This issue of the SURFACE SCIENCE CORNER has the dual purpose of presenting a book review on a recently published volume while simultaneously having a look at the amazingly ubiquitous world of adhesives technology. The volume in question is:

ADHESION SCIENCE: PRINCIPLES AND PRACTICE
Steven Abbott, (DEStech Publications, Inc., 2015)

Though the title would give the impression of dealing with the broad topic of adhesion science the volume is in fact closely focused on the topic of adhesives technology. This is not only a good thing but a necessary one also since dealing with the general topic of adhesion would require an encyclopedia series as opposed to a relatively compact volume.

What struck me most upon reading the volume was the amazing ubiquity of adhesive applications which we encounter in our everyday lives and the broad range of thermal-mechanical requirements that these applications require. Have a look around your local supermarket if you are not convinced about pervasiveness of adhesives in our day to day lives. Every glass jar has an adhesive attaching the label, every cardboard box is held together with an adhesive, all the bubble pack packages containing everything from paperclips to cutlery are sealed with an adhesive. Even going over to the fresh produce tables with fruits and vegetables laid out completely bare of any packaging materials whatever one finds sneaky little labels adhered to nearly everything with the items PLU code printed on it. It is not an exaggeration to say that the entire contents of the store are held together with an adhesive of one kind or another.

Looking around my office I see the ever present Postit® notes plastered on nearly every vertical and horizontal surface as well as interleaving the pages of most of the volumes on my bookshelf. Thinking about it one realizes the that the Postit note is a rather remarkable technology in that the note must adhere quickly to a broad range of surfaces without any surface pretreatment whatever and must also be cleanly removable without damaging the surface in question. Thus the Postit note puts a stake in the ground at one end of the adhesive performance spectrum which requires rapid easily reversed adhesion to a wide range of surfaces without regard to any sort of surface treatment other than perhaps blowing off some dust.

Going to the other end of the spectrum we find the adhesives which are used to glue together high performance aircraft. The requirements for this application are totally the opposite from those of the Postit note. All surfaces are carefully cleaned and treated with special primers. Maximal joint strength is required over a wide range of temperature and environment conditions giving a bond that needs to be totally irreversible.

Sitting between the extremes of the Postit note and aircraft glue is a vast range of intermediate applications ranging from gluing together the common cereal box to gluing the windshield onto your automobile. Consider the cereal box. Here fairly strong adhesion is required since the container cannot fall apart too easily but the adhesion cannot be too strong since the consumer has to be able to open the package without excessive force. On top of these requirements the adhesive material must be inexpensive and easily applied without surface preparation since the manufacturing volumes involved are enormous.

The case of adhering to windshield glass presents an entirely different set of requirements. In case you are not aware, many windshields in the newer car models are glued to the frame. Not only that but you also find that the rearview mirror is also glued to the glass. I can attest directly to this fact since the rearview mirror on my car fell off recently and needed to be reattached. The requirements here are dramatically opposite to the cereal box. First the bond must be permanent. Second the bond must withstand a wide range of temperature cycling from say 10 degrees F below zero in Winter to over 100 F in summer for a vehicle parked in the sun. Third the adhesive must withstand extensive exposure to ultra violet radiation from the sun. Given these requirements I thought it best to go to the auto parts store and purchase an adhesive specially formulated for attaching rearview mirrors.

The procedure for attaching my mirror was more like using aircraft glue than bonding a cereal box. First the glass and the attachment button were cleaned with acetone to remove all residual adhesive. Second a primer layer had to be applied to the glass and allowed to set for a specific time. Finally I was directed to apply only a thin layer of the adhesive to the attachment button which was then pressed in place for a full minute to get initial attachment. An hour or so or curing time was needed to achieve full strength before the mirror could be attached to the button.

