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1 min read

Defined: Hydrophilic, Hydrophobic, Oleophilic, Oleophobic & Hygroscopic

By Frank Hild on February 27, 2019

Hydrophilic, Hydrophobic, Oleophilic, Oleophobic & Hygroscopic

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.

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Topics: Surface Modification Enhanced Materials
2 min read

How do Surface Treatments Work? Part 1: Corona Treatment

By Dave Biering on December 6, 2016

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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

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Topics: Surface Modification
1 min read

3 Key Benefits of Surface Modification

By Dave Biering on December 9, 2014

TriStar Plastics Corp. - 3 Key Benefits of Surface ModificationReading 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!

Topics: Surface Modification Plasma Treatment
1 min read

Tech Tip: How do I measure the surface tension of plastics?

By Dave Biering on September 30, 2014

Measuring Surface AngleMeasuring 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:

Surface Energy and Contact Angles 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!

Topics: Surface Modification
1 min read

Tips to Bond Silicone Rubber to Aluminum

By Dave Biering on September 23, 2014

Plasma cleaning of metal parts dramatically increases the success of overmolding.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.

Topics: Surface Modification Bonding Plasma Treatment Rubber
1 min read

Rulon Reels In Custom Fishing Components

By Dave Biering on August 28, 2014

Rulon Reels In Custom Fishing ComponentsHere’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!

Topics: Rulon J Surface Modification Rulon LR
1 min read

Preparing Fluoropolymers for Bonding With Plasma Treatment

By Kevin Smith on March 19, 2013

PTFE MoleculeWe are often asked about which method is best for preparing fluoropolymers for a bonding applicationThe most critical step is bonding is to ensure that you begin with a clean surface.

Fluoropolymers are a group of polymers in which all, or most, of the hydrogen has been replaced with fluorine. They have a wide range of mechanical, frictional, chemical, and electrical properties which make them ideal for a many different applications. However, these properties result in such low surface energy levels they are difficult to bond without surface pretreatment.

Sodium-etch solutions are one common surface treatment used for bonding, but they have significant disadvantages.  The wet chemicals are expensive and dangerous, do not coat uniformly, and are very difficult to dispose of.   A better method of preparing polymers for bonding is by plasma treatment

The TriStar team has had good results with surface treatment of fluoropolymers such as FEP,PFA, Tefzel®, and PTFE (Teflon®) with gas plasma.  If an appropriate process is used, the surface of the fluoropolymer is chemically modified and becomes water-wettable, printable and bondable with structural adhesives. The plasma treatment is uniform, dry (no wet chemistries), efficient, and safe. And the process is earth-friendly with no disposal issues.

Wondering if plasma is the right treatment for your bonding challenge?  Reach out to our team to learn more

Topics: Surface Modification
1 min read

Plasma Surface Modification – How does the process work?

By Kevin Smith on January 22, 2013

I often receive calls asking to explain, “How does a low-pressure plasma tool actually work?”  I thought I’d share a diagram that we often use to explain the process.  The plasma process is widely used to critically clean and functionalize the surface of components.   After a plasma treatment, components are able to better accept paints, adhesives, inks and coatings.

Simply put, plasma treatment is the grafting of chemical functional groups to the polymer backbone by first removing an elemental component, then replacing it with a functional element.

Plasma Treatment Process

Plasma processing is done in a controlled environment at sub-atmospheric pressure, specifically, a partial pressure (vacuum) with only a particular process gas (or groups of gases) present. The process gas is excited with a high frequency field causing the gas molecules to ionize. This increases the energetic free radicals which react with the molecules on the surface of the material being treated. This reaction includes physical bombardment, oxidation, grafting, cross-linking and even polymerization of the surface molecules.

This is just a quick overview of the process.  Reach out to our Surface Modification Experts for additional information to learn how plasma modification can benefit your manufacturing processes.

Topics: Surface Modification
1 min read

Increasing adhesion on hard-to-bond materials like Delrin

By Kevin Smith on December 4, 2012

Blog 20121204Question: How do I bond Delrin to other materials?

Delrin (also known as Acetal, Polyocymethylene (POM), polyacetal, and polyformaldehyde) is an engineered polymer that is commonly used in the manufacturing of precision parts.  It is a fairly rigid plastic that exhibits low friction and maintains good dimensional stability and good abrasion resistance.  It also has low moisture absorption, good heat resistance, and (like most plastics) is a good dielectric.


Unfortunately, like many engineered and high performance polymers, it can be very difficult to bond, especially with conventional adhesives.  However, Delrin can be made easily bondable with any number of simple pretreatments such as chemical etching, flame treatment, or surface roughening (abrasion).  Of these treatments, the most effective is a plasma treatment to clean and functionalize the material.  Although a corona treatment can be effective, it does not offer the same level of uniformity or treatment lifetime that can be achieved with a low-pressure (vacuum) plasma treatment.  In the case of Delrin, and many other engineered or high-performance polymers, an oxygen plasma treatment may be all that is required to make the material bondable with conventional epoxies, urethanes, or cyanoacrylate adhesives.

