General Question

LostInParadise's avatar

How is it possible for such a small amount of gelatin to gel such a large amount of liquid?

Asked by LostInParadise (28948points) July 24th, 2011

The effect is particularly noticeable with agar. I can gel a quart of fruit juice with about a tablespoonful of agar powder. At two tablespoons per fluid ounce, the water has 64 times the volume of the agar. Agar is not very heavy, so I would guess that the weight ratio is even larger. Wouldn’t that mean that the water has more atoms by about two orders of magnitude? How can so few atoms corral so many?

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3 Answers

woodcutter's avatar

I think its in the expansion that causes the mixture to absorb and grow in volume some. Similar to those flat coolies bandanas you soak in water and they puff up and tie them around your neck or wear around your head. Or pampers. It’s just an idea.

thorninmud's avatar

Think of a gelatine (or agar) gel as a sponge. A cellulose sponge is quite lightweight, but can hold many times its weight in water. The sponge is composed of a network of cellulose fibers that are joined here and there to create a resilient network filled with small spaces. Water is drawn into and held in those small spaces by capillary action, a phenomenon related to the property of surface tension. The water hangs in those spaces even though the network is open and there’s no physical barrier keeping the water in.

In a similar way, the very long molecular chains in both gelatin and agar form strands that disperse across the water solution at elevated temperatures, then polymerize as the solution cools by connecting at periodic junctions. The result is a random network extending all the way through the aqueous medium. The spaces that are created are very small—much smaller than the spaces in a sponge—which further amplifies the capillary effect, so that the water is even more effectively immobilized.

So, as in a sponge, that network is mostly space. It takes very little solid material to form this network. 1 gram of gelatine can gel 100g of water.

LostInParadise's avatar

Thanks! That makes perfect sense.

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