Dilatant materials are substances that become thicker and more resistant to flow when you apply stress or force to them. These fluids, often called non-newtonian, show a sudden increase in viscosity when they’re stirred, hit, or pressured, effectively acting like a solid under impact. You can observe this behavior in common mixtures like cornstarch and water, which turn rigid when struck but flow easily when left alone.
The core of this phenomenon lies in the way particles interact within the liquid. When you move the material slowly, the particles have enough time to slide past each other, allowing the mixture to act like a fluid. However, if you apply force quickly, the particles jam together. This creates a temporary structure that resists deformation. If you try to move through it slowly, the material yields; if you try to move through it quickly, it locks up.
Understanding the particle behavior
The one thing that decides whether this process works well is the concentration of solid particles suspended in the liquid. If the mixture is too thin, the particles can’t jam together effectively, and the material will simply splash like water. The most common mistake is adding too much liquid to the powder, which prevents the “solid” state from ever forming.
You should view these materials as a transition between states. They aren’t permanently solid or liquid but respond to the energy you put into them. This is why you can run across a pool of cornstarch and water if you move fast enough, but you’ll sink if you stand still. It’s a physical reaction, not a chemical change, so the material returns to its fluid state once the pressure stops.
How dilatant materials work during mixing
- Pour 2 cups of cornstarch into a large, sturdy mixing bowl.
- Add 1 cup of water slowly while stirring the mixture with your hand or a large spoon.
- Stop adding water once the mixture looks like a thick paste that flows when you tilt the bowl but resists your finger when you poke it quickly.
- Adjust the consistency by adding 1 tablespoon of cornstarch if it feels too runny or 1 tablespoon of water if it feels too dry.
- Store the mixture in a sealed plastic container to prevent the water from evaporating, which keeps the material usable for several days.
Tip: If the mixture starts to dry out, just add a small splash of water and stir it again to restore the properties.
Tip: Avoid putting these mixtures down a sink drain, as the material can harden in pipes and cause a significant clog.
Time requirements for preparation
The time needed to reach the desired state depends on the volume of materials you’re mixing and the speed of your movement.
| Situation | How long | What changes it | What to watch for |
|---|---|---|---|
| Small batch (1 cup) | 2 minutes | Temperature of water | Clumping of dry powder |
| Medium batch (3 cups) | 5 minutes | Mixing speed | Uneven consistency |
| Large batch (1 gallon) | 15 minutes | Vessel surface area | Separation of layers |
Cold water increases the viscosity of the liquid phase, which may change how the mixture feels during initial incorporation.
If the material stays liquid even after you hit it, you have likely added too much water. You can fix this by leaving the container open for an hour to let some moisture evaporate or by adding more cornstarch in small, measured amounts.
Avoid the common mistake of dumping large scoops of powder to thicken a soupy mixture. This creates dense, dry pockets that refuse to hydrate. Instead, sift the powder through a fine-mesh strainer while stirring constantly. If the mixture remains thin after adding more than two extra tablespoons, stop. You have exceeded the saturation point, and further additions will only result in a brittle, crumbling mess.
Identifying the solid state
You can confirm the material is working by performing a simple “impact test.” If you punch the surface of the mixture with a closed fist, it should feel firm and resist your hand.
If your hand sinks into the mixture upon impact, the ratio of solid to liquid is too low. You can also try to roll a small amount into a ball; it should hold its shape while you apply pressure but melt into a puddle the moment you stop.
The National Institute of Standards and Technology explains that the rheology of complex fluids depends on these internal structural changes under shear stress. When the mixture is in its “solid” state, it won’t splash or spray even if you hit it with significant force. This property makes it a fascinating subject for studying how microscopic particles create macroscopic changes in physical behavior.
Common errors in handling
- Using too much liquid: This prevents the particles from forming the internal structure needed to resist force, resulting in a simple, runny liquid. Always start with less water than you think you need and add more only when necessary to reach the correct consistency.
- Mixing too slowly: This fails to engage the shear-thickening property of the material, making it difficult to judge if the ratio is correct. You must use quick, decisive movements to test the material’s resistance, as slow movement will always result in a fluid-like feel.
- Ignoring evaporation: Over time, the water in your mixture will evaporate, leaving you with a dry, cracked powder. Keep your container tightly sealed when you aren’t actively using the material to maintain the specific balance required for the dilatant effect to work.
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Frequently Asked Questions
Can I make dilatant materials with ingredients other than cornstarch?
Yes, you can use other fine powders like silica or certain types of starch mixed with water or oil to achieve similar effects. The key is to have a high concentration of solid particles that can jam together when force is applied. While cornstarch is the easiest for home use, industrial applications often use specialized polymers or synthetic particles designed to trigger this response at specific pressure levels.
Is it safe to touch these materials?
Yes, these mixtures are generally safe for skin contact, especially when made with food-grade cornstarch and water. They’re non-toxic and don’t cause chemical burns or irritation. However, you should avoid getting the mixture in your eyes or mouth, as it’s meant for tactile exploration rather than consumption. Always wash your hands thoroughly after playing with the substance to remove any residue from your skin.
Why does the material turn back into a liquid?
The material returns to a liquid state because the particles only jam together while there’s active, high-speed force pushing them into each other. Once that external energy stops, the particles are no longer being forced together and can once again move freely in the liquid medium. This process is reversible and can be repeated indefinitely as long as the ratio of liquid to solid remains stable.
How long does the mixture last before it spoils?
The mixture lasts for 2 to 3 days when stored in a sealed container away from direct heat. Because it contains water and organic starch, it will eventually grow mold or develop a sour smell. If you notice any change in color or an unpleasant odor, discard the mixture immediately and prepare a fresh batch.
What happens if I put it in the freezer?
Freezing the mixture will turn it into a solid block of ice and starch, which ruins the dilatant properties. When it thaws, the texture will likely be uneven and separated, making it perform poorly compared to a fresh batch. If you want to keep the material for a long time, it’s better to store the dry powder and water separately and mix them only when you’re ready to use them.
Conclusion
The behavior of these materials demonstrates how simple physical interactions can produce complex results. By adjusting the concentration of your mixture, you can change how firm it feels under pressure. This hands-on experience provides a clear view of how particle physics influences the everyday world, even in a kitchen setting.
