Mix, Crush, Shear: The Tools of Mechanochemistry
Discover how old techniques can produce greener, cleaner new things
ReadLatex mixers and stirrers (circa 1949) by Naval Air Experimental Station and United States NavyScience History Institute
Do you recognize any of these mixers?
In our kitchens, we know that a blender is not good for mixing bread dough. And you can’t use a stand mixer to make a milkshake. Mixing things at different speeds, or with differently shaped stirring implements, produces different effects.
But guess what? The mixers in this photograph are also a part of science’s history. They were used to test different mixing techniques on formulations of latex at the United States Naval Air Experimental Station around 1949.
Mechanochemistry
Chemists have used some surprising tools to learn how molecules are affected by mechanical actions like mixing, crushing and shearing.
This approach, called mechanochemistry, can lead to ways to make products that use less energy, require fewer toxic chemicals, and reduce waste.
Part 1: Mixing
Mixing seems simple—just stir things together. But take a closer look.
Fred W. Skirrow and Henry L. Heathcote Mixing a Solution (Circa 1900)Science History Institute
Chemical engineers know mixing different substances just right can be challenging. Chemists study mixing to learn how collisions, force, and pressure affect molecules.
Chemigum
During World War II, high flying warplanes pushed natural materials to their limits. Chemists were asked to develop synthetic rubbers that could better withstand temperature changes and maintain a seal at higher pressures.
Banbury Mixer in the Rubber Compounding and Processing Laboratory (Circa 1949) by Naval Air Experimental Station and United States NavyScience History Institute
Banbury mixer
One tool used in rubber research was the Banbury mixer. It controlled heat and pressure so molecules could form chains called polymers.
But scaling up a reaction from the lab to production was far from straightforward, as chemist Herman Schroeder told an oral historian.
James Mack and his Research TeamScience History Institute
Mechanocatalysis
In 2009, University of Cincinnati chemist James Mack developed a new way to start chemical reactions: mechanocatalysis. His team mashed together powdered chemicals with metal balls that catalyzed the reaction. As the precursors don’t have to be dissolved, there were no solvents to dispose of afterwards.
Resonant acoustic mixer
Chemists today are carrying forward mechanocatalysis research using a new mixing tool: the Resonant Acoustic Mixer. It doesn’t have blades or a dough hook. It uses focused sound waves to create vibration that brings materials into physical contact.
In one experiment, researchers used a resonantacoustic mixer and mechanocatalysis to make the medicine rufinamide. Focused sound waves rapidly mixed precursor chemicals in the presence of a copper catalysis, triggering a reaction without the use of solvents.
Part 2: Crushing
Like mixing, crushing is another mechanical process that can change chemistry.
Mortar and Pestles (After 1868–Before 1944)Science History Institute
The tried-and-true pestle
Chefs crush garlic to release its full flavor. Mining companies crush ore to release metals. Chemists have long used pestles to crush materials to create more surface area, thus speeding reactions.
Pages 19 and 20 from "Zinc: A Mine to Market Outline" (Circa 1961) by American Zinc InstituteScience History Institute
Ball mills: high-performance pestles
Mining companies have long used ball mills as the first step in extracting metals from rock. Tough spheres crash together to break up materials loaded into a sturdy, rotating drum. The zinc used to make a penny probably encountered a ball mill like this one.
Surfactants
Once a metal ore is crushed, industrial chemists use surface-active substances—or surfactants—to separate valuable metals from excess rock. In the flotation process, metal-bearing ore particles float on acidic bubbles, while non-metallic material settles away.
The Rehbinder Effect
Petr Rehbinder was an early leader in the study of surfactants. He discovered that some substances break much more easily when interacting with particular liquids.
In 1968 he co-organized a symposium that marked the emergence of mechanochemistry as a field of research.
Kathleen Floyd and Ball Mill (2025-04)Science History Institute
From the mine to the lab
Researchers today use ball mills to understand how mechanical force can be used to initiate chemical reactions. This may lead to advances in chemical processes that use less energy or do not require toxic solvents.
A Custom Smasher: The Controlled Force Reactor (2025)Science History Institute
The Controlled Force Reactor combines a finely controlled ball mill with special sensors that measure what’s going on inside the reaction chamber. Chemists use this tool to understand exactly how crushing causes chemical changes.
Part 3: Shearing
Shearing is a kind of mechanical action that may be less familiar than mixing and crushing. For scientists, shearing is what happens when two materials slide past each other. It’s central to tribology—the study of friction and lubrication.
Reducing friction means it takes less energy to do work
The Italian artist, engineer, and polymath Leonardo da Vinci constructed equipment to measure the friction between two blocks of wood sliding past each other.
Contemporary tribologists have recreated Leonardo’s work using pictures from his notebooks. They have concluded that Leonardo was not just a theorist—he likely worked with the tools he drew in the Codex Arundel.
Hollywood (1936) by Alfred EisenstaedtLIFE Photo Collection
Keeping the world running smoothly
More recently, understanding friction helped the spread of cars and airplanes in the 20th century. Mechanical engineers use tribometers to evaluate new kinds of grease and motor oil additives, part of the unseen work scientists and engineers do.
Today, chemists study friction using tribometers
They can measure the shearing forces that affect the “mouthfeel” of foods and the “skin feel” of lotions and shampoos. Or they can show how friction interacts with motor oil additives to build protective layers on metal parts.
Measuring Friction with the Tribometer (2025)Science History Institute
At the University of Pennsylvania, researchers are trying to turn the mini-traction machine into a more general tool for understanding mechanochemical processes.
Meet the Atomic Force Microscope (2025)Science History Institute
While the mini-traction machine measures shearing forces at the macro level, researchers can also study the effects of shearing at the level of tens to thousands of atoms. Atomic force microscopes can measure incredibly tiny shearing forces.
Conclusion
While mixing, crushing, and shearing are old practices, used for many purposes, there is still much we can learn from studying them. When scientists use surprising tools to study these processes, we can discover new and better ways to make the materials we need.
Written and Curated by Roger Turner
Edited by Jesse Smith
Video Production by Matthew Lorenz
Additional Video by Francesca Antillon
Digital Design by Clare Hirai
Scientific Advice by Dr. Robert Carpick, Will Opirsu, and Pezhman Palahang, University of Pennsylvania; and Dr. James Batteas, Dr. Francesca Antillon, and Dr. Emmanuel Nwoye, Texas A&M University
Special Thanks to Resodyn Acoustic Mixers
Funding for this exhibit was provided by the Center for the Mechanical Control of Chemistry under NSF Grant #CHE-2303044, and Texas A&M University.
