What liquid is the most viscous? Viscosity measures a fluid’s resistance to flow. The higher the viscosity, the thicker the liquid. Honey, maple syrup and molasses are examples of liquids with high viscosity. Oils and glycerin also tend to be quite viscous. On the other end of the spectrum, water, vinegar and alcohol have low viscosity and flow more freely. But which liquid has the absolute highest viscosity? Let’s take a look at some of the most viscous liquids known to science.
Most Viscous Everyday Liquids
Here are some of the most viscous common household liquids, in decreasing order of viscosity:
– Peanut butter – Quite thick and sticky. Hard to pour smoothly.
– Honey – Very slow pouring. Tends to coat surfaces thickly.
– Molasses – Extremely dense and sluggish flow. Coats spoon or pour spout.
– Maple syrup – Flows slowly and tends to clump. High density.
– Corn syrup – Thick, sticky liquid. High resistance to pouring.
– Oil – More viscous than water. Coats surfaces. Slow drip.
– Ketchup – Needs to be shaken or banged to get it flowing from the bottle.
– Mustard – Sluggish flow. Tends to clump up. Resists spreading.
– Chocolate syrup – Dense and thick. Slow pouring.
– Glycerin – Coats surfaces and drips slowly.
So everyday thick liquids like honey, peanut butter and molasses have some of the highest viscosities, though none of them are record-breakers.
Laboratory Chemicals with Extreme Viscosities
To find liquids with the absolute highest viscosities, we have to look at specialized chemicals used in laboratories. These synthetic substances can achieve incredibly high viscosities. Here are some examples:
– Pitch – This tar-like substance is solid at room temperature but becomes fluid when heated. Its viscosity can be 100 billion times higher than water! Pitch is so thick it flows at a rate of just one inch per year.
– Polybutene – This viscoelastic polymer liquid can reach viscosities over 200,000 times higher than water. It appears solid when sitting but flows under pressure.
– Silicone oil – With viscosities of up to one million centistokes, silicone oils are often used as machine lubricants. They are slippery liquids that can also resist flow under pressure.
– Glycerol – Chemically similar to household glycerin, pure glycerol can reach viscosities of nearly 2,000 centipoise – over 1,500 times higher than water.
– Buckminsterfullerene – Solutions of this carbon molecule in benzene can achieve viscosities on the order of 18,000 centipoise.
World Records for Viscous Liquids
The most viscous liquid ever created in a lab is aerogel made of graphene oxide. This water-based gel was produced in 2019 by scientists at the University of California, Los Angeles. With a viscosity of one billion centipoise, it’s about 1 million times thicker than honey!
The previous record-holder for most viscous liquid was an aromatic organic compound called pitch MC6. In 2006, researchers at the University of New South Wales measured its viscosity at 100 billion centipoise. That’s 100 million times thicker than water – an incredible feat.
Other related record-holders for extremely viscous fluids include:
– Highest viscosity petroleum-based liquid – Pitch mesophase. Viscosity of 100 million centipoise. Synthesized at Mitsubishi Gas Chemical Company in 1993.
– Highest viscosity polymer – Polybutene. Measured at 225 billion centipoise. Achieved by Imperial Chemical Industries in 1993.
– Highest viscosity silicon oil – 10 million centipoise. Created by Shin-Etsu Chemical Co. Ltd in 2010.
So while common liquids like honey and peanut butter are quite viscous, advanced lab-made liquids hold the records for true extreme viscosity. The graphene aerogel created in 2019 stands as the world’s most viscous liquid known.
What Makes Liquids Viscous?
Now that we’ve looked at some extremely viscous liquids, what actually makes them so thick and resistant to flow? Let’s examine some of the key molecular factors that determine viscosity in fluids.
Molecular Bonds
Liquids with strong intermolecular bonds between their molecules tend to have higher viscosity. The more tightly bonded the molecules, the more resistant they are to sliding past each other under flow. Hydrogen bonding in water, for example, gives it a higher viscosity than liquid nitrogen which has only weak van der Waals bonds.
Molecular Weight
Large, heavy molecules can result in more viscous liquids. More massive molecules have stronger intermolecular attractive forces and more resistance to flow. Syrups like molasses and corn syrup contain large sugar molecules, contributing to their high viscosity.
Molecular Shape
Branched and complex molecular structures interfere more with flow than simple linear shapes. Compare straight chain oils with more complex oils containing ring structures. The irregular shapes make sliding past each other more difficult.
Temperature
Viscosity decreases exponentially with increasing temperature. As liquids get hotter, their molecules have more thermal energy to overcome the intermolecular forces resisting flow. So heating a liquid drops its viscosity.
Dissolved Particles
Suspended particles in colloidal dispersions and solutions can substantially increase viscosity. Larger particles that impede flow have a greater thickening effect. Tomato ketchup loaded with starch and polysaccharides becomes more viscous.
Polymers
Polynomial liquids like molten plastics have long chain-like molecules that tangle together, creating high drag and viscosity. Polymer solutions like polybutene become extremely viscous even at low concentrations. The long polymer chains strongly resist flow.
So in summary, strong intermolecular bonding, heavy molecules, complex shapes, low temperatures, particles in solution, and polymers all contribute to higher viscosity in liquids. These effects help explain why substances like pitch and graphene aerogel set world records.
Measuring Viscosity
To systematically compare the viscosities of different liquids, we need some consistent methods of measurement. There are several standard techniques used to quantify viscosity in fluids.
Capillary Viscometers
This common lab instrument measures viscosity by timing how long a liquid takes to flow through a narrow tube. The slower it flows, the higher the viscosity. Capillary tube viscometers can handle viscosities up to 100,000 centipoise.
