What is surface tension, and how does this affect my components?

Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension allows objects with a higher density than water, such as razor blades and insects (e.g. water striders), to float on a water surface without becoming even partly submerged.

There are two primary mechanisms in play. One is an inward force on the surface molecules, causing the liquid to contract. The second is a tangential force parallel to the surface of the liquid. This tangential force (per unit length) is generally referred to as surface tension. The net effect is that the liquid behaves as if its surface were covered with a stretched elastic membrane. But this analogy must not be taken too far, as the tension in an elastic membrane is dependent on the amount of deformation of the membrane, while surface tension is an inherent property of the liquid–air or liquid-vapour interface.

Surface tension exudes different properties depending upon whether it has a surface curvature, pressure differential, floating, and contact angle. All of these can now be identified and measured.

At a basic level, surface tension measurement uses three processes to ascertain the attractive forces generated by different molecules. However, dependent upon the materials, there can be up to 12 variations of that measurement process.

The printing industry initially developed surface tension measurement to measure print quality from printing plates to other surfaces. In its simplest form, inks were drawn onto a surface, such as paper. If they produced a solid line or dispersed into liquid bubbles, they showed their efficacy on that surface. Once identified, using the correct ink viscosity to deliver a clear print on that surface was achievable. A lot of trial and error would eventually yield a usable result.

The measurement is known as the Dyne Value or mN/m value. (Milli Newtons/metre).

Engineers soon recognised the importance of this form of measurement across all areas of modern manufacturing. They found that the molecular structure or composition of bonded substances is of far greater concern to the efficiency of the end product. They also found that surface tension is 99%+ dependent upon the chemical composition of the molecules present in the top 1-5 molecular layers of a substance’s surface. In summary, the molecules’ ability to adapt and reposition themselves plays a significant effect on the strength of the materials and the finished product

The downside to the measurement process has often been the instruments used. They can be large, unwieldy and limited in their scope. In addition, they require time, specialist knowledge, and the samples tested, most times sent off-site. However, advances in both science and computing are changing that measurement process slowly, and smaller devices such as the unique KRUSS MSA are slowly becoming available.

Understanding surface tension properties provide a huge benefit to all aspects of manufacturing. In its simplest form, the interaction between multiple surfaces differentiates between a quality product and a short term product. Therefore, knowing just how good the bonding is between the surface tensions of materials directly affects costs, quality management, productivity and profits.

Working within or above the current industry standards will help define your company’s position in the marketplace and directly affect revenue and profits.