If you are looking for a sealing material that can penetrate small and narrow gaps, it is not always obvious that a liquid material with very low viscosity is the best choice.
The picture shows a drop of water and a drop of silicone oil. Both drops have exactly the same mass. The water sticks together, but the silicone oil quickly flows out and forms a very thin 'lens'. Water has a viscosity of 1.0 mPas while the silicone oil in the picture has a viscosity of 4000 mPas. You could say that the silicone oil flows 4000 times slower, and that is a big difference. Nevertheless, the silicone oil covers the surface much better by far. This effect is due to surface tension, i.e. the forces that tend to hold the surface of the material together.
This effect is of some importance when choosing the appropriate adhesive or sealant. If you want a sealant to fill small gaps, a water-based sealant would not perform well. The high surface tension of water means that it tends to form droplets in the surface layer and will not flow into the smallest cavities. This effect is particularly evident when water is applied to plastic surfaces. In contrast, a silicone-based sealant would work much better.
Now, water has unusually high surface tension and silicone has very low surface tension. But it is also the case that silicone has significantly lower surface tension than many other types of polymers, including most thermoplastics. This allows silicone varnishes, adhesives and sealants to 'flow out' over most surfaces, increasing the possibility of creating strong intermolecular bonds. This is one of the reasons why silicone adhesives can bond plastics that are otherwise difficult to bond, without first having to raise the surface tension of the substrate.
Do you have a still unsolved glue problem? Feel free to contact us at Tribotec. Maybe we have a material that works without any primer or cumbersome pre-treatment.
