Why does ink flow towards the nib of a disposable pen, but does not flow out of the open end of the plastic tube when it is left horizontal?

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Why does ink flow towards the nib of a disposable pen, but does not flow out of the open end of the plastic tube when it is left horizontal?

In: Engineering

The thickness of the ink on thinness of the tube the ink is in create pressure that stops this

It’s a combination of a vacuum and surface tension. If the ink were to flow out the end of the tube, there will need for there to fill the gap with air or something else. The surface tension of the ink helps prevent air from making it’s way down the tube which helps maintain the lack of air at the nib end. Depending on the viscosity of the ink, some companies cap the ink with another substance to ensure that the ink doesn’t flow out.

As for how I figured this out, I stuck a needle down the tube of a disposable pen in the past and some of the ink flowed out.

There is actually a clear liquid/gel at the end that stops the ink from going out the back end. Not sure what it is made of, I assume some kind of silicone.