniques can help address the unresolved questions that current models have yet to answer.
- The paper's author has stated optimism that the work can help chart a path forward, noting that the research continues to produce surprises despite appearing straightforward.
WHAT THEY SAID
By providing an overview of what we think we know, and outlining how new tools and techniques can help us address unresolved questions, I'm optimistic this paper can help to chart a path forward for this line of research – which seems simple but continues to surprise us.
— Warren Jasper
Professor, Wilson College of Textiles
NC State University
