# Thread: Film in a narrow slit

1. If a thin sheet of some material in which a slit is cut is immersed in a liquid and removed, a liquid film (bridge) stays in the slit. Is it possible to calculate the shape of the film if the properties of the liquid and the dimensions of the slit are known?

2. Hi MlinarM, welcome to the forum. I would think it ought to be possible. What did you have in mind?

3. I think it should still have a concave shape, but how to find the curvature? Several articles that I've read seem to suggest that the shape is determined by the Young-Laplace equation,
Δp = γ(1/r1 + 1/r2)
but how to find the radius of curvature?

4. So the difference in pressure = surface tension x 2 curvature. Do r1 and r2 relate to the two surfaces? Why would they be different?

5. They relate to the same surface: one to horizontal curvature and the other to the vertical curvature. It's a general equation for calculating the pressure difference at a fluid-fluid interface, but I guess in this case horizontal curvature is not significant, so we could write it as Δp = γ/r (if there is no curvature, r2 is infinite, and as r2 goes to infinity, 1/r2 goes to zero). To find the radius from this equation I would need to know Δp... I think Δp must then depend on slit width and adhesion of the liquid to the material, since the curvature must depend on these, but I don't know how?

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