Is Delrin right for your next application?  Consult our Experts to find out more!

Topics: Material Selection Surface Modification
1 min read

5 Common Gases to Render Polymer Surfaces Hydrophilic

By Kevin Smith on October 23, 2012

Functional groups via plasma processing

Plasma TreatmentsHere is a quick review of five gases that create polar entities on a polymer surface to render it hydrophilic (or wettable):

  1. Oxygen - generally the most effective process gas for increasing surface energy – it creates carbonyl, carboxyl, ester, ether, hydroxyl, and hydroperoxyl functional groups, among others.
  2. Nitrogen - create amino groups, although the specific composition and density differ
  3. Ammonia - like nitrogen, ammonia creates amino groups with varying compositions and density
  4. Argon - the free radicals produced by argon, while promoting crosslinking, are also long-lived; thus, when a treated part is removed from the plasma chamber and exposed to the atmosphere, oxygen-containing groups (predominantly hydroperoxyl groups, it is believed) form.  These may subsequently react with the adhesive to create a covalent bond at the interface.  
  5. Air - is a very complex process gas, and produces all of the functional groups produced by the other four gases.  

The best technique to analyze the chemistry of the functional groups on a polymer surface is an electron spectroscopy; our Surface Modification team is also available to help.

Topics: Surface Modification
1 min read

Plasma Modification – The Basics: Oxidizing species

By Kevin Smith on July 17, 2012

Our Surface Modification team is often asked about the benefits of low-pressure plasma treatments.  Plasma offers many advantages to industries ranging from medical and biotech to aerospace and automotive.   For the next few weeks, I’ll touch on some of the basics that are helpful to know when considering plasma treatment for your application. 

Oxidizing species such as air, oxygen, water vapor, or nitrous oxide are often used as processing gases in low-pressure (vacuum) plasma systems to remove organic contaminates and to leave functional oxygen-containing groups on the surface of the device and/or material being treated.  These groups greatly enhance wetting and improve the bond-strength of adhesives, inks or paints, tapes, encapsulation/potting resin, and coatings.

Reducing gas species such as hydrogen or methane (often mixed with argon, helium, or nitrogen) may be used to remove organic contamination from substrates that may be sensitive to oxidation.  This chemistry may also be used to partially substitute hydrogen atoms for fluorine or oxygen on the surface of polymer substrates.  The noble gas species, such as argon or helium, are chemically inert so they do not combine or become part of the surface chemistry.  Instead, they transport energy to break chemical bonds in polymer chains.  Broken polymer chains result in dangling bonds which recombine with other reactive sites, resulting in significant molecular restructuring and/or crosslinking.  The creation of dangling bonds allows for chemical grafting reactions to occur.

Have questions on plasma processing?  Consult our Experts to learn more.  

Topics: Surface Modification
1 min read

Q&A: Treating Acrylic with Plasma

By Kevin Smith on February 28, 2012

Question:

We are attempting to bond two machined pieces of acrylic together to form a microfluidic device. I know that direct plasma bonding of acrylic won't work, but that plasma treatment of the acrylic can lead to a much better seal/bond when using an adhesive (e.g., epoxy).

Can you recommend a good starting place for a plasma surface treatment of acrylic, such as gases, ballpark power value, time, etc.?

Answer:

It is true that acrylic bonding is easily achieved via solvent and/or heat welding, but if the material is be bonded by applying a conventional cyanoacrylate or epoxy, a quick pretreatment with vacuum plasma can – as you mentioned – significantly improve the strength of the bond.  In the case of treating acrylic, the preferred treatment gas is oxygen. The power required is minimal as is the processing “plasma on” time.  It can be easy to “over process” some materials; this is true with acrylic.  The amount of time that the devices are processed in the chamber can depend on the type of system used, the amount of gas flow, and the load size.  For a full load of devices in a medium-sized chamber, a treatment time of 5 minutes should be fine; however, you should test random samples with a goniometer (or Dyne pens) to make sure that the treatment is uniform and effective.

Slight adjustments to power and time will help you optimize the process for your parts and volumes.

TriStar can assist in the plasma recipe development process; just contact us to discuss your application and production requirements.  As a side note, since you will be using pure oxygen as a process gas, it is important (from a safety standpoint) that your plasma system is equipped with a vacuum pump that is either a dry (scroll) or is lubricated with PFPE (Fomblin or Krytox) oil.  Vacuum pumps used for plasma systems should not be lubricated with conventional hydrocarbon oils if oxygen is used as a processing gas.

Do you have a question about bonding your application?  Our surface modification team can help find a solution!

Topics: Surface Modification Q&A