Examples Of Non Newtonian Liquids

Exploring the Wonderful World of Non-Newtonian Fluids: Everyday Examples and Scientific Explanations

Non-Newtonian fluids are fascinating substances that defy the simple rules governing typical liquids like water or honey. Unlike Newtonian fluids, whose viscosity (resistance to flow) remains constant regardless of the applied force, non-Newtonian fluids exhibit a changing viscosity depending on the shear rate or stress applied. This means their behavior can dramatically alter depending on how you interact with them – a gentle touch might yield a liquid-like consistency, while a forceful impact could make them behave like a solid. This article will delve into various examples of non-Newtonian liquids, explaining their properties and underlying scientific principles. We'll uncover the magic behind their unique behavior and explore their diverse applications.

Understanding the Basics: Newtonian vs. Non-Newtonian Fluids

Before diving into examples, let's clarify the difference between Newtonian and non-Newtonian fluids. A Newtonian fluid follows Newton's law of viscosity, meaning its viscosity is independent of the shear rate. Think of water: pouring it gently or vigorously doesn't alter its fluidity. Its viscosity remains constant.

In contrast, a non-Newtonian fluid displays a viscosity that changes with the applied shear rate or stress. This change can be either shear-thinning (pseudoplastic), shear-thickening (dilatant), or exhibit other complex rheological behaviors.

• Shear-thinning (Pseudoplastic): The viscosity decreases as shear rate increases. Imagine ketchup: it's thick in the bottle, but once you shake it vigorously (applying high shear rate), it flows much more easily.
• Shear-thickening (Dilatant): The viscosity increases as shear rate increases. This is less common but equally fascinating. Imagine cornstarch mixed with water: gently stirring feels liquid-like, but a quick punch or forceful impact makes it solid-like.

Examples of Non-Newtonian Fluids in Everyday Life

The world around us is full of surprising examples of non-Newtonian fluids. Let's explore some common and less-common instances:

1. Oobleck (Cornstarch and Water Mixture): This is perhaps the most well-known example. Mixing cornstarch and water in the right proportions (roughly 1:1 or 1.5 parts cornstarch to 1 part water) creates a fascinating substance. Gentle stirring reveals its liquid-like nature, but a sudden punch or impact makes it momentarily solid. This is because the cornstarch particles have time to rearrange themselves under slow stresses, but under rapid stresses they lock together, increasing resistance to flow.

2. Ketchup: Ketchup is a classic example of a shear-thinning (pseudoplastic) fluid. It's thick and resists flowing when undisturbed, but shaking or stirring dramatically reduces its viscosity, allowing it to pour easily. This is due to the complex interactions between the tomato particles, water, and thickening agents.

3. Blood: Human blood, while vital, is a non-Newtonian fluid, exhibiting shear-thinning behavior. This is crucial for its efficient flow through blood vessels of varying diameters. At low shear rates (like in smaller capillaries), its viscosity is higher, ensuring proper blood flow. At higher shear rates (like in larger arteries), its viscosity decreases, facilitating smooth blood circulation.

4. Toothpaste: Like ketchup, toothpaste is a shear-thinning fluid. Its viscosity decreases with increasing shear rate, making it easy to squeeze from the tube but resisting immediate flow. This is achieved through the mixture of various thickening agents and other ingredients.

5. Quicksand: Quicksand is a natural example of a shear-thinning fluid. While often depicted dramatically in movies, the danger of quicksand lies not in its ability to "suck" you in, but rather in its rapid loss of viscosity under stress, making escape difficult.

6. Honey: While often considered a simple viscous liquid, honey demonstrates a slight non-Newtonian behavior, showing shear-thinning properties. Its viscosity reduces slightly at high shear rates.

7. Paint: Many paints are designed to be shear-thinning fluids. This property enables easy brushing and spreading, but once applied, the paint retains its viscosity to prevent dripping or running.

