Like every Friday, the weekly "Physics Bite" column is back — number 23.
This time: the Rehbinder effect and surfactants.
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The Rehbinder effect is named after the Soviet chemist who discovered it in 1928.
It describes the influence of surfactants on the hardness of solid materials.
The video shows a demonstration of the effect — when the glass is submerged in water, it can be pierced without shattering.
The effect has numerous applications in the metals industry and in lubricants.
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How does it work?
The reason that driving a nail through a glass causes it to shatter is that its surface is hard.
The material's molecules are bonded to one another, so the energy of the impact travels through them and creates microcracks that propagate through the material until it shatters.
When the glass is submerged in water, the water weakens the attractive forces between the material's molecules, making it more flexible and preventing the impact energy from propagating further.
The reason water weakens the intermolecular attraction is that it acts as a buffer between the molecules.
One side of each water molecule is attracted to the material's surface, while the other side faces outward toward neighboring water molecules.
Materials that behave this way are called "surfactants" — familiar to us in the kitchen in the form of dish soap and degreasers.
Shabbat Shalom 🌹
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