Why does surfactant lower surface tension

They are amphiphilic molecules and are thus absorbed in the air-water interface. At the interface, they align themselves so that the hydrophobic part is in the air and the hydrophilic part is in water. This will cause a decrease in surface or interfacial tensions.

As said, surfactants are amphiphilic molecules that have hydrophobic and hydrophilic parts. The hydrophobic tail is a hydrocarbon, fluorocarbon or siloxane. Surfactants are typically classified based on their polar head as the hydrophobic tails are often similar. If the head group has no charge, the surfactant is called non-ionic.

If the head group has negative or positive charge, it is called anionic or cationic, respectively. If it contains both positive and negative groups, then the surfactant is called zwitterionic. Anionic and nonionic surfactants are by far the most used surfactant types in the industry. Anionic surfactant finds use especially in cleaning products like laundry detergents and shampoos. Nonionic surfactants on the other hand are often used as wetting agents and in the food industry.

Both cationic and zwitterionic surfactants are more for special use as they are more expensive to produce. Because of their amphiphilic nature, surfactants absorb at the air-water or oil-water interface.

At the interface, surfactants align themselves so that the hydrophobic part is in the air or oil and the hydrophilic part in water. The cohesive forces between the water molecules are very strong making the surface tension of water high. As surfactants absorb they break these interactions. Manufacturers need to acquaint themselves with these concepts because controlling surface quality through surface energy measurement of solid materials is the most predictive method of ensuring high performance bonds and coatings.

An important tool in our toolboxes for controlling surface tension is the class of chemical compounds known as surfactants. They are pretty much universally found in cleaning agents, coatings, inks, lubricants, adhesives, and cosmetics: one important characteristic of surfactants is that they can help dissimilar substances mix like oil and water. Surfactants are incredibly useful and beneficial Creating and maintaining chemically clean surfaces is a vital part of building reliable products in many instances.

For example, automobile engine blocks are assembled with silicone sealants. If the surfaces are not chemically clean before applying the sealant, the engine will leak oil onto your driveway. Chemical cleanliness of sealing surfaces can be achieved through carefully monitored and controlled aqueous cleaning processes.

These processes depend on surfactants to make contaminants soluble in the cleaning solution. However, if the surfactants aren't completely removed via a rinsing step, the end effect is that we have just replaced the original soils and contaminants with a new one that will also inhibit sealant adhesion: residual surfactant. Sometimes a chemically clean surface is all we need for manufacturing success.

However, with many applications, we need to further engineer the surface through surface treatment to obtain desirable properties like corrosion resistance or strong and durable adhesion of coatings or adhesives. The presence of residual surfactants on these surfaces can prevent successful surface treatment.

For inks, paints and adhesives to work properly they have to spread over the surface that they're applied to. This requires that the surface tension of the ink, paint or adhesive is lower than the surface energy of the substrate. This is just another way of saying that the molecules in the paint, adhesive or ink need to be attracted more strongly to the surface than they are to each other.

We can control the surface tension of a coating or adhesive by the addition of surfactants. Surfactants are directly related to surface tension and play a very important role in adhesion processes. But, how do they work and how can manufacturers make sure surfactants are doing their job without disrupting the work of creating chemically clean surfaces? By looking at what surfactants are intended for, their effect on surface tension and how to recognize when they are on our material surfaces, we can make use of these powerful manufacturing tools to create clean surfaces that can guarantee high-performing products.

A surfactant, at its most basic, is a substance that is designed to reduce the surface tension of a liquid. For many operations in manufacturing processes, it is necessary for a liquid to spread out and wet a surface.

Adding a surfactant to a coating or detergent lowers the surface tension of the liquid so it will flow more, covering the entirety of the surface. For instance, surfactants are often added to insecticides to ensure the substance fully spreads out over the entire surface of leaves instead of just a small portion of the plant.

This allows the insecticide to be maximally effective. As a reminder, surface tension is the attractive force of the molecules present at the surface of a liquid towards each other. Modifications to the surface tension of a liquid is one factor that helps determine the performance of a bond between a solid surface and a liquid. The most common material is platinum. Experiments conducted under controlled and inert atmosphere have shown that water indeed completely wets platinum.

However, many compounds found in the ambient air adsorb strongly on platinum, the effect is observable within minutes of flaming. Thus, the probe should be immersed in the measured liquid promptly after cleaning. When flame cleaned using a hot flame, the oxide layer is activated into a very hydrophilic state. It is more stable towards airborne contaminants than Platinum, but does passivate with time.

Therefore, proper flame cleaning procedures cannot be avoided. There are two sub-techniques of force tensiometry, namely the Wilhelmy and DuNouy methods. In the Wilhelmy method, the probe is held still in the interface, preferentially with the lower end level with the interface at far distance.

At this point there is no need for buoyancy corrections. Both so called Wilhelmy plates and rod shaped probes can be used to make the measurement. In the DuNouy maximum pull force method the surface tension is recorded as the probe is slowly withdrawn from the liquid. The probe is usually a DuNouy ring or a vertical rod. The movement of the probe advantageously provides a receding contact angle, which tends to be smaller than the resting contact angle. The drawback of the technique is the need to account for the negative buoyancy term corresponding to the point of maximum force where the probe is completely above the surface.

For thin rod probes the buoyancy term is relatively small and easy to correct for, while for rings the buoyancy term is significant and its calculation complicated by the cross-sectional shape of the ring.

Surface Tension What is surface tension Surface tension is defined as the work, dW, required to expand a surface by dA.