8. Mayonnaise: Mayonnaise is another example of a shear-thinning fluid. Its viscosity significantly reduces under shear stress, making it easily spreadable.

9. Molten Chocolate: The viscosity of molten chocolate is affected by factors such as temperature and shear rate, exhibiting non-Newtonian characteristics. This influences how it flows and behaves during production and consumption.

10. Silly Putty: This classic toy is a polymer that demonstrates both elastic and viscous properties, behaving as a solid under sudden stress but exhibiting viscous flow under slow stress.

The Science Behind Non-Newtonian Behavior: A Deeper Dive

The non-Newtonian behavior of these substances is due to complex interactions at the microscopic level. Here's a closer look:

• Particle Interactions: In fluids like Oobleck, the cornstarch particles act as individual units when under low shear stress, allowing the fluid to flow. However, under high shear stress, the particles collide and interlock, forming a temporary network that resists flow, giving it the solid-like characteristic.

• Polymer Chains: In polymers like Silly Putty, the long polymer chains become entangled. Under slow deformation, the chains can slide past each other, allowing viscous flow. However, under sudden stress, the chains get momentarily locked, leading to a more solid-like response.

• Hydrogen Bonding: In many non-Newtonian fluids, hydrogen bonding plays a role in viscosity change. The strength and number of these bonds can be affected by shear stress, leading to alterations in the fluid's viscosity.

• Colloidal Suspensions: Many non-Newtonian fluids are colloidal suspensions. These suspensions involve particles dispersed in a liquid medium. The interaction between these particles, the liquid, and any applied forces dictates the overall rheological behavior.

Applications of Non-Newtonian Fluids

The unique properties of non-Newtonian fluids make them incredibly useful across various fields:

• Engineering: Non-Newtonian fluids are used in various engineering applications, including designing shock absorbers, improving drilling mud in oil extraction, and creating protective coatings.

• Medicine: The rheological properties of blood are crucial in understanding and treating circulatory diseases. Non-Newtonian fluids are also used in drug delivery systems and tissue engineering.

• Food Industry: Many food products are non-Newtonian fluids, and understanding their rheological behavior is essential for optimizing processing and texture.

• Cosmetics: Many cosmetic products, such as lotions and creams, are formulated as non-Newtonian fluids for optimal application and feel.

• Sports: Certain sports equipment utilize the properties of non-Newtonian fluids for improved performance, such as specialized materials for shock absorption in sports gear.

Frequently Asked Questions (FAQ)

Q: Is quicksand truly as dangerous as portrayed in movies?

A: No. While quicksand can be hazardous, it's less dramatic than often depicted. The main danger is becoming trapped, but the risk of being "sucked under" is minimal. The shear-thinning properties make it difficult to escape, but with calm movement, one can often free themselves.

Q: Can I make Oobleck at home?

A: Absolutely! It's a simple and safe experiment for all ages. Just mix cornstarch and water until you achieve a consistency that’s both liquid-like and solid-like depending on the stress applied.

Q: What are some other examples of non-Newtonian fluids?

A: Many other substances exhibit non-Newtonian behavior, including some types of mud, certain polymer solutions, and specialized industrial fluids used in various manufacturing processes.

Q: How is the shear rate measured?

A: Shear rate is typically measured using rheometers, sophisticated instruments that apply controlled shear stress and measure the resulting flow behavior.

Conclusion: A World of Non-Newtonian Wonders

Non-Newtonian fluids are more than just intriguing scientific curiosities. They are essential materials with diverse applications across numerous fields. From the everyday simplicity of ketchup to the complex mechanics of blood flow, understanding the behavior of these fascinating substances expands our comprehension of the world around us. Exploring these materials provides a tangible and engaging way to learn about fluid dynamics and the importance of microscopic interactions in determining macroscopic properties. The next time you encounter a seemingly simple fluid, remember the complexity and surprising potential hidden within the world of non-Newtonian liquids.