Fundamental Properties of Adhesive Glue
Adhesive glue has been used for thousands of years to bond objects together. Glues come in many different forms, but their fundamental properties are the same.
There are two basic properties that adhesives must have to stick things together – cohesion and adhesion. These properties are influenced by many different factors, such as weight and situation.
Chemical bonding
Adhesive glue is a product that holds two surfaces together, such as glass and wood. They can be water-based or a solvent-based adhesive. They also require a process of curing to harden and hold the bond.
The strength of a chemical bond is determined by the difference in electronegativity between the atoms involved in the bond. The strongest bonds are ionic bonds, in which an atom loses an electron and gains a positive charge.
Covalent bonding is another type of bonding, in which the atoms involved in the bond do not have a large difference in electronegativity. These bonds are most common in organic compounds, and they are described by sigma and pi bonds (LCAO).
A chemical bond is an intermolecular force that connects atoms in molecules. The number of electrons participating in the bond is a multiple of two, four, or six, depending on the molecule.
Even numbers of electrons in the bond are more common than odd ones, because they enjoy lower energy states in the bonding orbital. For example, the carbons in benzene have 1.5 bonds, while the two atoms in nitric oxide have 2.5 bonds.
In addition to ionic bonding, there is also an intermediate category of bonding called polar covalent bonding. It is the most common form of bonding in most strong adhesives.
The most important difference between ionic and polar covalent bonding is that polar covalent bonding can be formed by the exchange of one or more electrons in the bonding orbital, while ionic bonding does not.
When polar covalent bonds are formed, there is an extra electron, which can be used to facilitate further bonding between the adhesive and the substrate. Typically, the extra electron is utilized to form a p-i bond between the two atoms of the molecule.
Often, these bonding mechanisms are combined with other methods of binding, such as van der Waals forces. This allows for the glue to be able to form a bond with its contact, while also ensuring that the glue is very durable. This is very useful for the production of products like paper, plastic, and rubber.
Van der Waals bonding
Van der Waals bonding is an electrostatic force that holds molecules together. The strength of the bonding depends on the number of electrons in each molecule and atom, as well as the concentration of charge density between molecules and atoms.
A weaker force than covalent and ionic chemical bonds, Van der Waals bonding is found in liquids, gasses, and solids. It is responsible for the bulk properties of substances, including their boiling points and melting points.
In the case of solids, Van der Waals forces tend to have lower melting points than covalent, ionic, or metallic bonds. These forces also help to maintain the tertiary structure of proteins.
The different types of Van der Waals forces include hydrogen bonding, dipole-dipole interactions, and London dispersion forces. Hydrogen bonding is a type of Van der Waals interaction that occurs between hydrogen molecules and other hydrogen-containing molecules in the presence of water.
Similarly, dipole-dipole interactions occur between polar molecules that have an unequal sharing of electrons. This causes a positive end of one polar molecule to attract the negative end of another polar molecule. This attraction is referred to as a dipole moment and it is important for the chemistry of hydrogen.
These Van der Waals forces can be seen in graphite, which is arranged in several layers of thin sheets. The temporary dispersion of a carbon atom’s electrons between the layers leads to the formation of very large temporary dipoles that attract the opposite dipoles in the next sheet above or below them.
When these van der Waals intermolecular forces are combined with the primary bonds of atoms and molecules, they form an attractive bond. The energies associated with van der Waals forces are much smaller than the energy associated with ionic adhesive glue or covalent bonds, but their effect can be very large when many atoms and molecules are involved.
Van der Waals forces have been shown to be essential in geckos, as they use them to stick on surfaces and climb walls. They have setae on their feet, which help them to grip very smooth surfaces such as glass. Attempts are being made to develop synthetic “gecko tape” that could harness the power of these forces and make climbing easier for humans.
Moisture aided diffusion
An adhesive glue is a substance that binds together dissimilar materials. It is used in construction, packaging, woodworking footwear, and automotive industries. It also helps to create a sealant that is resistant to moisture and the elements.
Adhesives are usually formulated from natural polymers such as dextrins, starches, and protein sources, or synthetic polymers that are soluble in water. They can also contain a hardener or solvent to promote or control curing.
A common method of bonding adhesives is the use of heat. Many hot melt adhesives are liquid at room temperature, but can become solid when heated to 275 degrees Fahrenheit. These types of adhesives are commonly used for applications that require a fast cure.
Another type of bonding method is moisture aided diffusion. This technique is often used in the construction industry to join metals to woods.
This process is very similar to chemical bonding, but it occurs on a much larger scale. Rather than just having two molecules of the same material bond, moisture aided diffusion involves the formation of a complex network of bonds between different atoms on both the surfaces being bonded and the adhesive itself.
The formation of the network can be caused by a variety of factors, including:
1. Moisture present on both sides of the surface being bonded and between the adhesive and the substrate being bonded. This enables the adhesive to enter the pores of the surface and form a bond there.
2. Trapped air between the adhesive and the substrate impedes the ability of the adhesive to wet the surface, which can result in interfacial failure.
3. Various other physical and chemical processes can help to speed up the drying time of an adhesive.
4. Adhesives can be cured by either evaporation or by chemical reaction.
5. A solvent can be added to the adhesive before it is applied, which can help to accelerate the curing process.
6. There are also special adhesives that can be cured by UV light.
These adhesives are often referred to as UV-cure glues because they can be cured by exposure to UV rays. They are generally transparent and can be used to bond translucent materials to themselves or to other materials.
Electrostatic bonding
Electrostatic bonding is a adhesive glue type of adhesive glue that can be used in many electronic applications. This adhesive glue is a strong polymer that can be used to attach two different materials together without the need for high heat or chemicals.
According to GMI’s Doyle, “For an adhesive to form a bond with a substrate, some type of interaction must occur between the adhesive and the surfaces being bonded.” This can include mechanical, physical adsorption or chemisorption. Fabrication techniques may change how much of this mechanism is involved but do not affect it to a significant degree.
Another important component of adhesive glue is the ability to conduct electricity. This can be achieved through the addition of inorganic conductive fillers or metallic particles to the resin base. These particles can be silver, copper, nickel or graphite and can be used to conduct electricity through the adhesive.
The electrical properties of adhesive glue can be customized for a wide range of application needs. For example, it can be formulated for resistance, conductivity and a variety of environmental stresses including shock and moisture.
In addition, adhesive glue can be modified to accommodate metallization options and contact pad pitch in electronic packaging. These changes are made via the chemical reaction of the conductive particles within the adhesive matrix.
These modifications are usually designed to increase the strength of the conductive glue and make it more suitable for use in harsh environments. They also improve the dimensional stability of the conductive adhesive and allow for greater ease in handling and dispensing.
A strong, reliable bond is essential in electronics, especially when the parts must withstand heavy use and temperature extremes. This is why the choice of adhesive glue is so crucial for a successful assembly.
