20. March 2015   9:48 am
Dr. K. L. Mittal, Dr. Robert H. Lacombe

Dr. K. L. Mittal, Dr. Robert H. Lacombe

The previous issue of the “SURFACES: THE INVISIBLE UNIVERSE” blog focused on the topic of polymer surface modification. In this issue we continue on this topic and would again like to remind the reader of the upcoming Tenth International Symposium on Polymer Surface Modification: Relevance to Adhesion, to be held at the University of Maine, Orono, June 22-24 (2015). All readers are cordially invited to join the symposium either to present a paper on their current work in this field or to simply attend and greatly expand their awareness of current developments. Further details are available on the conference web site at: www.mstconf.com/surfmod10.htm

 

PLASMA CHEMISTRY OF POLYMER SURFACES

We continue our discussion on the topic of polymer surface modification via a book on this most important subject:

The Plasma Chemistry of Polymer Surfaces: Advanced Techniques for Surface Design, by Jörg Friedrich (WILEY-CVH Verlag GmbH& Co. KgaA, 2012)

The author began his studies in Macromolecular Chemistry at the German Academy of Sciences in Berlin and has been active in this field ever since and is now professor at the Technical University of Berlin. He is best know to us through his past participation in previous gatherings of the above mentioned Polymer Surface Modification symposium series going back to 1993.

In his introduction Prof. Friedrich points out the apparently incredible fact that more than 99% of all visible matter is in the plasma state. A moments reflection, however, easily confirms this statement since the Sun above, which of itself accounts for more than 99% of all matter in the solar system, is in fact an exceedingly dense and hot ball of plasma. Here on earth the plasma state is rarely observed outside of special devices and consists mainly of low and atmospheric pressure plasmas which are a source of moderate quantities of energy mainly transferred through the kinetic energy of free electrons. Such plasmas have sufficient energy to produce reactive species and photons which are able to initiate all types of polymerizations or activate the surface of normally inactive polymers. Thus plasmas offer the opportunity to promote chemical reactions at surfaces which would otherwise be difficult to achieve. However, the very active nature of plasma systems also present a problem in that the broadly distributed energies in the plasma can also initiate a wide range of unwanted reactions including polymer chain scission and cross linking. The problem now becomes how does one tame the plasma into performing only the chemical reactions one desires by eliminating unwanted and destructive processes. This is the topic to which we will give more attention to shortly but first a quick look at the contents of the volume.

The volume is divided into 12 separate chapters as follows:

  1. Introduction
  2. Interaction Between Plasma and Polymers
  3. Plasma
  4. Chemistry and Energetics in Classic and Plasma Processes
  5. Kinetics of Polymer Surface Modification
  6. Bulk, Ablative and Side Reactions
  7. Metallization of Plasma-Modified Polymers
  8. Accelerated Plasma-Aging of Polymers
  9. Polymer Surface Modifications with Monosort Functional Groups
  10. Atmospheric-Pressure Plasmas
  11. Plasma Polymerization
  12. Pulsed-Plasma Polymerization

Given the above list I think it can be fairly said that the volume covers the entire range of surface chemistries associated with plasma processes and far more topics than can be adequately addressed in this review. Thus the remainder of this column will focus on the above outlined problem of controlling the surface chemistry by taming normally indiscreet plasma reactions. This problem is discussed in chapters 9 and 12 of Prof. Friedrich’s book.

Chapter 9 attacks the problem of controlling an otherwise unruly surface chemistry initiated by aggressive plasma reactions through the use of “Monosort Functional” groups. For the benefit of the uninitiated we give a short tutorial on the concept of functional group in organic chemistry. The term functional group arises from classic organic chemistry and typically refers to chemical species which engage in well known chemical reactions. The classic example refers to chemical species attached to hydrocarbon chains. As is well known the hydrocarbons form a series of molecules composed solely of carbon and hydrogen. The simplest which is methane or natural gas which is simply one carbon atom with 4 hydrogens attached in a tetrahedral geometry and commonly symbolized as CH4. The chemistry of carbon allows it to form strings of indefinite length and in the hydrocarbon series each carbon is attached to two other carbons and two hydrogens except for the terminal carbons which attach to one other carbon and 3 hydrogens. Thus moving up the series we get to the chain with 8 carbons called octane which is the basic component of the gasoline which powers nearly all motor vehicles. Octane is a string of 8 carbons with 6 in the interior and two on the ends of the chain. The interior carbons carry two hydrogens and the two end carbons carry 3 hydrogens each giving a total of 18 hydrogens. Octane is thus designated as C8H18. Moving on to indefinitely large chain lengths we arrive at polyethylene which is a common thermo-plastic material used in fabricating all varieties of plastic containers such as tupper ware® , plastic sheeting and wire insulation. Outside of being quite flammable the low molecular weight hydrocarbons have a rather boring chemistry in that they react only sluggishly with other molecules. However, if so called functional groups are introduced the chemistry becomes much more interesting. Take the case of ethane C2H6 the second molecule in the series which is a gas similar to methane only roughly twice as heavy. If we replace one of the hydrogens with what is called the hydroxyl functional group designated as -O-H which is essentially a fragment of a water molecule, ie H-O-H with one H lopped off, we get the molecule C2OH6 which now has dramatically different properties. Ethane the non water soluble gas becomes ethanol a highly water soluble liquid also known as grain alcohol and much better known as the active ingredient in all intoxicating beverages. Thus through the use of functional groups chemists can work nearly miraculous changes in the properties of common materials and Prof. Friedrich’s monosort functionalization is a process for using plasmas to perform this bit of magic on polymer surfaces by attaching the appropriate functional groups. The process can be rather tricky, however, and requires understanding of the physical processes involved at the atomic and molecular level.