Getting back to the volume under review it is clear upon cursory reading that the author has spent considerable time in the adhesives formulation business. The table of contents gives an indication of the flavor of the topics covered:
1. Some basics: Reviews the rudiments of adhesion measurement and adhesion failure mechanisms.
2. The Myths around Surface Energy and Roughness: An entertainingly provocative review of the concepts of surface energy and surface roughness as applied to adhesives technology.
3. Intermingling and Entanglement: Brings into focus the critically important role of the adhesive bulk properties on its adhesion performance. In particular the crucial role of polymer molecular weight and chain segment mobility are discussed in regard to achieving high adhesion strength.
4. Time is the Same as Temperature: Discusses the critical importance of the concept of Time Temperature Superposition in determining the thermal-mechanical properties of all adhesive formulations.
5. Strong Adhesion with a Weak Interface: Review of the important topic of pressure sensitive adhesives.
6. Formulating for Compatibility: Discusses the importance of polymer solution thermodynamics in the development of adhesive formulations.
7. Measuring Adhesion: Perils and Pitfalls: Gives a review of the most common adhesion measurement methods used for evaluating adhesive formulations.
8. Putting Things into Practice: Gives a comprehensive summary of how all the above topics can work together in the “scientific” design of adhesive formulations.

Topics 2 and 3 above are of most interest to the subject of applying plasma technology to improving adhesion to polymer substrates. The essential point of chapter 2 is that the role of surface energy in promoting adhesion to crystalline polymers is basically misunderstood. It is well known that it is difficult to adhere anything to crystalline polymers such as poly(ethylene) PE, poly(ethylene-terepthalate) PET and poly(propylene) PP. It is also well known that plasma treatment greatly improves the adhesibility of all of these materials. The question is what is going on?

The standard answer is that plasma treatment is improving the surface energy of these materials thus allowing greater wetting as well as stronger interactions at the interface via the creation of functional groups. The author argues persuasively that this is unlikely to be the case. Looking at polyethylene for example, standard analysis reveals the surface energy to be roughly 32 mJ/m2 (milli joules per square meter). Plasma treatment will typically raise the surface energy to something like 42 mJ/m2 or about a 30% increase. This figure, however, does not square with the observed increase in peel test adhesion which can be in the range of 10 to 100 J/m2 (joules per square meter) or several orders of magnitude larger than the increase in surface energy.

Further suspicion is cast on the surface energy argument by the comparison of poly(ethylene terephthalate)PET to poly(vinyl chloride) PVC. The surface energies of these two polymers are close to 43 mJ/m2 but it is well known that it is difficult to adhere to PET compared to PVC. Again we have wonder what is going on?

A clue begins to emerge in the case of PE. This polymer comes in two basic forms one of low density LDPE and one of high density HDPE. The high density form is essentially one long completely linear chain of CH units and therefore tends to be highly crystalline. The low density form, however, is composed of linear strings of CH units broken up at intervals by short side chains of CH units terminating in a CH3 group. The many side chains of the LDPE prevent it from attaining the same level of crystallinity as its HDPE cousin thus resulting in lower density. It is also known that it is easier to adhere to low density PE than the high density form. If we combine this with the fact that the poorly adhesionable PET is a highly crystalline polymer and the easily adhesionable PVC is totally amorphous then we have to suspect that it is the level of crystallinity that is key in determining adhesability.

It is at this point that the mechanisms of chain intermingling and chain entanglement enter the picture. In essence amorphous polymers have a high degree of chain segment mobility which allows them to interpenetrate and form entanglements which give rise to high levels of energy dissipation when trying to pull them apart. Think of trying to pull part two lengths of string that have been randomly jumbled together. It is these strongly dissipative effects that give rise to the apparent strong adhesion observed in peeling apart these intermingled and entangled layers.

Now the question becomes what is the role of plasma treatment in improving the adhesionability of crystalline polymers? Aside from improving the wettability of the treated surface the most obvious mechanism is the disruption of the surface crystalline layers of the polymer. Plasma treatment always involves the making and breaking of chemical bonds and in the case of crystalline polymers we postulate that the plasma field breaks up a significant amount of surface crystallinity creating an amorphous layer with highly mobile chain segments capable of intermingling and entangling with applied surface layers. The existing level of surface energy must be sufficient to allow for a reasonable amount of wetting, but beyond that it does not add significantly to the overall peel removal energy which is dominated by the dissipative effects of chain interpenetration and entanglement.

