The second installment in this series addresses the opposite of the first, creating a hydrophobic surface.  First we must ask what they are and why such a surface would be desired.  There are a number of answers but as a colleague of mine wisely says ‘Plasma is not a panacea’.

Hydrophobic surfaces are by-definition surfaces with lower energy states than the 72 mN/m (dyne) energy level at which water is attracted.  In essence, this is a surface water does not like to be on.  Droplets may form through condensation or be placed on them directly, but they will not spread.  They prefer their own level of energy and therefor contract to have the smallest contact with the surface they can muster.  This is what you see when water beads up on the freshly-waxed hood of your car.  The water may be held in place by gravity, but like a kid in the Principal’s office, they don’t want to be there.

So the first thing that comes to mind is that these coatings are designed to keep things dry.  That is the ‘How’, and here are some of the reasons why:  By repelling water on the edges of a case, you are keeping it away from damaging what is inside.  This same property can be used to divert small flows to the areas where you want them in micro-fluidic devices, such as medical test apparatus.  They will also resist water-based liquids such as paints or adhesives and minimize their ability to be permanently bonded to surfaces.  This makes a material easier to clean.

The coatings applied using our PlasmaPlus deposition system are based on the same SiOx chemistry used for hydrophilic coatings, with modifications to the process to make the surface energy as low as possible.  In most cases this is not below the as-molded surface energy of less expensive polymers such at polypropylene or HDPE, but it is much lower than the energy levels of most metals.  For this reason, the hydrophobic properties of these coatings are best used to inhibit corrosion.  They can resist the accumulation of physi-adsorbed water which can be a driver for corrosion.  Due to it’s other bonding characteristics, this same layer can act to promote adhesion in non-water-based systems.  The end result is a water-repellent bondline that is also chemically bonded by adhesive used.  This can be used to seal metal surfaces with much greater reliability than just cleaning and adhesive, thus extending part life dramatically!

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Did you know that PTS is internationally recognized for modifying the surfaces of microfluidic & biological devices?  Check us out on Lily Kim’s www.Fluidicmems.com list of manufacturers.  These partnerships in small devices have a global footprint! Our team’s contribution to the community are elements of advanced polymer chemistry and gas plasma physics; a knowledge that simply translates to targeted conjugation of complex compounds.   We say complex because of the uniquely commercialized methods by which our gas plasma interacts with a substrate.  In some biological applications it is desirable to deliver functional species intact and un-fragmented.  The PTS development lab closely consults its affiliates in how to construct novel surfaces for these new applications.  Although fluidic technologies start micro many need to end big and in high volume.  We make the big or small step using plasma.

My colleague Mikki Larner shared with me a chart illustrating the growing importance of polymeric substrates in the Medical and Microfluidic arena.  Two undoubtedly powerful factors are processing  cost and scalability.

REF:http://www.i-micronews.com/reports/Microfluidic-Substrates-Market-Processing-trends-Market-data/4/217/

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PLASTIC SURFACE MODIFICATION: Surface Treatment and Adhesion, by Rory Wolf (Carl Hanser Verlag, Munich 2010)

Apropos of the upcoming 9^th International Symposium on Polymer Surface Modification it is fitting to review a recently published volume which deals extensively with this topic.

Apart from a brief overview of polymer adhesion issues dealing with inks, coatings and adhesives the book deals extensively with the following plasma related surface modification technologies:

• Flame Plasma Discharge
• Corona Plasma Discharge
• Chemical Plasma Discharge
• Vacuum Plasma Processes
• Atmospheric Plasma Processes
• Ozonation

The treatment of the above technologies is very much slanted toward large scale manufacturing processes such as bare and covered roll operations and a variety of production line configurations designed for large scale output of plastic sheets and/or molded parts.

Table 8.11 from the text, for example, gives a quick overview of the applications of plasma technology. Vertically Listed in this table are more than 40 different items of large scale manufacture such as auto bumpers, tubing, petri dishes, circuit boards… etc. Reading horizontally is a list of 19 engineering thermoplastics that are commonly used to fabricate the items listed and for each polymer one or more recommended surface treatment methods are given.

Thus, say one is interested in treating plastic bottles. Reading from the table we find that polyethylene, poly carbonate, poly ethylene terethalate, polypropylene and poly vinyl chloride are the most commonly used polymers. Reading down the column for polypropylene, for example, we find that flame and plasma are the recommended treatments and that one can expect that the surface energy can be increased from 29 dynes/cm to somewhere in the range of 40-48 dynes/cm.

