Retroreflective Bikes for Safer Riding?

Retroreflective coatings promise safer cycling.

We are all familiar with light reflection — it’s why we can see ourselves in a mirror. Sometimes reflection becomes a distraction, and one solution is to use anti-reflective and anti-glare plastics. Sometimes reflection can be the only way to see an object, such as the moon, in the dark. Reflective paint on the roads and road signs helps us drive and land airplanes at night. What makes reflective paint appear so bright is the presence of tiny particles that use the property of retroreflection.

retroreflectors-diagramA retroreflective object reflects the light back to its source with minimal scattering by sending a nearly parallel ray of light in the direction of the source. There are two simple types of retroreflectors. The first is a corner, or pyramid, reflector, which has three perpendicular surfaces like the corner of a cube. The  second is a cat’s eye reflector, i.e., a transparent ball with reflective back surface. The light reflects back to the source as seen in the diagram.

Retroreflective paints contain small, particulate reflectors as additives. Usually they are small, (0.1 to 1mm) round, highly transparent glass beads. To obtain a retroreflective surface, usually the beads are applied to the surface of wet paint.

SWARCO‘s glass beads with a high refractive index (made from recycled glass from window manufacturers) are incorporated into single- and multi-component liquid paints and polymers. SWARCO’s reflective thermoplastics have extended lifetimes of eight or more years, good for busy city streets.

Prizmalite retroreflective coatings contain specific barium titanate glass microbeads, hemispherically coated with reflective aluminum: “The hemispheric aluminum coating creates the mechanism for retroreflectivity since light passing through the clear half of the glass bead ‘bounces’ off the reflective aluminum-coated back, directing the light back to the source.” The beads are incorporated into the resin as a filler, however, the matrix confines the spheres to the surface due to surface tension. Positioning spheres on the surface is important for reflectivity, since they have to catch the light.

Reflectorized Bicycles

An emerging application of retroreflectivity is reflective coatings for bicycles. At night bicycles can be almost invisible, putting riders in danger. With a little determination, you can “reflectorize” some parts of your bike and by painting it then sprinkling beads on it, following instructables‘ suggestions.

If you don’t want to go the DIY route, Halo Coatings has a patented retroreflective powder embedded in a transparent coating. Halo’s liquid coatings can be applied to plastic, rubber, and other composites.

One the users is the Mission Bicycle Company, which has come up with Lumen, a bicycle with integrated retroreflection:

By coating the entire frame and both rims, the Lumen has more reflective surface area than any existing bicycle solution. Each bike will be painted with hundreds of thousands of microscopic spheres. As light enters those spheres it boomerangs right back to the source. This effect — known as “cat’s eye” — is visible up to 1,000 feet.

The coating, which appears as an iridescent charcoal gray in daylight, is used on the frame and the wheels of this handmade bike.

Will retroreflective bike helmets be next? Maybe, but for now, you can apply a reflective decal or tape to increase visibility!

Image by Sam Beebe.
Diagram by Cmglee.
Source: “Glass Beads. Minireflectors for nighttime visibility of road markings,” swarco.com.
Source: “Retro Reflective Applications,” prizmalite.com.
Source: Paint Your Bike / Bicycle / Gear Reflective!” by goodgnus, instructables.com.
Source: “Lumen: A Retro-Reflective City Bicycle,” by Mission Bicycle Company, kickstarter.com.
Source: “Retro-Reflective Coating Solutions,” halocoatings.com.
Source: “Applied Graphics,” reflectivedecals.com.

What Is Gas Chromatography?

GC lab at Polymer Solutions Inc., Blacksburg, Va.

Gas chromatography (GC) is a very popular chromatography technique used to separate volatile compounds or substances that can be vaporized without decomposition. Alternative names for gas chromatography are gas-liquid chromatography and vapor-phase chromatography. In GC, the mobile phase is a gas (such as helium or nitrogen), which carries the vapors of the compound through a column with the stationary phase (a thin layer of liquid or polymer on a solid support). Typical GC columns are long, often capillary-thin and coiled to preserve space. The vapors of the substance interact with the stationary phase, with each component exiting the column at a different time (called retention time) and detected separately.

The separation efficiency is determined by the properties of the column, such as the chemistry and the polarity of the stationary phase, the column geometry, and the temperature. The individual compounds exiting the column can be detected by a variety of devices, such as a flame ionization detector, a thermal conductivity detector, an infrared detector, and others. Very sensitive separation and detection is achieved by coupling GC with Mass Spectrometry for detection, resulting in Gas Chromatography-Mass Spectrometry (GC-MS).