Falling Sphere Viscometers
This measures viscosity by dropping a ball bearing into a liquid and timing how long it takes to fall and reach terminal velocity. Viscous liquids slow the descent more. Good for highly viscous polymers up to 10 million centipoise.
Rotational Viscometers
These spin a cylinder within the test liquid to induce flow. More viscous liquids apply greater drag. Can handle up to millions of centipoise.
Vibrating Viscometers
These measure damping of an oscillating probe’s movements by the viscosity of the surrounding liquid. Good for curing plastics with changing viscosity.
Saybolt Viscometers
Measures how long a fixed volume of liquid takes to flow through an orifice. Widely used in the petroleum industry.
Ostwald Viscometers
Times flow between two marks of a fixed volume of liquid. The classic viscometer design with U-shaped glass tube.
So viscometers apply various principles of flow and drag to quantify viscosity. They give numerical viscosity values that help identify world record liquids.
Viscosity Units
With so many types of viscometers, how do we compare viscosity measurements? There are a number of standard units used to report liquid viscosity:
Poise (P)
The basic SI unit of viscosity in the centimeter-gram-second system. Water has a viscosity of about 0.01 poise at room temperature.
Centipoise (cP)
Viscosity measured in centipoises. Water is about 1 cP. Honey ranges from 2,000-10,000 cP.
Centistokes (cSt)
Another common metric equal to centipoises divided by density. About the same numeric value as centipoise.
Square Millimeter per Second (mm2/s)
The SI derived unit of kinematic viscosity. Around 1 mm2/s for water.
Saybolt Universal Seconds (SUS)
Saybolt viscometer time required for 60 ml to flow through a tube. Used for petroleum-based liquids.
Redwood Seconds (deg)
Saybolt system for certain oils based on amount flowing in 50°C temperature bath.
Viscosity ranges from 1 cP for water to billions of cP for ultra-thick liquids. Converting between units helps relate measurements.
Viscosity Conversion Table
| Centipoise (cP) | Centistokes (cSt) | mm2/s | Poise (P) |
|---|---|---|---|
| 1 | 1 | 0.01 | 0.01 |
| 10 | 10 | 0.1 | 0.1 |
| 100 | 100 | 1 | 1 |
| 1,000 | 1,000 | 10 | 10 |
| 10,000 | 10,000 | 100 | 100 |
| 100,000 | 100,000 | 1,000 | 1,000 |
So 100 cP equals 100 cSt, 1 mm2/s, and 0.1 P. This helps relate different viscosity units.
Effects of Viscosity
Now that we understand how liquids become viscous, let’s look at some of the key effects of high viscosity:
Flow Rate
Viscous liquids flow more slowly. Thick syrup flows far slower than water. High viscosity resists rapid flow.
Pouring Ability
The thicker the liquid, the harder it is to pour smoothly. Highly viscous liquids ooze and blob out. Low viscosity liquids pour neatly.
Spreadability
Viscous liquids like honey spread slowly. They coat surfaces thicker than less viscous liquids like alcohol.
Spraying Ability
Low viscosity liquids spray easily by breaking into fine droplets. Highly viscous fluids spray poorly or just ooze out.
Mixability
Thin liquids blend together easily. Viscous liquids tend to stay separated and are hard to mix.
Particulate Suspension
High viscosity liquids can suspend larger solid particles. Lower viscosity lets particles settle out.
Clinging Ability
Viscous liquids cling tenaciously to surfaces. Low viscosity liquids drain off easily.
Foaming
Forming foam requires viscosity. Thin liquids cannot trap bubbles. But viscous ones can create thicker, more stable foams.
Spattering
Drips of viscous liquid spatter less and run together more. Low viscosity drips spatter apart easily.
So viscosity has many impacts on liquid behavior that are important in different applications.
Applications of Viscous Liquids
Let’s examine some of the uses that viscous liquids are well suited for, due to their specific properties:
Foods
Viscous liquids like honey, condiments, and syrups allow flavorful coatings on foods. Their thickness carries more taste to the palate.
Cooking
Thick sauces cling to food better than thin ones. Viscous liquids also aid mixing and suspension in batters and doughs.
Medicines
High viscosity allows controlled dosing and coating of mouth and throat with syrups. It prolongs effectiveness.
Cosmetics
Lotions and creams need viscosity to cling to skin rather than drip off. It helps spread coverage evenly.
Coatings
Varnishes, paints and glues need viscosity to adhere and self-level on surfaces before hardening.
Lubricants
Oily lubricants require high viscosity to stay between surfaces. Low viscosity would let them drip away.
Shock Absorbers
Hydraulic fluid viscosity converts kinetic motion into heat to dampen shocks. Thin fluids couldn’t absorb energy well.
Molded Plastics
Viscosity allows molten plastics to flow and solidify in molds before becoming too rigid.
So viscosity is useful any time liquids need to coat, suspend, flow, cling or dissipate energy in a controlled way. It serves many key purposes.
Conclusion
In summary, while household liquids like honey and peanut butter are quite viscous, lab-made chemicals like graphene oxide hold the records for extreme viscosity. Molecular bonds, weight, shape, temperature, particles and polymers determine viscosity. Standardized instruments measure viscosity in units like centipoise and centistokes. Effects include flow rate, pouring, sprayability, mixing, clinging and foaming. Viscous liquids have diverse uses from foods to cosmetics to manufacturing. So while we experience viscosity daily, the science of truly understanding viscosity is complex and fascinating.