Prof. Abbott points out that the adhesion mechanisms described above have a strong influence on how the typical adhesive is formulated. The redoubtable formulator is generally faced with the prospect of joining two poorly or wholly uncharacterized surfaces and his customer wants an inexpensive and easily applied glue that will hold these surfaces together with just the right amount of strength and durability called for. He has to assume that the surface energies will be in a reasonable range to give sufficient wetting without the need to perform any sort of involved surface analysis or surface preparation aside from a perfunctory cleaning. Plasma treatment will be a very handy tool when dealing with difficult surfaces such as the crystalline polymers but it must be remembered that all that is required is to sufficiently break up the crystallinity of just the top most surface layer in order to get chain interpenetration. Over treatment must be avoided so that one does not create a layer low molecular weight rubble that could act as a weak boundary layer and thus give even poorer adhesion than the original untreated surface.

As luck would have it not only did my rearview mirror fall off but also the soles of my cycling shoes delaminated. Thus I got to try out a totally different kind of adhesive from what I used to attach my mirror. Commonly called shoe goo it is apparently some kind of silicone polymer formulation. No surface preparation is required other than blowing out any loosely adhered debris. Contrary to the rearview mirror formulation there is no primer layer required and the glue is applied in a fairly thick layer and spread out as evenly as possible with a stick to give good coverage and penetration into all the nooks and crannies of the mating surfaces. After application of the glue I pressed together the mating surfaces under the weight of an inverted 10 pound sledge hammer in order to make maximal contact and then allowed everything to set and cure over a period of a day or two.

Thus the world of adhesives turns out not only to be very commonplace in our day to day lives but also rather subtle, deceptive and non-intuitive in terms of the science and technology required to create truly effective and useful formulations. The requirements from one application to another can be diametrically opposite and the formulator has but a limited number of theoretical tools available which must be carefully handled. The reader interested in further exploring this most engaging topic is encourage to refer to Prof. Abbott’s fine volume.

For my part I can confirm that both my rearview mirror and cycling shoes remain completely intact. So despite the subtle and intricate nature of adhesive technology good adhesives are available for nearly all practical purposes and Prof. Abbot’s volume is a most instructive guide for anyone faced with the problem of developing a working adhesive.

The author is happy to entertain any questions or comments concerning this topic and may be 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; 845-592-1963
FAX 212-656-1016
E-mail: rhlacombe@compuserve.com

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The last two issues of the SURFACE SCIENCE CORNER BLOG dealt with polymer surface modification through plasma processing. One of the main issues dealt with the problem of controlling the resulting surface properties created by the highly aggressive nature of the plasma environment. The large number of chemically active species in the plasma can give rise to unwanted surface chemistries unless special steps are taken to avoid this problem. The use of monosort functionalization and pulsed plasmas as discussed by Prof. Jeorge Friedrich in the previous issue of this blog are two possible ways of approaching this problem. However, the question still remains as to what changes in the surface were actually made after processing? This question brings us to the topic of surface characterization and in particular the use of contact angle measurements to conveniently and rapidly assess the wettability characteristics of a given surface.

In this regard, those who would have an interest in following the latest developments in the overall field of contact angle measurements and wetting behavior will definitely want to mark their calendars for the upcoming symposium:

TENTH INTERNATIONAL SYMPOSIUM ON CONTACT ANGLE, WETTABILITY AND ADHESION; to be held at the Stevens Institute of Technology, Hoboken, New Jersey, July 13-15, 2016.

Researchers from universities, technical institutes and industrial labs the world over will be presenting some of their latest work on this rapidly expanding technology which is finding applications in a wide range of cutting edge innovations including: self cleaning surfaces, nano and micro fluidics, microbial antifouling coatings, superhydrophobic and superoleophobic surfaces and electrowetting to name just a few of the more active research areas. Interested readers can follow the development of this meeting at the following web site:

www.mstconf.com/Contact10.htm

By way of an introduction to the topic of contact angle behavior, the remainder of this note will present some highlights of work presented at a previous meeting in the contact angle series held at Laval University in 2008. The rudiments of the contact angle experiment were covered in the July 2014 issue of this blog. The following discussion will cover some of the more current topics that were covered at the 2008 meeting in Laval.