The following example illustrates the nature of the problem and how successful functionalization can be carried out using plasma technology.

Figure (1a) illustrates the basic problem with most common plasma surface treatments. The exceedingly high energy associated with the ionization of oxygen coupled with the equally high energies associated with the tail of the electron energy distribution give rise to a panoply of functional groups plus free radicals that can give rise to degradation and crosslinking in the underlying polymer substrate. Thus it would be difficult to control the chemical behavior of the nonspecific functionalized surface shown in Fig.(1a) with regard to further chemical treatment such as the grafting on of a desired molecule. In essence the wide range of chemically reactive entities make it very difficult to control any further chemical treatment of the surface due to the presence of a wide range of reactive species with widely different chemical behaviors.

Prof. Friedrich points out that unfortunately most plasma gasses behave as shown in Fig.(1a) but somewhat surprisingly use of Bromine (symbol Br) is different due to a special set of circumstances related to the thermodynamic behavior of this molecule, which are too technical to go into in this discussion. It turns out that bromine plasmas can be controlled to give a uniform functionalization of the polymer surface as shown in Fig.(1b). The now uniformly functionalized surface can be subjected to further chemical treatment such as grafting of specific molecules to give a desired well controlled surface chemistry.

In a similar vein, in chapter 12 Prof. Friedrich approaches the problem of plasma polymerization through the use of pulsed as opposed to continuous plasma methods. The problem is much the same as with the surface functionalization problem discussed above. Continuous plasmas involve a steady flux of energy which gives rise to unwanted reactions whereas by turning the energy field on and off in a carefully controlled manner limits the amount of excess energy dumped into the system and thus also the unwanted side reactions.

As this blog is already getting too long we leave it to the interested reader to explore the details by consulting Prof. Friedrich’s volume. As usual the author welcomes any further comments or inquiries concerning this topic and may be readily contacted at the coordinates below.

 

Dr. Robert H. Lacombe, Chairman

Materials Science and Technology CONFERENCES

3 Hammer Drive, Hopewell Junction, NY 12533-6124

Tel. 845-897-1654, FAX  212-656-1016; E-mail: rhlacombe@compuserve.com

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Category: LIFE SCIENCES
17. March 2015   12:01 am
Khoren Sahagian

Khoren Sahagian

We were pleased to learn that a team of researchers from the University of California, Berkeley will be presenting their findings related to a method of surface modification introduced by Plasmatreat North America. The work will be shared at the upcoming annual meeting for the American Association for Thoracic Surgery.

Researchers at UC Berkeley worked with the team at Plasmatreat N.A. to identify an effective method for heparin immobilization on electrospun polycarbonate-urethane vascular grafts.  Heparin incorporation provides implantable medical devices with antithrombotic characteristics.

The team explored three surface modification techniques:

  • aminolysis with 1-Ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC) chemistry as a chemical immobilization
  • polydopamine coating as a passive adsorption
  • plasma treatment paired with end-point immobilization to ultimately conjugate heparin on the graft surface.

 

The most effective modification was determined with respect to the heparin density as well as the antithrombogenic activity of the immobilized heparin. Then, the team proceeded with these optimized PCU grafts immobilized with heparin for short-term in vivo studies.

After 4 weeks, plasma-control grafts exhibited approximately 29% (2 of 7) patency, compared to 86% (6 of 7) patency of plasma-heparin grafts. More importantly, the team observed a more complete endothelialization of the luminal surface with a more aligned, well-organized monolayer of endothelial cells.

The team concluded, in vitro, that the combination of plasma treatment and end-point immobilization of heparin drastically improved the performance of the vascular grafts with respect to patency as well as early stages of endothelialization.

These findings are tremendously exciting because they signal a new era for implantable medical devices. In the past, a goal was to evade biological responses by selecting inert materials that delay host rejection.

Now, however, material modification are allowing researchers to immobilize biomolecules or cytokine, which in turn allows the surface of the device to regulate cellular behavior and to engineer surface response.

The team at Plasmatreat N.A. wants to thank our collaborators at University of California, Berkeley for their innovative utilization of plasma surface modification. Surface chemistry and topography play integral roles in biological development and remodeling. Gas plasma technologies are an effective tool for customized surface engineering.