The number of coating technologies covered is quite amazing. The volume covers some 12 different manufacturing scale coating methods including:

1. Gap coatings
2. Immersion coatings
3. Curtain coatings
4. Rotary screen coatings
5. Gravure coatings
6. Reverse roll coatings
7. Metering rod coatings
8. Slot die (extrusion) coatings
9. Hot melt coatings
10. Flexographic coatings
11. Silk screen coatings
12. Nano coatings

It seems that the number of applications is truly unbounded. My favorite application covered in the book is the Radio Frequency Identification Tags (RFID). These high tech labels look little different from the common mailing variety but contain a small microchip (0.25mm square) connected to a flat antenna all sandwiched between multiple base and overcoat layers which serve to protect the device from the elements and rough handling and further allow it to adhere to the package it is intended to identify. When probed by a nearby scanner the chip can reveal a range of useful information identifying the contents of the package such as product type, color, size, serial number…etc. Interestingly the chip requires so little power it can run on the radiation energy emitted by the scanner.

One can easily imagine a number of delamination failure mechanisms which can destroy the function of such a device including flexing during application and thermal stresses due to large temperature swings (imagine a package being shipped from Miami Florida to Noam Alaska during the northern winter). Thus, not surprisingly, plasma technology is being used to both clean and surface treat the various layers used in the manufacture of RFIDs.

My main complaint with the volume is the rather cavalier treatment of physical data in the numerous graphs given on adhesion strength. No fewer than 5 nonstandard measurement units are in use. Thus we find in figure 7.5 the picturesque G/in units! Figure 5.4 uses the slightly more reasonable g/15mm units, figure 6.10 features N/15mm and figure 5.5 the truly archaic lb/in. Many plots such as figures 6.2 and 6.3 come with no label for the vertical axis whatever. All of this detracts from what is a most interesting and informative volume. One would hope that follow on editions would attempt to standardize the treatment of physical data by using standard SI units throughout.

However, technical misgivings aside, we can enthusiastically recommend this volume to anyone interested in an overview of the truly astounding range of manufacturing processes that are being affected by modern surface treatment technologies and by plasma methods in particular.

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Welcome to our new blog: It is our pleasure to contribute to the Plasmatreat blog site a section dealing with various aspects of surface science and technology and how it impacts various day to day projects dealing with product development and manufacturing. In this regard we have chosen to label the blog as the SURFACE SCIENCE CORNER.

Though the Plasmatreat site deals mainly with issues confronting the open air plasma technology the general aspects of surface science play a vital role in the ultimate success or failure of this methodology as it does also with all other surface modification techniques. Thus the material presented will deal with a fairly wide range of issues of both direct and indirect relevance to the treatment of surfaces with plasmas.

INTRODUCTION

As this is the inaugural issue of the blog it is appropriate that we give a short resume of our backgrounds and how they relate to surface science.
We are Drs. Mittal and Lacombe and our interest and expertise in surface science stems from some 30 years experience in the microelectronics industry. A typical microchip device can consist of a dozen or more layers of insulator, semiconductor and metal materials each on the order of a micrometer or less in thickness. Thus a sizable fraction of the structure can be considered as either a surface or an interface between two surfaces thereby giving rise to a wide range of interactions not all of which are amicable to the overall stability of the device. The microelectronics industry was in fact one of the first to utilize plasma technology on a wide scale both for cleaning purposes and for etching fine lines in photoresists.

Dr. Mittal has mainly focused on writing about and carefully documenting the various aspects of surface science and how they impacted microelectronic technology. He was editor of the Journal of Adhesion Science and Technology from 1987 to 2012 and has also edited over 100 volumes dealing with surface cleaning, adhesion, high temperature polymers, thin films, surface analytical methods and surfactants in solution. This long experience has given him an encyclopedic knowledge of a wide range surface science topics and, very recently, he has started a new journal called Reviews of Adhesion and Adhesives (RAA).

Dr. Lacombe, while sharing the same office with Dr. Mittal for some 7 years, was more a man of the laboratory setting up equipment, performing experiments and carrying out large scale calculations of the thermodynamic stability of multilevel laminate structures. He was among the first investigators to measure the thermal-mechanical properties of 2 nanometer thick monolayer films which were being investigated as the ultimate photoresists already in the early 1980′s. He was also heavily involved in the field of adhesion measurement and has written the only volume dedicated solely to this topic (Adhesion Measurement Methods: Theory and Practice, CRC Press, 2006).

TOPICS

Let us now conclude this introduction with a brief list of the types of topics that will be covered in future issues. Among the topics of most interest are:

ADHESION: One of the primary uses of plasma technology is to alter the chemistry of a surface in such a way as to increase the surface energy and thus significantly improve the adhesion of candidate coatings. Plasma technology has been very effective in this regard. However, it is also important to know whether the level of adhesion achieved is sufficient for the purpose at hand so the topic of adhesion measurement will also be an important consideration.

