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Scientists created a gel, which can turn hard with a touch of a salt crystal

Posted August 4, 2019

There are four fundamental states of matter: solid, liquid, gas, and plasma. Of course, there are many more intermediate states (such as neutron-degenerate matter or liquid crystals), but these four are the most common in everyday life. In order for some material to change from one state to another, usually temperature is required. Except for this new synthetic material, developed at the University of Waterloo.

Sal-gel can turn hard with a touch of a salt crystal, but can return to a normal gel state with some heat. Image credit: University of Waterloo.

It would be cool to have materials that would change their property according to the environment they are in. They could get hard or soft when needed without the need of drastic temperature changes. And this is what the so-called sal-gel is. Sal-gel gets its name from it being a gel, which contains salt. It’s been developed by combining supercooled melted salt with polymers to produce a transparent, stable gel. Its impressive properties could one day be very useful in adhesives, electronics, robotics and even aeronautics.

To be honest, sal-gel does look like a magic material. It freezes (turns into a hard solid) after being touched with a crystal of the salt. It becomes  a hard, opaque solid, but it is not really frozen – it stays at room temperature. And this process is reversible – by applying just a little bit of heat you can turn sal-gel back into its gel form. But how does it work?

Well, the process is called supercooling – this is the basic principle behind this material. Scientists have to use supercooled melted salt, which essentially means that its temperature is below its normal freezing point. Supercooled liquids are still liquids, but they can solidify with the slightest of disturbances. In this case, a salt crystal is introduced and it becomes a starting point for the delayed freezing of the supercooled melted salt.

This could be useful in soft robotics – robot’s arms could be flexible when it needs grip, but stiff when it needs strength and rigidity. Aleksander Cholewinski, co-leader of the research, said: “It should be particularly effective for applications that require a gentle touch, but a firm grip. It is a two-in-one solid that meets both of those needs”.

Of course, as usual, more research needs to be done in order to fully understand how this works and how it could be applied in engineering and science. So far scientists have only experimented with smaller samples. In next stages they could move onto bigger, more demanding objects. It is important to find, how sal-gel would react in different environments. But so far, so good – scientists do believe that it has potential.


Source:  University of Waterloo.

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