When discussing enhanced materials we often use terms like “hydrophilic/hydrophobic” and “oleophilic/oleophobic.” Just what do these terms mean exactly? Let’s take a quick look.

• Hydrophilic − Refers to substances that absorb water. A hydrophilic substance will bond, on a molecular level with water.
• Hydrophobic − Refers to materials that will repel water.
• Oleophilic − Refers to a substance that absorb oils or nonpolar liquids.
• Oleophobic − Refers to a substance that repels oils or nonpolar liquids.
• Hygroscopic − Refers to the ability of a material to absorb humidity from the air. A hygroscopic substance will actively attract and absorb water, without bonding. (A hygroscope is an instrument that indicates changes in humidity.)

Water is itself hydrophilic (it mixes with more water easily) and oils or fats are generally hydrophobic and will separate from water, forming an oily layer.

Note: The suffix "philic" means loving or attracted to. The suffix "phobic" means fear or fearful.

There’s a lot more to learn, but this is certainly a useful place to start. If we can help you sort these terms out or provide information on how to modify materials to enhance (or suppress) any these characteristics, please do not hesitate to reach out to our experts.

It’s a back-to-basics question, but one that we are asked often. Surface treatments are generally separated into two categories: atmospheric and low-pressure (or vacuum). Both use energy to ionize gas and are very effective at altering the surface properties of materials. Both can also help you increase your manufacturing yield. Today we spotlight corona treatment:

Corona surface treatments work by forcing a gas (usually air) between two high-powered electrodes at a high rate of speed. As the air passes through the electrical discharge, it becomes ionized and, in the presence of ambient oxygen, forms chemically functional groups on the surface of a substrate. The functional groups that result from the process increase the surface energy on polymers and other materials.

Corona treatments (or atmospheric treatments) use standard electrical power, but have limited controls, such as the distance the material is held from the electrical discharge, and the speed at which the material passes through the active plasma. Corona is an excellent treatment solution for common plastic films, such as those used in packaging. Review the top 4 questions to ask when sourcing a surface treatment partner.

Advantages of Corona Surface treatment:

Corona treatments can treat large substrates very rapidly, and are effective at making many commodity-grade polymers wettable to facilitate the application of adhesives, paints, inks and tape.

Considerations of Corona Surface treatment:

Treatment lifespan

Treatment lifetime can be relatively short; minutes, hours or days depending on the substrate and the effectiveness of the treatment. However, this is a non-issue in applications where adhesives or paints are applied immediately after the treatment.

Heat distortion

Since the electrical discharge is quite hot, it’s critical to calibrate the speed at which the substrate passes through the plasma region. Also look at the distance between the substrate and the discharge. In cases where the speed is too slow or the distance too short, thermal distortion is likely to occur.

Uniform Coverage

Since only the area of the substrate that is passed through the plasma region is treated, surface areas may not be treated evenly. This is especially true when working with complicated geometries.

Ozone levels

Corona surface treatments generate high levels of ozone, so proper ventilation precautions must be taken.

Share your experience with corona treatment in the comments!

Up Next: Surface treatment Part II: Plasma treatment

Reading through some of our older posts, I noticed that we received some great feedback on our coverage of Plasma Surface Modification Improves Drone Aerodynamics. A topic that is still timely today. In this instance, our client needed to improve the bond strength on the wing edge of their drones. The end result after plasma treatment was a superior bond adhesion that excelled at resisting wind forces.

Today I wanted to review 3 key benefits of surface modification for all industries.

Plasma surface modification is often described as a low-pressure gas with electricity running through it. It contains ions, free radicals, excited molecules and UV light. When exposed to an energy source such as electricity or microwave, it becomes a mix of ions, free electrons and other types of molecular fragments. The resultant plasma treatment removes all traces of organic contamination. 

When properly applied, plasma treatment can:

• Microscopically modify the surface of a polymer substrate to improve mechanical bond strength without altering the haze, transmittance or clarity of the material 
• Clean surfaces to improve the surface wetting and adhesion of paints, coatings and markings
• Functionalize groups (carboxyl (HOOC-), carbonyl (-C=O-), hydroxyl (HO- and others) to the polymer substrate to significantly increase the surface energy for bonding; particularly in applications where aqueous-based adhesives require a bond strength that can’t be obtained with conventional cleaning techniques.

Surface modification can benefit industries ranging from medical and biotech, to electronics and even consumer goods. For additional benefits, get your free copy of our Surface Modification technical paper! Or just Ask an Expert for advice!

Measuring surface tension can be done quite easily in the lab with the use of a goniometer (or surface contact meter). In fact, this is a key service of TriStar’s Surface Modification Division. 

The process begins by first measuring the baseline contact angles to determine the right surface modification method. Since the surface tension of liquids and the surface energy of materials must be matched, we add a droplet of water to the component to get the best reading. 

The component is then placed in a vacuum plasma chamber, treated, and read again to measure tension changes. After plasma cleaning, components are much more accepting of secondary treatments such as adhesion, ink stamping, overmolding and more. If the surface energy of the material is too low, then the coatings will not flow well and fisheyes, pinholes, gaps, or air bubbles will form. If the material surface energy is too high, then paints, inks and other coatings may bleed or be difficult to control. So accuracy is key!

Here’s a chart to help you review the different variables of untreated polymers:

You might also want to check out this video for a demonstration (below), or feel free to reach out to the Surface Modification Experts!

We’ve had a few questions lately about the best method of bonding rubber to aluminum before overmolding. It seems this bonding combination poses a tough challenge. And in many cases, we’re finding that companies want to achieve better bond strength without using harsh solvents. So how can you achieve one without the use of the other? Plasma cleaning is the answer.

Plasma vacuum cleaning prepares metal substrates by removing all contaminants without the use of solvents, and with no damage to the components. Plasma is a one-step and solvent-free process to improve bonding silicone rubber to aluminum ― or virtually any other material combination. Because when you begin with a spotless component you can dramatically increase the success of overmolding. 

You can check out our video for additional information or submit a Surface Modification Design Sheet to submit your specs for a quote. Learn how surface modification can also help prepare polymer substrates for bonding.

Here’s a fishing tale about the one that didn’t get away! 

Our team worked with a high-end fishing manufacturer to design a whole new reel drag system. The drag is actually a slip-clutch assembly that allows the line to move freely under the pressure of a sudden hook or the pull of a large fish ― basically keeping the fish engaged while the line is hauled in. 

Why did we choose Rulon LR and Rulon J formulas for this unique clutch application? It all came down to matching the right compounds to the right surface materials.

The new clutch devices incorporate carbon composite bushings for the drag pin and drag washers. With this combination of Rulon materials, the reel now produces a very efficient and smooth transition during drag adjustments. Rulon has helped to increase the drag response time, given longer wear life and provided a competitive value.

Since this initial reel development, our Surface Modification team has also worked with other high-end manufacturers to bond washers to the reel’s metal substrates. 

An added bonus is that Rulon is a self-lubricating material that eliminates the need for manual greasing for the lifetime of the product. 

Ever wonder if the Rulon material that you have purchased is the “reel” deal? Get your free copy of our technical paper, How to Recognize Genune and Avoid Counterfeit! Or just Ask an Expert!