SURFACE CLEANING: Surface cleaning is another important application of plasma technology and it is also critical to ascertain the level of cleaning attained to know whether it is sufficient or not. Thus measuring surface cleanliness is a further important issue.

SURFACE ANALYTICAL METHODS: The ability to analyze the chemical and physical nature of a surface is of course critical to both of the above mentioned topics. Thus attention will be paid to the various analytical methods used to investigate surface chemistry such as X-ray Photoelectron Spectroscopy (XPS also going under the alias Electron Spectroscopy for Chemical Analysis, ESCA). The thermodynamic nature of surfaces is effectively investigated through the use of CONTACT ANGLE measurements. This rather prosaic measurement technique, though rather simple in concept, is quite subtle in practice and can provide a wealth of valuable information on the physico-chemical nature of surfaces.

BOOK REVIEWS: Our office receives a number of volumes dealing with all aspects of surface science. From time to time when a particularly relevant volume is received it will be brought to the attention of readers of this blog by way of a critical review.

REVIEWS OF IMPORTANT CURRENT RESEARCH: By way of keeping up to date on all aspects of surface science we organize each year through MST CONFERENCES up to 4 symposia which cover the latest developments in this field. From time to time a particularly relevant presentation will be given and such will also be brought to the attention of readers again through a critical review.

Finally let us conclude with a few remarks concerning the style and presentation level of this blog series. Our basic aim will be to make what is arguably a rather esoteric topic clear and understandable to the non-expert by giving concrete examples and also by avoiding technical jargon to the greatest extent possible. Thus we aim for what might be construed as a SURFACE SCIENCE FOR DUMMIES writing style. The aim, therefore, will be to make surface science topics clear and understandable to a range of individuals who have a need to know this topic but may not have either the background or time to pursue the matter at the level of the technical literature. A famous professor once told a student that if he could explain his work to a barmaid then he indeed knew what he was talking about. We will strive to achieve that level of clarity to the greatest extent possible.

Again we are thankful for the opportunity to contribute to the Plasmatreat blog and we hope all readers will find topics of interest and enjoyment therein.

Best Regards,

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

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A recent material society meeting was a real eye opener.  Dr. Ripudaman Malhotra, energy scientist at SRI International, and co-author of the above titled book, presented a fascinating lecture regarding our energy future.

Energy is measured in so many ways that it is difficult to evaluate actual demand and consumption. We have Btu, tons of coal, barrels of oil, and KWh, mostly measured in kilo, mega and giga-huge terms. A new measurement was needed that could be visualized.

Current world use of Oil is about 1 Cubic Mile in volume.  If we compare other energy sources, in equivalents of cubic miles of oil (CMO), we have a current world consumption of about 3 CMO primarily from Oil, Coal and Natural Gas. By comparison, current Solar and Wind renewables contribute a miniscule 0.03%.

At the rate of world growth, there will be a demand for between 6 and 9 CMO in 50 years.  There is currently plenty of fossil fuels remaining but they are from less conventional sources (shale, tar sands) and will be needed while we switch to new sources. A huge task!

 

Producing 1 CMO/ year from alternate technologies will require:

Hydroelectric:                 200 dams – 4 per year for 50 years

Nuclear:                           2,500 plants – 1 a week for 50 years

Windmills:                       3 million – 1,200 a week for 50 years

Solar CSP                       7,700 solar plants – 3 a week for 50 years

Solar roofs                      4.2 billion – 250,000 roofs a day for 50 years.

 

The good news: The sun offers 23,000 CMO/year as heat, wind, photovoltaic and biomass.  The raw material is available. It is time to go to work.

I would like to thank Dr. Ripudaman Malhotra for the use of this data from an extremely interesting lecture.

I recommend the book,  A Cubic Mile of Oil: Realities and Options for Averting the Looming Global Energy Crisis by Crane, Kinderman and Malhotra.

As always, your comments and questions are welcomed.

Regards,

Wally Hansen

 

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Plasma treatment is usually associated with the cleaning and activation of polymers. I would like to highlight the fact that plasma is also a very effective way to clean and activate metallic surfaces.
When an adhesive or paint is applied to an aluminum surface, the bond actually happens between the adhesive and the oxide layer that is present on the aluminum. Naturally forming aluminum oxide is an unstable, and non-uniform, surface to bond to.
By using atmospheric plasma as a pre-treatment to aluminum, not only will the contaminants be removed in exactly the same way as they are on polymer surfaces, but the density and stability of aluminum oxide layer as well as its associated hydroxyl group concentration will be increased.
This resulting new layer will allow for the formation of covalent bonding of the adhesive to the aluminum.

