There glueone of the oldest and most useful inventions for humanity, accompanies us from the stone age and helps us to produce more resistant tools, Paste fabrics o construction materials, and even a Close wounds and cuts. What makes the hill more or less “sticky” are the strength of ties chemists Between the glue molecules and the material to be glued, the viscosity of the same glue and the ability of polymerizationthat is, to create longer and more stable molecules that keep our “art attack” together. From an early age we learn to use the glue, but we hardly stop to think what the “sticky” hill really makes it and why particularly effective with some materials are bad in other applications. These questions are, in reality, less trivial than one might think: still today the world of research studies hill to develop stronger, long -lasting or safe products to use.
What makes glue sticky: chemical ties and viscosity
Given the great differences between types of glue and materials to be glued, it is not surprising that there is no single mechanism At the basis of their “stickiness”. On a microscopic level, the matter is made up of atoms (iron objects, copper) or molecules: within the same material, the interactions between the various atoms and molecules that compose it are stronger, with covalent or ionic bonds between atoms that form complex molecules or ordered structures such as i crystalline reticols.
On the surface of the material instead, The interactions with the “external world” are much less strongdue to the presence of weak positive and negative electrical charges, such as Van der Waals’s forces, which we can compare the magnetic attraction between two magnets, but much weaker. What does this have to do with hill? Colle allow to fill the tiny spaces between the surfaces of two contact materials, eliminating the air remained in the interstices e greatly increasing the quantity of weak interactions and consequently the friction between the two parts.
To glue, however, another fundamental factor is the viscosity and the formation of ties between molecules of the glue itself. For example, we compare “the stickiness” of honey to that of water: both can fill the interstices between our fingers, but only honey “paste” them. This is due to interactions between honey molecules (mainly sugars), much stronger than those among the water molecules. Honey is more viscoustherefore it flows less easily, because it “attacks” to itself, as well as to our fingers. In most cases, however, these simple interactions are not enough.
The importance of polymerization and solvents
Many hill after application give life to polymerization processes, that is, a chemical reaction which, starting from many small molecules (monomers), leads to the formation of much longer molecules (polymers) and stablethen creating solid connections between the glued surfaces. This is the principle underlying the Cianoacrilati adhesives, compounds used in HOLDS INSTANTANE A FROW TRUST (like the superattack®), which polymerize and solidify in the presence of humidity in the air.
The reactivity with water makes cyanacrililated also suitable for medical use, as substitutes for surgical points or other sutures in emergency medicine: in contact with human fabrics, the hill polymer rapidly, closing the wounds. Attention: the hill for medical use are specific and of hospital relevance, while the municipalities with the instantaneous by the supermarket are produced very irritating, so don’t use them for “do it yourself” rescue. For any eventuality, it is always necessary to contact your doctor.
In other cases, for example for polymers dissolved in a solvent, it is theevaporation of the solvent itself to encourage the formation of the lattices between polymers: this is the case of vinyl gluea solution of polyvinilalcooli dissolved in the water. This very fluid glue works well with porous materials such as wood or paper: it comes easily absorbed And then it penetrates inside the materials. When the water evaporates, the glue drys out, By linking the materials, as a sort of “liquid spider web”.
Solubility in the water is also the reason why, in case you get dirty with vinyl glue, enough Simply wash your hands: an important feature that, combined with the non -toxicity of the material, made it one of the most used stickers in schools and for DIY.
A similar mechanism is the basis of the classics hot with hotother favorites of DIY: in this case, to “free” the polymers is simply the heating of gluewhich in liquid form can be applied on surfaces and partly penetrate porous materials. Cooling will lead tohardening of the glue, which still remains “flexible” and almost rubbery, a feature also useful for endure mechanical vibrations or stress. However, the process is totally reversible: a subsequent heating would make the gluing ineffective.
Colle from the Pietra Age to post-it
Colla is probably one of the older human inventions: archaeological finds dating back to the stone age, in Africa, show that the sapiens were able not only to exploit Esuded Resins (i.e. released already in liquid form, for example after breaking a branch) from the plants, but also to obtain some with processes of dry distillation from trees of Podocarpus.
For centuries, nature has always been the main source of glue: man has learned to exploit animal plants and tissues, such as the fish cartilage Or connective fabrics of horses or cattle, to produce substances capable of gluing materials such as wood. Modern chemistry has also marked the boom of synthetic products for hill obtained from oil or natural gaslooking for the best characteristics for each individual application.
Let’s think for example about the vinyl glue, Not irritating and relatively “weak” is excellent for gluing porous materials such as paper or wood. Or post-it®whose glue is contained in resin bubbles to “break” With light pressure, a feature that makes them easily detachable and reusable since not all glue is used for each “attack”.
