Mechanochemistry might be an entirely new topic for many of you. Don’t worry, we’ve prepared a handy mechanochemical glossary to help you get to grips with some of the most commonly used terms and concepts in this fascinating branch of chemistry.
Today’s article is the last in a series of four blogposts, our personal dictionary with terms arranged in alphabetical order, of course. This edition covers terms from S to Z. If you missed our three previous instalments, you can read them here, here and here.
Scale up
The process of increasing the size or capacity of a chemical production operation from a small, laboratory scale to a larger, industrial scale. It is crucial for moving from promising research to practical application. Scaling up requires adapting conditions, equipment and processes to ensure efficiency, safety and product quality. At IMPACTIVE, we take this very seriously, with a dedicated work package to do so: number five.
Shear force
The mechanical forces used in mechanochemistry can take many different forms. One of them is shear force —don’t mistake it with sheer force, this is much more nuanced! It is typically applied through grinding, milling, or rubbing actions that transfer the mechanical energy of surfaces in relative motion to the reactant compounds. In other words, shearing is what happens when two materials slide past each other. This type of force is particularly useful for initiating reactions in mechanochemistry.
Solid state
Matter can exist in several physical states, with three main ones: gas, liquid and solid. These states differ in the amount of energy present within their atoms or molecules. The solid state has the lowest energy of the three, resulting in particles that are closely packed together.
Solids have certain characteristics that makes them different from liquids and gases. For example, all solids can resist forces applied either perpendicular or parallel to their surfaces. Such properties depend on the nature of the atoms that form the solid, on the way those atoms are arranged, and on the forces between them. When the atoms are arranged in a well-ordered structure, the material forms a crystal; when they are not, an amorphous solid.
Solution-based chemistry
Solution-based chemistry refers to the practice of carrying out chemical reactions in liquid solutions. This is how chemistry has been traditionally working. In this approach, reactants are dissolved in one or more solvents, creating a reaction environment whose properties, such as the types and concentrations of ions or the nature of the solvent, can strongly influence reaction pathways and product formation. This method of doing chemistry relies on the use of solvents, which contribute significantly to the environmental impact of the chemical industry.
Solvent
A solvent is a substance, usually a liquid, that can dissolve other materials to form a homogeneous mixture in which the individual components are indistinguishable. This mixture is called a solution, and the material being dissolved is known as the solute. One characteristic of solutions is that the components generally do not react chemically with one another. Instead, the solvent molecules surround and attract the solute, helping it to distribute and stabilise evenly. Additionally, the formation of a solution often alters the physical properties of its components.
Solvent-free synthesis
As we said two definitions ago, traditional chemistry relies on solvents to conduct its reactions. In a solvent-free synthesis, these substances are not longer required. An example of this type of chemical synthesis is mechanochemistry, where reactions are carried out in the solid state by milling, crushing and shearing the different compounds involved. Solvent-free chemical syntheses offer the advantage of avoiding contaminant substances, which ultimately reduces the generation of waste that would otherwise need to be disposed of.
Spray drying
Spray drying is a method used in chemical synthesis that involves dissolving the compounds of interest in a minimal amount of solvent. The resulting mixture is then atomised into tiny droplets, which are rapidly dried using heated gas to isolate the new compound. An important feature of this method, particularly in the pharmaceutical industry, is that it can be used not only for chemical synthesis but also for process intensification. All components, including excipients and active pharmaceutical ingredients (APIs), can be combined and processed into what is essentially the final pharmaceutical formulation.
Tribochemistry
This interesting term was first proposed to describe the chemical and physico-chemical changes that occur in solid materials when they are exposed to mechanical energy. In other words, it refered to solid-state mechanochemistry. Now, tribochemistry has a slightly specific meaning. It describes a specialised area of mechanochemistry that focuses on chemical reactions happening between surfaces in contact, along with any lubricants or additives present, when they slide against each other. These reactions are triggered by friction, heat, and shearing forces.
Twin-screw extrusion
Mechanochemical techniques can take the most unexpected forms. The twin-screw extrusion method uses two co-rotating screws to process and extrude compounds. As the reactants travel along the screws, the spinning action grinds the molecules together. This triggers mechanochemical reactions in a continuous process. The advantage? There’s no need to stop the extruder to recover the materials. It can run for hours without interruption.
Waste
A general definition of waste could be something like: “discarded material as it is no longer useful or required, especially what remains after the valuable substances or parts have been removed”. But here we are thinking of one specific type of waste: solvents. The traditional way of doing chemistry relies heavily on solvents. Once a reaction has taken place, the solvents involved are no longer needed and must be disposed of. This is why traditional, solvent-based chemistry generates such large amounts of waste. And this is precisely why, in mechanochemistry, we work towards solvent-free chemistry.
X-ray diffraction
X-ray diffraction is a widely used analytical technique to study the chemical composition and crystalline structure of materials. More specifically, it provides information about crystal orientation, crystallite size, preferred orientation, and layer thickness. It works by directing an X-ray beam at the sample and measuring how the rays are diffracted. There are several variations of this technique, such as X-ray powder diffraction and single-crystal X-ray diffraction. Powder diffraction is used to study samples that are made up of many randomly oriented crystals, while single crystal diffraction is used to study samples that are made up of a single, oriented crystal.