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This plasma may be reminiscent of summer or tequila sunrise, but is beautiful bright plasma always a good thing?  The unique spectral emission of a gas or vapor plasma results from the relaxation of electrons from their excited states.  Electrons form discreet orbits around the nucleus of an element or compound.  Energy is released in the form of light when an electron falls from a higher energy state to a lower energy state.  The distance the electron fell governs the wavelength of the light that is emitted.   But how important is the intensity of the glow? The more energy you put into a system the greater the intensity of the glow and the concentration of reactive species.  But this does not necessarily mean a greater degree of surface modification.  Ions generate friction and if the mean free path is not sufficiently small then heat may disrupt or reorient the polymeric surface that is being modified.  Too much energy is also responsible for ablation and fragmentation of compounds and/or larger molecules.  Too much fragmentation of a surface may leave you with a weak boundary layer.  Pulsed power and low duty cycles make for less interesting plasma.  But in a lot of situations this helps preserve the chemical structure of the matter being constructed.  Controlling the energy and energy delivery is often important when it comes to custom polymerization of ultra thin coatings.

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Hello again packaging professionals.

In this post I am going to briefly touch on the cost savings and ROI enabled by plasma treatment in the folding carton industry.

There are multiple opportunities for cost savings with the implementation of plasma treatment.   One of these is the ability to floodcoat UV coated boards and bond directly to the coated surface instead of cutting printing blankets to allow for good glue adhesion.   A facility that can save 20 blankets per month can pay for a single jet plasma system in less than 8 months on that savings alone.

Another major area of savings is adhesives.   Plasma treatment of UV coatings or poly coated boards can allow manufacturers to change from holt melt to cold glue.   In addition, less glue may be required to achieve the same results.   Implementing plasma treatment on difficult to bond jobs can also allow for the use of the same cold glue plantwide, eliminating the need for multiple adhesive types (including more expensive alternatives that were used in the past).

Plasma treatment can greatly enhance productivity as well.   It has been seen in real world trials and in current production applications that plasma treatment can help increase line speed by as much as 100%!   This is obviously a huge savings especially on large jobs where multiple millions of cartons are run through a folder-gluer.

Lastly and possibly most importantly is the increase in bonding quality that results from a plasma treatment.   As discussed in previous posts, plasma treatment allows for true chemical bonding between the substrate and adhesive.   This provides bonding strengths that have never been seen before in the industry.   Trusting the bonding of folding cartons to old methods and hoping they work is very risky business.   One rejection claim from a customer can pay for several plasma units!

In an ever more difficult manufacturing environment, plasma treatment is the natural choice that allows facilities to progress and reach their financial goals much quicker as they face more cost pressures from their clients.

That’s all for now.   My next entry will focus on food and pharmaceutical packaging applications.

Thanks for your attention.

Shaun Glogauer.

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We get many inquiries regarding our coating technology.  Hydrophilic, hydrophobic, insulative, protection from the elements; you name it, there is someone out there that is looking for the tailored properties I’ve mentioned and more.  All mentioned are possible with our technology, however not in all scenarios and material combinations.  Is a series of blogs I will attempt to address the typical end goals of customers and where we can help the most.

Hydrophilicity is the most common request, and we can satisfy it via a few methods.  It is a measurement of how easily water wets out across a surface which is also a measurement of how functional (receptive to bonding) that surface is.  Our standard atmospheric plasma will typically elevate the surface energy of a material to a point well in excess of 72 dynes, which is where water wets out across a surface.  Similarly, we can deposit a glass-like nano-layer and elevate it’s surface energy to above 72 dynes as well.  The reason to use this coating rather than activate the material directly is that not all materials have strong longevity of treatment or are chemically receptive to all material combinations. Softer materials or those with many additives may only hold treatment for a few minutes before observing a drop. However if you properly adhere the coating to the surface while it is freshly activated the coating will be permanently adhered.  This layer can in turn be activated and will exhibit great longevity of treatment and can provide a necessary link between dissimilar materials.

The surfaces will only stay active/clean if you keep them that way.  A highly functional surface with oil smeared on it is now an oil surface. Additionally, that oil has likely rendered the plasma treatment neutral, requiring another cleaning and functionalization (whether by coating or just standard plasma). Luckily, with plasma there is little concern with treating a part again and you can regain the desired properties with ease.

By coating the work piece you have chosen the surface you want rather than having that be dictated by your material choice.  This opens up the design process as ‘design for assembly’ often means choosing materials that are easily bonded and now that can be almost any material with a PlasmaPlus coating!

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