angle bead

What is the difference between surface free energy and surface energy? In the final analysis, this is a purely semantic question. Surface free energy is the free energy in a specific space (material surface). In the purest sense of thermodynamics, free energy refers to the energy that can be used to work, cause effects, and make something happen. The surface free energy is related to the energy that can be done on the surface of the material.
For manufacturers and anyone involved in adhesion, cleaning, bonding, coatings, inks and paint formulations, sealing, or any other process involving the interaction of surfaces with other surfaces or their environment, the surface free energy is usually shortened to just Surface energy.
Surfaces are critical to all the processes listed above, and even if they have a direct impact on the performance of product manufacturers in all industries, they are often not measured and therefore not controlled.
Controlling the surface in manufacturing refers to controlling the surface energy of the materials used.
The surface is composed of molecules that chemically interact with each other and the molecules that make up the surface of other materials with which they come into contact. In order to change the surface energy, it must be understood that those molecules can be removed by cleaning and treatment, replaced or otherwise manipulated to produce different levels of surface energy and achieve the desired results. In order to control the surface energy, it must be measured throughout the process of changing the surface chemistry to determine when and by how much. In this way, the precise amount of necessary surface energy can be obtained at the appropriate time during the adhesion or cleaning process.
To understand how molecules do the work of building strong bonds and chemically cleaning surfaces, we need to understand the attraction that pulls the molecules together and constitutes the total free energy of the available surface.
When we talk about the energy of the surface, we are talking about the ability of that surface to do work. Literally, this is the ability of the surface to move molecules-this movement requires energy. It is important to remember that a surface and the molecules that make up the surface are the same. Without molecules, there is no surface. If there is no energy, these molecules cannot complete the work of adsorbing on the adhesive, so there is no bonding.
Therefore, work is directly proportional to energy. More work requires more energy. Moreover, if you have more energy, your work will increase. The ability of a molecule to function comes from its attraction to other molecules. These attractive forces come from several different ways in which molecules interact.
Fundamentally, molecules interact because they have positively and negatively charged molecules, and they attract opposite charges between the molecules. A cloud of electrons floats around the molecule. Because of these constantly moving electrons, the molecule has a variable charge in a molecule of a given area. If all molecules have a uniform charge around them, no molecules will attract each other. Imagine two ball bearings, each ball bearing has a uniform distribution of electrons on its surface. Neither will attract each other because they both have a negative charge and no positive charge can be attracted.
Fortunately, in the real world, these electronic clouds are in constant motion, and there are areas with positive or negative charges at any moment. If you have two molecules with randomly charged electrons around them at any point in time, they will have a little attraction between them. The force generated by the random redistribution of positive and negative charges in the electron cloud around the molecule is called the dispersion force.
These forces are very weak. Regardless of the structure or composition of the molecule, there is a dispersion force between all molecules, which is directly opposite to the polar force generated by the structure of the molecule.
For example, the dispersion force is the only force that exists between nitrogen molecules. At room temperature, nitrogen is a kind of gas, because the dispersing force is too weak, it cannot resist thermal vibration even at the most moderate temperature, and it cannot hold the nitrogen molecules together. Only when we remove almost all the heat energy by cooling it to below -195°C does the nitrogen become liquid. Once the thermal energy is sufficiently reduced, the weaker dispersion force can overcome the thermal vibration and pull the nitrogen molecules together to form a liquid.
If we look at water, its molecular size and mass are similar to those of nitrogen, but the structure and composition of water molecules are different from those of nitrogen. Since water is a very polar molecule, the molecules will attract each other very strongly, and the water will remain liquid until the temperature of the water rises above 100°C. At this temperature, the heat energy overcomes the molecular With the polar forces held together, the water becomes a gas.
The key point to understand is the difference in strength between the dispersion force and the polar force that attracts molecules to each other. When we talk about the surface energy produced by these attractive forces, please keep this in mind.
Dispersed surface energy is part of the surface energy, which is generated by the dispersion of electron clouds in molecules on the surface of the material. The total surface energy is an attractive expression of the attraction of molecules to each other. Dispersed surface energies are part of the total energy, even if they are weak and fluctuating components.
For different materials, the dispersed surface energy is different. Highly aromatic polymers (such as polystyrene) have many benzene rings and relatively large surface energy dispersing components. Similarly, because they contain a large number of heteroatoms (such as chlorine), PVC also has a relatively large dispersed surface energy component in their total surface energy.