Superhydrophobic/hydrophilic Behavior

The topic of superhydrophobic/superhydrophilic behavior was under very active investigation by many research groups worldwide as illustrated by the 9 papers submitted to the symposium. Applications range from self cleaning surfaces to preventing ice buildup on power lines. A most interesting paper was presented by Dr. Picraux from the Los Alamos National Laboratory entitled “Design of Nanowire Surfaces with Photo-induced Superhydrophilic to Superhydrophobic Switching”. The authors claim that they have developed functionalized photochromic monolayers for which the wetting angle of liquids can be reversibly switched optically by more than 100 degrees between superhydrophilic and superhydrophobic states. One would imagine that there would be tremendous applications for this technology in the realm of hand held tablets which are so tremendously popular these days.

Behavior of Water and Ice

During the week of January 5-10, 1998 a severe ice storm ravaged Southeastern Canada. The total water equivalent of precipitation, comprising mostly freezing rain and ice pellets and a bit of snow, exceeded 85 mm in Ottawa, 73 mm in Kingston, 108 in Cornwall and 100 mm in Montreal.   Further details of this horrific storm have been covered in the MST CONFERENCES newsletter and may be accessed at (www.mstconf.com/Vol5No1-2008.pdf). The prolonged freezing rain brought down millions of trees, 120,000 km of power lines and telephone cables, 130 major transmission towers each worth $100,000 and about 30,000 wooden utility poles costing $3000 each. Consequences for the local population were predictably disastrous with about 900,000 households without power in Quebec; 100,000 in Ontario. It is of little surprise then that the surface interactions of freezing water and aluminum power cables is of considerable interest to the Canadian government and of little surprise also that contact angle measurements are playing a significant role in the effort to understand and control these interactions. Thus no fewer than 4 papers were dedicated to this problem.

Novel Applications

It seems that hardly a day goes by but some new application of the contact angle behavior of surfaces arises apparently from nowhere. In fact, Carl Clegg of the ramé-hart instrument company has listed 50 different uses of the contact angle method ranging from the authentication of rare coins to the improved biocompatibility of polymer-based medical devices. For details see:

(www.ramehart.com/newsletters/2010-12_news.htm).

Adding to this there was a most interesting paper by Dr. Daryl Williams entitled “The Surface Energy of Pharmaceutical Solids- Its Importance in Solids Processing” which now adds pharmaceutical processing to the already extensive list. Undoubtedly even more unsuspected applications will surface in the future.

Oil Recovery and Mining Applications

The world’s insatiable thirst for fossil fuel products has lead to the quest to recover oil from progressively less productive sources such as tar sands and heretofore depleted wells. A moments reflection makes it clear that surface interactions between the residual oil and the surrounding rock are what dominates the problem of separating the oil from the rock. Again contact angle measurements are one of the leading methods being used to understand this problem.

Contact Angle in Micro and Nano Technology

The contact angle method is making remarkable inroads into the field of micro and nano technology mainly through the advent of micro-fluidics and micro-patterning of surfaces to control their wetting behavior. In the past I was always amazed at the very significant interest of Mechanical Engineering departments in the contact angle method. Being of the old school I always associated mechanical engineering with roads, bridges, automobiles, aircraft … etc. A moments reflection, however, quickly reveals that fluid flow is also an important mechanical engineering problem and that this problem is beginning to shift toward the micro-fluidics problem of flow in very small channels a micron or less in diameter. At this scale gravity is all but irrelevant and it is surface forces, governed by van der Waals interactions, that dominate. Again the contact angle technique is one of the most useful tools in investigating this behavior. Added to this the extensive efforts now underway in patterning surfaces to control their wetting behavior is bringing the contact angle method to the forefront in the realm of micro and nano technology. The paper presented by Dr. Mikael Järn of the YKI, Institute for Surfaces entitled “Wettability Studies of Selectively Functionalized Nanopatterned Surfaces” is a prime example of this new and exciting development in surface science.

