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ramé-hart Newsletter

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May 2022

Plasma Treatment and Contact Angle
Plasma treatment is often used in manufacturing environments prior to bonding, painting, coating, and sealing in order to prepare the surface for optimal adhesion. The process actually performs two critical tasks: cleaning and surface activation.

Solid, liquid, and gas are three states of matter that everyone is familiar with. Plasma is the fourth state of matter and, although less understood, it is the most abundant state of matter in the universe.

Oxygen, compressed air, and argon are gases that are commonly used to artificially generate plasma by heating or applying an electromagnetic field. Organic contaminants on inorganic surfaces, for example, will oxidize and can be easily blown off when plasma treated. When the surface is organic, plasma will oxidize the surface and produce hydroxyls. The result is a cleaner and activated surface with much higher surface energy which is reflected by a decrease of the contact angle.

Manufacturing processes that involve bonding two disparate materials (such as a metal to a polymer) can benefit from plasma treatment. The first few layers of matter on the treated surfaces will become energized. These activated surfaces have much better adhesion and respond better to most bonding methods. The greater the time period between plasma treatment and bonding, however, the less effective the treatment is. That is, the surface activation wears off over time, it becomes less energized you could say.

Vacuum plasma treatment has been around for a long time and is a cost-effective way to activate the surfaces of polymer and other chemically inert materials prior to bonding and coating processes. Parts to be treated are placed in a vacuum chamber (years ago ramé-hart used to make a vacuum chamber) and connected to an electrical source, a vacuum is made, and then gas is introduced to the chamber. The electrical energy promotes a controlled plasma condition which excites the surface and activates the first few layers of molecules on the parts. The vacuum promotes uniform treatment even on parts of any complex shape.

Most plasma treatment can also be done at atmospheric pressure using common industrial gasses such as hydrogen, oxygen, and nitrogen. No chemicals are necessary making the process environmentally friendly. Arc discharge uses large DC currents at low voltage. Corona discharge relies on high-voltage electrodes which produce corona when an electrical discharge ionizes the the gas. Other methods include piezoelectric direct discharge and dielectric barrier discharge.

Untreated textured polymer surface with water contact angle of 84.9° measured with DROPimage Advanced on ramé-hart Model 250

Same textured polymer surface after 5 minutes of plasma treatment with water contact angle of 50.3° also measured on ramé-hart Model 250

Many variables can control the effectiveness of any plasma treatment - the gasses used, the chamber pressure, the duration of treatment, and so on. Thus, there is a need for measuring the effectiveness of a particular treatment and the parameters used. This is often done by measuring the contact angle of treated parts. Many manufacturing processes require the water contact angle of a plasma treated part to fall within a specified range. If the contact angle falls above this expected threshold, it must be rejected or retreated. A more comprehensive approach is to measure the surface energy using two or more liquids.

Contact angle is a primary method for characterizing surfaces that have been plasma treated. Multiple liquids can be used to determine surface energy and roll-off angle is auxiliary metric that is often used.

Product Comparison: Models 210 and 250
ramé-hart Models 210 and 250 are two of our best selling instruments. While they share the same hardware, there are some significant differences between these two models.

First, what's in common? Both ship with our German-made U4 Series SuperSpeed digital camera which runs at speeds up to 540 fps at full resolution. Both include our fiber optic illuminator and 16-inch optical bench. Both include our standard 3-axis stage with rack-and pinion movements in two directions and precision lead screw movement in the third direction. The specimen stage can be leveled up to 15° in any direction. Both are complete turn-key instruments ready to plug-and-play right out of the box.

So, what's different? The software. Model 210 ships with our DROPimage Pro package while Model 250 ships with our more powerful DROPimage Advanced package. The Pro software can measure contact angle, surface energy, surface tension, and interfacial tension along with support for our Automated Dispensing System. DROPimage Advanced adds a methods-based experiment design tool which is greatly automated for doing any type of dynamic or time-dependant study. In addition, DROPimage Advanced adds support for our Automated Tilting Base, Oscillator, and logging for a variety of temperature-controlled chambers and our hot plate.

Some of our customers start with Model 210 and then later upgrade the software as needed. That's one of the compelling competitive advantages of ramé-hart instruments. They are incredibly modular and with over two dozen available accessories and upgrades, your next instrument can be customized for your specific application and requirements.

Please contact us if you would like a quotation for a Model 210, 250, or for any of our instrument products.


Carl Clegg
Director of Sales
Phone 973-448-0305
Contact us


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