Friday is here again, and with it the weekly "A Taste of Physics" column — number 24.
This week: polymers, osmosis, and a wonder powder that absorbs water.
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The powder in the video is called sodium polyacrylate.
It can absorb a staggering amount of water — up to 800 times its own volume.
The powder has many everyday uses and can be found, for example, in baby diapers and bandages.
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How does it work?
The powder is essentially a polymer — a giant chain of molecules produced artificially in a laboratory.
The polymer chains are cross-linked in an ordered structure, which is why the powder occupies such a small volume.
The polymer contains negatively charged ions.
Water molecules are polar molecules — they have a negative pole and a positive pole.
The polymer's negative ions act like a magnet, attracting the positive poles of the water molecules toward them.
As water molecules bind to the polymer chains, the chains separate from one another and form a swollen three-dimensional network, drawing in more and more water.
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If we add salt to the water, the polymer's ability to absorb it decreases significantly.
The reason is that salt contains positively charged ions, which bind to the polymer in a similar way to water and therefore compete with water molecules for the available binding sites.
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The water absorption process also involves another phenomenon — osmosis.
Osmosis occurs when a solvent (such as water) is drawn through a membrane toward the side where the concentration of dissolved particles is higher, thereby diluting it.
This is a somewhat complex topic and we won't go into it in depth today.
In our case, osmosis also plays a role in the absorption of water into the polymer, in addition to the electromagnetic attraction.
Shabbat Shalom 😊
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