Applications to Wood Science and Technology

Wood and wood products have been a mainstay of mankind since even before the dawn of civilization. Needless to say wood and wood products are still very much with us due to their ubiquity, unique properties and general availability as a relatively cheap and renewable resource. What is perhaps not so obvious is the many new and varied applications that wood is being put to by varying its surface properties through the use of plasma modification. Not surprisingly the contact angle method again comes into the picture in order to characterize the new surface properties. The paper of Dr. B. Riedl of Université Laval entitled   “Influence of Atmospheric Pressure Plasma on North-American Wood Surfaces”, highlights this trend nicely.

We can be sure that the above mentioned topics and many more will be the presented and discussed at the upcoming 10^th in the contact angle symposium series to be held next year. Anyone with further interest should feel free to contact me at the address below.

Dr. Robert H. Lacombe, Chairman

Materials Science and Technology CONFERENCES

Hopewell Junction, NY 12533-6124,    E-mail: rhlacombe@compuserve.com

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Water is everywhere…just not always where we want it. This past winter, the Eastern U.S. was inundated with snow and ice, while California and the Western U.S. are suffering from extreme drought. Availability of water is a growing concern around the world as it is a vital resource for the seven billion (and counting) people on Earth.

While representing only a small fraction of water usage as compared to that used in agriculture and for energy production, industrial use of water is on the rise. A staggering 18.2 billion gallons of fresh water are used every day for industrial use in the U.S. – about 4% of the total water used for all purposes.

Manufacturing one ton of automotive steel requires about 75,000 gallons of water. Actual manufacture of the vehicle itself requires an additional 39,000 gallons. Two and a half gallons of water are needed to produce a gallon of gasoline – and 20 gallons are needed to produce a pint of beer!

Critical part cleaning, for adhesion-related applications, represents a significant portion of industrial water use. Since the replacement of Freon and other solvent cleaning processes starting in the 1980s, U.S. industrial use of aqueous cleaning processes has become the norm.

But aqueous cleaning is a cost-intensive process, whether you’re looking at it from an environmental standpoint, a dollars-and-cents standpoint, or a labor standpoint.

Water needs to be delivered; detergents, surfactants and other chemicals are added and need to be kept in balance to control the washing process; additional processing is required to treat the waste water for recycling or disposal. Rinse water must also be clean and controlled. There is an old saying that “You are only as clean as your last rinse.”

Even after the part has been washed, it is still not ready for bonding, coating, painting, or printing. It needs to be dried, requiring additional energy costs, equipment footprint, time, and labor.

Furthermore, as mentioned above, water tends to not always go where we want it. Even with the best washing and drying processes, water’s influence remains at the molecular surface where adhesion occurs, interfering with a strong bond.

Molecular water resides in the oxides of aluminum and other metals. Water is absorbed and bonded within many polymers such as ABS and nylon. However, water molecules are not usually well-bonded and do not provide a robust bonding surface.

What if there was a better way for critical cleaning of organic contaminants? What if a process did not use water or other liquids but instead actually removed water from the molecular surface while vaporizing organic contaminants? It would be even better if this nano cleaning could be accomplished without touching the part and a chemical activation could occur to chemically bond to the adhesive, coating paint, or printing ink.

Save Water

Stay Dry

Plasma Clean

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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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My colleague, Wally Hansen, and I have just released a new review paper that may be of interest to those of you in the aerospace industry.

As you know, aerospace has had decades of experience with metal bonding, sealing, and corrosion protection. However, many of these methods have not lent themselves well to automation, and they also generate environmental waste.

But new applications are emerging for atmospherically deposited nano coatings that can address these shortcomings. These nano coatings are formed by direct injection of select vapor chemistries into the plasma jet. Such molecular surface modifications yield long-term, environmentally stable interfaces for bonding.

