Capillary force when immersed in liquid

[sir_manning]

Hi

I have a question about the capillary force between two hydrophilic surfaces. I am working with small cantilevers (5-50 um long, 5 um wide, 200 nm thick). If L represents the lever, which is hydrophilic, and X represents some bulk material (also hydrophilic), a profile of the lever looks like:

LLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLL
XX
XX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX


The levers are immersed in water and then dried slowly. My question is, when does the lever (L) begin to experience an attraction to the material (X)? Will the capillary force start when it is immersed, or only when there is a small amount of water between the lever and the material? Basically, I'm wondering if I can get around any capillary forces by keeping the cantilevers in water.

Thanks.

 

[Andy Resnick]

I think you are confused about applying the capillary force (which occurs due to the presence of a three-phase line) and interfacial energy (which is the interface between two phases.

Immersing the entire thing in water means there is no three-phase line. Assuming we can ignore differences in the polarizibility between air and water (which could affect the interaction energy between 'L' and 'X'

The presence of a three-phase line means there is a force acting on the substrate- this is not an attraction to 'X', but a consequence of the different energy between a water/'L' interface and an air/'L' interface.

Or am I not understanding your question?

 

[sir_manning]

So, a 3-phase line is needed for the capillary force to work, since (as you said) the force is a result of the different energy between the L/air and L/water interface.

If there are just two phases, there is still an interface energy, but since there is just one interface, there is no energy difference and therefore no force.

Is this a correct summary of the situation? Thanks for the reply.

 

[Andy Resnick]

Don't forget the water/air interface at a three phase line, but basically, that is correct.

 

[pmacias]

Hello, thank you for your question. The capillary force between two hydrophilic surfaces is caused by the surface tension of the liquid (in this case, water) and the adhesive forces between the liquid and the surfaces. When the lever (L) is immersed in water, the liquid will wet the surface and form a meniscus at the edges of the lever. This meniscus creates a curved surface, with a concave shape towards the lever, and results in a downward force on the lever. This force is known as the capillary force.

The strength of the capillary force depends on several factors such as the surface tension of the liquid, the contact angle between the liquid and the surfaces, and the distance between the surfaces. In your case, the capillary force will start when the lever is immersed in water, as the liquid will immediately wet the surface and form a meniscus. As the lever is slowly dried, the amount of water between the lever and the material (X) will decrease, but the capillary force will still be present.

Keeping the cantilevers in water may help reduce the capillary force, but it may not completely eliminate it. The strength of the capillary force will decrease as the water evaporates, but it may still be present to some extent. Additionally, keeping the cantilevers in water for an extended period of time may lead to other issues such as corrosion or growth of microorganisms. It is important to consider these factors when designing your experiment.

I hope this helps answer your question. If you have any further inquiries, I would be happy to assist. Best of luck with your research.