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Mikki Larner

Mikki Larner
Vice President Sales & Marketing
Belmont, CA

Editorial March 2015

I just celebrated my 15th year in the plasma surface modification business. And I have gathered 15 years of misconceptions and have, successfully I think, been able to educate and raise the awareness of the technology’s flexibility for designing working surfaces and dispel many of these.

The most common are:

  • It doesn’t last
  • All equipment is the same
  • All plasmas are the same
  • I tried argon and oxygen and it didn’t work, thus plasma doesn’t work
  • It produces ozone
  • It just oxidizes the surface
  • It is expensive

 

With my colleagues, I have published papers (with a book chapter pending!) and presented at numerous conferences, exhibitions and companies. Plus provided workshops on the technology to a variety of audiences. I love doing this because I’m always dispelling these misconceptions and educating about the diverse field of plasma. One of our advisors has coined the term “plasmersion.” It is a fun way to think about the process (and the work as a noun): the part is typically immersed in the plasma (in the case of the 3-d vacuum plasma treatment) and with Openair the surface to be treated is immersed in the plasma. It also could be used as a verb, and I’m plasmersing folks in our technology.

With that said, I’d like to remind you of the services that I offer.

In addition to Plasma Technology Systems’ long history of providing professional commercial solutions (30 years and counting) and our exceptional customer service, we offer what we believe to be the most diverse private-sector atmospheric and low pressure plasma equipment suite and surface chemistry offerings in the world.

We have a global network of partners and subsidiaries in all key industrial markets that enables us to provide our customers with all-in-one solutions (both bespoke and off-the-rack).

Depending on your specific relationship with us, you may not know that we offer all of the following:

  1. Research and Process Development:  We offer a highly creative yet low-risk environment for the evaluation and development of novel gas plasma processes, for small start-ups to Fortune 500 companies. Customers can bring us their own ideas or pull from our extensive (and ever-expanding) process and chemistry library.  We can advise you on specific plasma issues, develop plasma processes to address your specific needs, and assist in the development of a full-scale plasma system tailored to your specific requirements.
  2. Contract Manufacturing Services.  We have a fully equipped ISO: 9001 contract manufacturing division (4th State, Inc.) in Belmont, California (just north of Silicon Valley), where we modify materials on a contract basis. This is an ideal solution for companies that are not ready for the technology transfer. These contract manufacturing services enable a seamless translation of process to production with no capital expense, for your smallest and largest products—from powder to 1.5 meter-wide rolled goods. This is another area where we offer risk reduction. You can test your product in the market first, gain acceptance and confirmation of volumes, and then lease or purchase the equipment.
  3. Equipment Solutions.  From small batch to large batch to fully integrated work cells, our team delivers standard systems and custom platforms for low-pressure and atmospheric plasma technology. Depending on the technology, you have the option to buy the equipment outright or lease it from us with warranty support for the term of the lease. Our equipment solutions also include installation, training support and calibration services. And we maintain a full supply of spare parts in two facilities to support our North American customer base.

If you take nothing else away from this message, remember this: We offer a whole lot more than you probably think we do. So if there’s ever anything we might be able to help you out with, give us a call—you may be pleasantly surprised to find out that it’s the only call you need to make.

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5. March 2015   2:00 pm
Andy Stecher

Andy Stecher
Elgin, IL

NPE2015

If you, like me, are old enough to recall the classic 1967 film The Graduate, you know it features many memorable scenes.

One of my favorites takes place when newly minted college graduate Benjamin Braddock (Dustin Hoffman) is drifting around his parents’ pool, trying to figure out what to do with his life. One of his father’s friends, identified only as Mr. McGuire, stops by and offers a one-word piece of unsolicited advice: “Plastics.”

While the scene is played for laughs, looking back now from a distance of nearly 50 years—unbelievable, isn’t it?—Mr. McGuire was clearly onto something. New technologies are revolutionizing the industry at an incredible pace, which is why I’m very much looking forward to Plasmatreat North America’s participation in the upcoming NPE2015 International Plastics Showcase in Orlando later this month.

As you may know, NPE takes place only once every three years, and it’s a massive, exciting event. If you’re planning to attend, please do stop by our booth (W8078) and say hello.

We will be treating parts on-site in our enclosure and verifying the effects with the handheld Brighton Surface Analyst tool. Additionally, we’ll have a KUKA Agilus robot on display demonstrating some of our advanced automated surface treatment solutions.

Finally, I will be presenting a paper at ANTEC, the annual technical conference that will run concurrently with NPE this year. The topic is “Managing Global Challenges with Micro Solutions: The Role of Plasma Surface Treatment in the Future of Plastics.”

I’ll cover seven global trends in plastic part manufacturing, each of which represents new business opportunities—and technical challenges. Plasma surface treatment poses an elegant, environmentally friendly, cost-effective means for meeting these new challenges, so I hope you will consider stopping by to hear all the details!

As always, if you have any questions about our participation in NPE2015 or anything else, please do let us know and we’ll be delighted to chat further. Hope to see you in Orlando in a few weeks, and best wishes for safe and smooth travels to our fellow exhibitors and attendees.

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