Cleaning

Plasma surface treatment begins with a fine cleaning of the substrate to remove loosely bound organic contaminants (on metal oxide surfaces, the oxide layer is either removed or pre-conditioned for adhesion).

Atmospheric plasma jets provide a multi-faceted cleaning action. First, the charged species within the plasma neutralizes electrostatically bound particles. Next, a vortex of pressurized gas blows away unbound solids and oils. Finally, the substrate is bombarded by reactive gas plasma species.

Low molecule weight contaminants on the substrate surface are efficiently reduced into nascent compounds and removed from the material system. This final phase of cleaning takes place on the molecular scale.

Coating

After cleaning, a different plasma jet technology deposits a functional coating. The coating thickness is controlled by parameters such as distance to substrate and speed. Coatings have been developed that simultaneously provide adhesion promotion and corrosion protection of the bond line. Furthermore, some of these coatings act as reliable tie layers, effectively bridging contact between inorganic and organic systems. There is opportunity to replace liquid primers or otherwise laborious surface pre-treatments used in composite bonding.

So far, atmospherically deposited plasma coatings have demonstrated utility as a release layer, an adhesion promoter, or a corrosion barrier. In practice, the plasma-deposited nano coating combines with conventional protective top coats to amplify corrosion resistance and suppress ingress at damage sites.

The atmospherically deposited plasma coatings show substantial improvement in corrosion performance even at a thickness of less than 500 nm.

Conclusion

Atmospheric plasma cleaning and coating can offer significant advantages in surface preparation of metals and composite systems for bonding and sealing in the aerospace industry. The technology is scalable and amenable to automation as it enables high-throughput material processing.

Furthermore, some plasma implementations are able to combine multiple process steps into a single step while reducing waste and reducing operating costs – without compromising performance.

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Plasma treatments are a permanent and covalent substrate modification.  However many references note diminishing effects of plasma treatments with time.  One generalized conclusion is that the plasma modification is a temporary effect.  This conclusion is not inherently accurate or applicable to all plasma and material systems.  In truth there are many factors that govern the success and longevity of a plasma modification.  Research in plasma lacks harmonization in equipment, setup/configuration, and material selection.  These are key variables in a plasma modification.  Results from one method may not necessarily translate well to another experimental setup or class of material.  For this reason some engineering reviews of gas plasma do more to confound than to elucidate the scientific dialogue within industry.

 

Equipment design is of particular relevance in plasma industry.  This includes but is not limited to the electrode configuration, matching, RF frequency, and equipment geometry.  Many apparatus used in academia boast custom fabricated equipment or custom modification to existing tools.  Their equipment exemplifies engineering capabilities.  In my opinion the effectiveness of the equipment to a material system is specific and rarely generalizable to all materials or apparatus.

 

Plasma chemistry and substrate material should be matched correctly.  Some polymer systems may be either resistant or sensitive to specific plasma chemistry.  It is not enough to report gas, pressure, and power.   A complete characterization should understand the plasma stoichiometry and a hypothesis of the surface interaction.  Furthermore it must be accepted that many polymer systems are mobile, may swell with gas or moisture, or may undergo relaxation mechanisms.  Therefore be careful to consider pairing a material system with appropriate plasma source and plasma chemistry.

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I sell gas plasma technology.

This can be confusing, as there are several types of plasmas, both naturally occurring (such as the Northern Lights, lightning, and stars) and human-made (such as those used in neon signs, fluorescent lights, and plasma televisions).

From the examples above, it’s clear that plasma generates both light and energy. Plasma can also be used to modify – or, more specifically, molecularly re-engineer – other materials.

My company sells plasma technologies and processes for modifying a myriad of materials. Typically, the application is a surface cleaning and activation – either to prepare plastic or metal for a subsequent coating or bonding step — or thin film coatings that may be used to change the barrier or coefficient properties of a surface.

There are many different ways to manufacture human-made plasma.
We use primarily atmospheric and low-pressure plasma technologies in our work. There are a number of benefits to the low-pressure approach:

1.   For starters, the working environment is a primary plasma. In a primary plasma, there is a greater mean free path of the particles before a collision.

