FYFD

Tag: capsules

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    Viscoplastic Drop Impact

    There are many materials that don’t behave exactly as a fluid or a solid, instead displaying characteristics of both. In this video, we see drops of hair gel falling into water. The gel is viscoplastic – showing some of the viscous behavior of a fluid and some of the plastic behavior (the inability to change back to its initial shape) of a solid.

    On impact, the gel deforms due to the forces on it, but the final shape does not depend solely on the amount of force; instead, it’s the rate at which the forces are applied that determines the final shape. By tuning the impact speed and the gel stiffness, it’s possible to make many final capsule shapes, something that could be useful in applications like drug manufacturing. (Image and video credit: M. Jalaal et al.)

  • Capsule Impact and Bursting

    Capsule Impact and Bursting

    Nature and industry are full of elastic membranes filled with a fluid, from red blood cells to water balloons. A new study looks at how these capsules deform — and sometimes burst — on impact. The researchers created custom elastic shells that they filled with various fluids like water, glycerol, and honey, then used the impacts to build a model of capsule deformation.

    They found that there’s significant overlap between droplet impacts and capsule impacts, with a few key differences; instead of surface tension, capsules resist deformation through their elastic shell’s surface modulus — a combination of its elasticity and thickness. Capsules, unlike droplets, can also burst. To study this, the researchers used water balloons, which they were able to pre-stretch more easily than their custom shells. They found that their model could accurately predict the conditions under which the balloons burst.

    The authors hope the model will be helpful both in designing capsules intended to burst — like a fire-fighting projectile — and in creating safety measures to prevent capsule burst — like car-crash standards that protect from organ damage. (Image and research credit: E. Jambon-Puillet et al.; via Physics World; submitted by Kam-Yung Soh)