Therefore, the role of dispersion energy in the manufacturing process depends on the materials used. However, since the dispersion force hardly depends on the specific molecular structure, the way to control them is very limited.
The interaction of scattered electron deflection based on these fluctuations is not the only way for molecules to interact with each other. Due to certain structural features that create other attractive forces between molecules, molecules can interact with other molecules. There are many ways to classify these other forces, such as acid-base interactions, where molecules interact through their ability to accept or donate electrons.
Some molecules have structural features that produce permanent dipoles, which means that, in addition to the random dispersion of electrons around the molecule, some parts of the molecule are always more positive or negative than others. These permanent dipoles are more attractive than dispersive interactions.
Due to their structure, some molecules have permanently charged regions that are either positively or negatively charged. Polar surface energy is a component of surface energy, which is caused by the attraction of these charges between molecules.
We can easily concentrate all non-dispersive interactions under the protection of polar interactions.
The dispersion properties of a molecule are a function of the size of the molecule, especially how many electrons and protons are present. We do not have much control over the number of electrons and protons, which limits our ability to control the dispersion component of surface energy.
However, the polar component depends on the position of protons and electrons-the shape of the molecule. We can change the distribution of electrons and protons through treatment methods such as corona treatment and plasma treatment. This is similar to how we can change the shape of block clay, but it will always maintain the same quality.
Polar forces are very important because they are part of the surface energy that we control when we perform surface treatments. Dipole-dipole attraction is the cause of strong adhesion between most adhesives, paints and inks and surfaces. Through cleaning, flame treatment, corona treatment, plasma treatment or any other form of surface treatment, we can fundamentally increase the polar component of surface energy, thereby improving adhesion.
By using the same side of the IPA wipe twice on the same surface, only low-energy substances can be introduced onto the surface to unintentionally reduce the polar component of the surface energy. In addition, the surface may be over-treated, which volatilizes and reduces surface energy. When the surface is not produced at all, the polar component of the surface energy will also change. A clean storage surface attracts molecules in the environment, including packaging materials. This changes the molecular landscape of the surface and may reduce the surface energy.
We can hardly control the size of the dispersion. These forces are basically fixed, and there is little value in trying to change the dispersion force as a means of controlling surface quality to achieve reliable adhesion during the manufacturing process.
When we design or modify the surface, we are designing the properties of the polar component of the surface energy. Therefore, if we want to develop a surface treatment process to control the surface of the material, then we want to control the polar composition of the surface.
Surface free energy is the sum of all individual forces acting between molecules. There are some formulas for surface free energy. If we decide to treat all non-dispersive forces as polar forces, the calculation of surface free energy is simple. The formula is:
In the manufacture of reliable products, surface treatment, cleaning and preparation, the surface free energy is the same as the surface energy.
Due to the production requirements involved in various processes, such as the adhesion performance of the joint, the proper adhesion of the ink on the plastic or the coating performance of the “self-cleaning” coating on the smartphone screen, all depend on the control of the surface properties. Therefore, it is very important to understand the surface energy as a consequence of the manufacturing concept.
Surface energy comes from the different ways in which molecules attract each other. The polar interactions between molecules are the most important for the adhesion and cleaning process, because these molecular-level interactions are the molecular interactions that we can control most through surface treatment, grinding, sanding, cleaning, wiping or any other surface preparation methods .
Knowledge of polarity and dispersion composition and surface tension is very important for the development of adhesives, inks and coatings. However, for products manufactured using adhesives, inks, paints and coatings, we usually only need to pay attention to the polar component of the surface energy, because it is one that is affected by the manufacturing process.
Measuring total surface energy is a relatively complex and error-prone process. However, the contact angle of a single liquid like water is almost entirely determined by the polar component of the surface energy. Therefore, by measuring the angle produced by the height of a drop of water on the surface, we can know with amazing accuracy how the polar component of the surface energy changes. Generally, the higher the surface energy, the smaller the angle caused by the water droplets being so attracted and spreading or wetting. Low surface energy will cause water to bead and shrink into small bubbles on the surface, forming a larger contact angle. The consistency of this contact angle measurement is related to surface energy and therefore to adhesion performance, which provides manufacturers with a reliable and repeatable way to ensure the strength of their products.
To learn more about controlling the manufacturing process to achieve more predictable results, download our free e-book: Verify predictable adhesion in manufacturing through the process. This e-book is your guide to process monitoring using predictive analytics, a process that eliminates all guesswork about maintaining surface quality throughout the bonding process.