This sustained energy is ideal for modifying the interstices of porous media (such as a non-woven or sintered polymer), or for use inside complex nano-scale vias or channels. With atmospheric processes, on the other hand, the mean free path is very short, so the treatment area is limited.

2.   Low-pressure plasma offers chemistry versatility. Many different gases and vapors can be used, safely and economically. Low-pressure plasma is often used as a replacement technology for wet chemistry processes, providing greater control, lower costs, and lower risk of workplace exposures that could lead to accident or injury.

Additionally, unlike many wet chemistry processes, rinsing and curing is not required with a low-pressure process. This means a much shorter processing time, minutes versus hours in some cases.

In atmospheric processes, use of these chemistries may be dangerous and quantities required to generate the plasma may not be economical. This is one of the reasons that our Openair® technology uses just air. It’s incredibly cheap, readily available, and great for many industrial high-speed surface preparation processes.

3.   When using a low-pressure technique, multiple steps may be run in a single process. A part may be exposed to a cleaning gas chemistry (to remove contaminants from a surface) as well as an activation or coating process in a single run. It is not unusual for a single plasma process to replace two to three manual steps, eliminating overhead costs associated with transporting product, labor and materials.

4.   Another advantage is that the low-pressure process provides an extremely controlled environment. The process is conducted in a vacuum chamber with exacting control of gas flow, time, and power. Variations in the day-to-day environment are removed, and the precise process is readily reproducible. Additionally, cleanliness is assured, whether the process is practiced in a clean room or on an industrial manufacturing floor.

5.   Low-pressure technology allows for permanent, stable results. This means that a large batch of parts may be treated and stored prior to use. Or, alternately, parts may be shipped to other manufacturing sites for final assembly.

6.   Our low-temperature process enables treatment of thermally sensitive materials, and the process is free from electrical potential. Therefore, conductive materials may be safely modified.

7.   The total cost of consumables, including energy, gases/liquids, and maintenance parts, is typically less than $5 per hour. Furthermore, there are no additional costs for hazardous waste disposal, as none is created.

8.   The technology offers high-batch throughput:

•   Line speeds, in our standard R2R equipment, are up to 100 fpm with again, no time require for curing or drying steps.
•   Cycle times, during batch processing, range from 60 seconds to 20 minutes. Because a single batch may include hundreds or even thousands of parts, this means that each individual part is treated in mere fractions of a second.

Our job is to accurately evaluate your application and select the most appropriate technology solution for your production goals, be it low-pressure, corona, flame, or Openair. In rare cases, a simple IPA wipe may be all that’s needed to solve your adhesion problems!

Thanks for reading. If you have any questions, I welcome your calls and emails.

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The current generation of consumers will eventually become displaced by the millennials.  Product development and marketing experts will be learning to cope with the new idiosyncrasies of ‘Generation Y’.  Firstly, many of these individuals do not form strong allegiances to brands.  Second, emotional connections appear to have the greatest dominance over consumer selection.  And finally, there is greater importance in first discovery.  The arising rules are reminiscent of a Japanese candy bar shelf; no consecutive month will display the same colors, cartoons, or shapes.  So what are some potential implications to the consumer manufacturing space?  Some trends are already becoming clear.

GenY Automation: versatile robotic platforms continue to be integral in production implementation.  Some of the new mechanization is more mobile, easily programmable, rapidly deployed, and cross disciplined in many different categories of operation.

GenY Materials: Whether olefin or bio-based, the custom polymer formulation could lose attractiveness.  Engineers could abandon the new design of materials with chemistry for more accessible technologies that alleviate material constraints with processing methods.

GenY Fabrication:  3D printing promises new and extremely custom fabrication that are uninhibited by classical machine tools or setup.  DIY design will empower individuals to create niche products for myriad markets.  And after this revolution 4D printing envisions the self-assembly of structures likened to proteins inside living bodies.

