Adhesive bonds are comprised of physical substances known as matter. All physical substances are matter that occupy space and contain mass. At this physical level, the smallest useful chemical component is the atom. Atoms are the fundamental chemical units of matter. Different types of atoms are classified as elements and these atoms can combine compounds, molecules, polymers, minerals, metals, or many other materials used in adhesive bonding.
Learning about atoms, elements, and compounds provides a foundation for understanding what makes an adhesive bond effective. This foundational knowledge will form the building blocks to determine why silicone sealant adheres strongly to clean glass but poorly to oily plastic. Similarly, an epoxy will be effective when applied to prepared steel but ineffective when applied over rust. The adhesive is the bonding agent, while the substrate refers to the materials being joined.
Why are Atoms and Compounds Important in Adhesive Bonding?
The effectiveness of an adhesive bond is determined not only by the chemicals in the bonding solutions but also by the processes that occur at the bonding interface. The interface is the space where the adhesive contacts the substrate. There are various types of substrates which may be made from metal, glass, wood, plastic, concrete, ceramic, rubber, composite material, or even a secondary adhesive. Within this interface, atoms and compounds are arranged in a particular way and may include oxides, oils, moisture, dust, salts, plasticizers, corrosion products, coatings, mold-release agents, and surface treatments. As a result, the chemical composition of the interface influences whether the adhesive can wet, attract the surface, chemically react with it, and remain intact over time.
Therefore, bonding science is not only about adhesives and sealants but also about how chemical interactions take place inside bonding zones. For instance, bonding aluminum doesn’t simply involve the aluminum itself; the surface oxidizes, causing the adhesive to interact primarily with aluminum oxide and any surface contaminants. Consequently, we can infer that adhesives bond to the material that is present on the actual surface and not to the material underlying it.
What is Matter?
Matter refers to the physical world, meaning anything that has mass and occupies space. Types of matter you may encounter in bonding applications include liquid adhesives, solid substrates, gaseous moisture or solvent vapors, cured polymer networks, glass, rubber, metal surfaces, wood fibers, concrete minerals, and fillers and pigments.
Matter is described as being a solid, liquid, or gas. Adhesives may move between states through their application, curing, or service. For example, a hot-melt adhesive is heated until it flows and solidifies as it cools. A solvent-based adhesive begins as a liquid fluid, and as the solvent evaporates, the adhesive becomes more concentrated, eventually transitioning to a solid polymer layer. All of these changes involve atoms, and the atoms don’t disappear, but their arrangement, movement, and chemical connections can change.
What is an Atom?
An atom is the smallest unit of an element that retains the chemical identity of that element. For instance, a carbon atom is still carbon because it contains six protons. Each atom consists of protons, neutrons, and electrons. Protons and neutrons are located in the nucleus, which is the center of the atom, while electrons are positioned outside the nucleus.
The number and arrangement of protons, neutrons, and electrons determine the identity and behavior of the atom. Electrons play a pivotal role in bonding science because they impact chemical bonding, electrical charge, surface interactions, molecular polarity, oxidation, intermolecular attraction, and chemical reactivity. The outermost electrons of an atom are referred to as valence electrons, which determine how atoms combine with one another.
Atomic Structure and Bonding Behavior
Atoms contain positive protons and negative electrons, and when these two particles are equal, the atom is electrically neutral. When an atom gains or loses electrons, it becomes electrically charged and is referred to as an ion.
Atoms can interact with each other by sharing electrons, transferring electrons, contributing electrons to a shared metallic structure, or by attracting nearby partial or full charges. These interactions help create substances used in bonding science applications such as adhesives, sealants, primers, coatings, metals, plastics, ceramics, and mineral-based substrates.
Through these atomic interactions, an atom’s inter-bonds and molecular structures influences properties such as the hardness, flexibility, chemical resistance, conductivity, melting behavior, surface energy, polarity, and reactivity of an adhesive bond.
What is an Element?
An element is a pure substance made from individual atoms that all have the same number of protons. The number of protons in an atom is called its atomic number, which determines the element’s identity.
For instance, hydrogen atoms contain one proton, oxygen atoms contain eight protons, carbon atoms contain six protons, aluminum atoms contain thirteen protons, and so on. You can view the full list of 118 confirmed elements on the periodic table.
Common Elements Found in Adhesives and Sealants
Adhesives and sealants contain numerous elements.
Carbon and Silicon:
Carbon forms the structural backbone of many organic adhesive polymers including epoxies, acrylics, polyurethanes, cyanoacrylates, and many rubber-based adhesives. Silicon is found in silicone adhesives, sealants, silane primes, and silica fillers. Silicon-based glues may be incredibly flexible, heat-resistant, and waterproof. Both have unique bonding properties that allow it to form strong, stable, complex network structures, which give the glue its body and strength
Hydrogen:
Hydrogen is present in most organic adhesive polymers and additives. When hydrogen is bonded to electronegative atoms such as oxygen and nitrogen, it may participate in hydrogen bonding. These intermolecular attractions can cause adhesion between the adhesive and substrate.
Oxygen and Nitrogen
Oxygen and nitrogen are relatively electronegative, which means they attract shared electrons within chemical bonds. This property makes them essential for creating polarity by forming positive and negative zones within a molecule. Oxygen is found in epoxies, polyurethanes, and acrylics, while nitrogen is found in superglues (cyanoacrylates) and polyurethanes.
Sulfur, Chlorine, and Fluorine.
Sulfur appears in some rubber-curing systems and in polysulfide sealants. Sulfur is especially useful in construction sealants because it may effectively cross-link polymer chains to create flexibility and toughness. Chlorine is effective for creating chemical resistance, flame retardancy, and stickiness to difficult plastics. Chlorine is found in solvent-based cements like PVC pipe glue. Likewise, fluorine is a tough substance because of how it interacts with carbon by ensuring it binds so tightly that nothing can interact with it.
Common Elements Found in Bonding Substrates
As mentioned before, the substrate is the material to which the adhesive bonds. There are many different types of substrates, some of which are:
Metals
Metals are a class of elements that may share similar characteristics, such as hardness, opacity, shiny luster, and thermal conductivity. Some common metals include iron, copper, aluminum, zinc, chromium, nickel, titanium, magnesium, and combinations of these elements.
Glass
Glass is generally composed of silicon and oxygen along with sodium, calcium, and other elements.
Plastics
Plastics are generally composed of carbon and hydrogen but may also contain amounts of oxygen, nitrogen, chlorine, and silicon.
Wood
Wood contains compounds created from carbon, hydrogen, and oxygen.
Concrete
Concrete contains calcium, silicon, oxygen, and other elements such as aluminum, iron, and hydrogen.
Ceramics
Ceramics comprise silicon, oxygen, aluminum, zirconium, and other elements.
Conclusion
By finishing reading this article, we can determine that the physical world is made up of atoms at the functional microscopic level. An element is a pure substance composed of one type of atom, and atoms of different elements combine to form compounds and molecules. Adhesives, sealants, and the substrates they join are all made from these atoms, elements, and compounds. When an adhesive contacts a substrate, their surfaces interact through intermolecular attractions, chemical bonding, mechanical interlocking, or a combination of these mechanisms. Once the adhesive is properly selected, applied, and cured, these interactions can create strong, durable, long-term bonds that keep the material joined together.