GenY Environment: Future consumers assert a greater demand for re-usability and a low environmental impact.  There is a less tolerance for waste in an ever shrinking planet with finite resource.

The manufacturing plants that are best adapted to the changing landscape will claim the lion’s share of consumer purchase.  The challenges will be non-trivial.  On the inside consumer products will require simple molecules that are biodegradable, easily formed, and bond-able.  And on the outside these products may take on radical forms, become regional fads, and short life-cycle.

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Giving back to the community personally and professional has always been important. The challenge however is making the time to have an impact. Through my involvement with groups such as AVS, SVEC  and the SPE local chapter, I as well as my colleagues have been able to expose a diverse group of Bay Area kids and young adults to the varied career opportunities in the sciences, specifically surface modification and vacuum technology. One of my favorite events (tied with volunteering at the Maker Faire) is “Expanding your Horizons.” EYH is a not-for-profit organization that “inspires girls to recognize their potential and pursue opportunities in science, technology, engineering and mathematics.”

The following picture is from this year’s most recent event – with their permission of course. They were actively controlling the vacuum pump and chamber to “measure” the effect of a vacuum on a Peep marshmallow.  This is always the highlight of the day…next to the shaving cream experiment!

It is incredibly rewarding to be in a room with curious young girls and expose them to my “life in a vacuum.”

 

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One of the keys to achieve and comply with lower consumption standards for automobiles thus higher mileage MPG, is to lower the weight of the vehicle. As increasingly plastic substrates are used for constructing a vehicle, including composites materials such as GFRP and CFRP, welding suddenly becomes less of an operational task as opposed to more adhesive bonding.

Adhesive suppliers develop better products to allow for structural bonding while also strategically link up with surface pre-treatment solution providers such as Plasmatreat, to allow for an effective but low cost bonding solution.

Advantages and drawbacks of adhesive bonding for composites*

Compared to mechanical fasteners, adhesive bonding provides many advantages:

• Mechanical fasteners require drilling holes in the parts, and this weakens the composites because it cuts through the reinforcing fibers and also creates weak points. Bonding improves tensile resistance.
• Bonded joints exhibit lower stresses concentrations than mechanical joints when holes are needed, and thus provides increased static strength,
• Risks of cracks propagation are reduced,
• Bonded joints provide always 10 to 25 % weight savings in primary and secondary structures,
• Bonded joints enable the design of smooth external structures,
• For large surfaces bonding costs less than mechanical assembly, because it needs less manpower
• Adhesive may join together all kinds of materials: metals, composites, plastics, wood etc…
• Adhesives can join very thin materials which could not be riveted or bolted,
• Adhesives can join dissimilar materials without the risk of galvanic corrosion,
• Adhesives may be flexible or rigid according to their formulation,
• Adhesives have an excellent resistance to fatigue.

However, adhesives bonding has also some drawbacks:

• Elevated temperature creep resistance is fair or even poor for some structural adhesives.
• Adhesives cannot be used in or near to the motors of automotive.
• In general adhesives do not resist to peel stresses, and this is a  drawback compared to welding for instance,
• Bonded parts cannot be dismantled easily,
• Bonding requires specific design so that the parts will be stressed only in shear mode,
• Bonding requires an excellent and specific surface preparation of the materials immediately before bonding,
• Bonded joints are difficult to inspect in a non destructive manner, although there are several NDT such as X rays, ultrasonic inspection, shearography, and others,
• Structural bonding requires an accurate mating of the parts because adhesives do not give high performances in thick joints,
• Water resistance of adhesives are often only fair,
• Durability of bonded joints must be assessed by difficult laboratory accelerated aging tests.

Pre-treatment with plasma (atmospheric in-line or vacuum low-pressure) can help overcome some of the drawbacks associated with bonding. Many car manufacturers are catching on.  Check out this new article in Automotive News:

http://www.autonews.com/apps/pbcs.dll/article?AID=/20130608/COPY01/306089999/adhesives-sought-for-making-cars-lighter-tougher#axzz2VqlIP6it

Till next time,

Andy

*Source: scribd.com/bonding-of-composite-materials

 

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