Wide Range of Applications

GC-MS is a method of choice for forensics applications and is also popular for drug detection, environmental analysis, chemical analysis, food analysis, biochemical and medical characterization, anti-doping control, explosives detection, and for the identification of unknown substances. A visual representation of GC-MS using an example of separation of neutral and acidic drugs is presented in a short video by Thermo Scientifiic:

Food Analysis

Let’s take a closer look at one of the popular applications of gas chromatography. GC has been used for food analysis along with HPLC since the 1950s. One can determine food composition, additives and contaminants, as well as transformation products in food using GC-MS. The method offers rapid analysis of pesticides, antibiotics, growth hormones, bacterial toxins, chemical preservatives, synthetic antioxidants, dyes, emulsifiers, sweeteners, packaging components, and environmental pollutants in food and beverage. Industrial food processing, such as thermal processing, drying, and smoking leave unique markers identifiable by GC-MS, as does unintended spoilage.

Due to GC-MS sensitivity, it is also possible to detect minor changes in a human body related to metabolized food. For example, a recent study performed in New Zealand analyzed the connection of dairy fat intake to the presence of fatty acids in blood. Both milk products and human plasma were analyzed by GC-MS, and 25 fatty acids (four trans-fats, 11 saturated fats, six polyunsaturated fats, and four monounsaturated fats) were detected. While saturated fats and trans fatty acids are considered harmful for cardiovascular health, unsaturated, short and medium chain saturated fatty acids thought to be beneficial for the heart.

In a study, 180 volunteers consumed dairy products, and the fatty acids in their blood plasma were measured in the beginning and the end of one month. Increasing consumption by three servings per day resulted in small increase in the levels of 3 of 20 monitored fatty acids in plasma, while decreasing dairy consumption had no statistically significant effect on the plasma’s fatty acid profile. The authors concluded that dietary advice to change dairy food has a minor effect on plasma fatty acid levels, an unexpected result for our compulsively dieting population … all due to GC-MS!

Source: “Application of Gas Chromatography in Food Analysis” (pdf), by S. Lehotay and J. Hajslova. Trends in Analytical Chemistry, 21(9-10): 686-697, 2002.
Source: “The Effects of Changing Dairy Intake on Trans and Saturated Fatty Acid Levels-Results From a Randomized Controlled Study,” by J.R. Benatar and R.A. Stewart, Nutrition Journal, April 3, 2014; 13(1):32. doi: 10.1186/1475-2891-13-32.
Source: “How GC Columns Work,” by chromatographyvideos, YouTube.

A New Way to Toughen up Elastomers

Scientists have devised a new approach to creating tough elastomers, designing one with interpenetrating polymer networks, stretched to different degrees.

Elastomers (elastic polymers, or rubbers) are capable of recovering their original shape after being stretched. The polymer chains in the elastomers are randomly coiled. When you stretch elastomers, the molecules straighten in the direction in which they are pulled, and when you release them, the polymer chains return to their original, irregular coiled state.

An example of a natural elastomer is rubber, produced as latex (an aqueous suspension of small particles of cis-polyisoprene) by the rubber tree (Hevea brasiliensis). Alternative plant sources, such as dandelions, have been explored. Natural rubber, obtained by drying the latex, has been used for many centuries.

Natural rubber, which is soft and tacky in its original state, was transformed in the mid-19th century with the vulcanization process, which hardens it into a durable industrial product by crosslinking its polymer chains. Vulcanized rubber was used for tires with the development of automotive industry, although synthetic rubber became predominant in the 20th century.

In addition to thermosets, which require vulcanization, modern synthetic polymer elastomers include thermoplastics. Thermoplastics, such as polyurethanes, copolyesters, polyamides, and polyolefin blends, can be injection molded, extruded, blow-molded, or thermoformed. But the high elasticity of elastomers comes at the price of low mechanical strength. Usually this is solved by reinforcing elastomers with particulate fillers, such as carbon black or silica. The smaller the particle size, the greater the strengthening.

A New Approach

Now a totally different and very elegant approach has been used to obtain tough elastomers. A team of scientists from France and Belgium, led by Dr. Constantino Creton, has designed an elastomer with interpenetrating polymer networks, stretched to different degrees. They achieved this using sequential polymerization.

First, they produced a cross-linked rubbery network by UV polymerization of the monomer (ethyl-or methylacrylate) in a solvent. After solvent evaporation, the obtained “single network” was swollen in more monomer, UV initiator, and a crosslinker. The polymer chains in the first network were isotropically stretched from swelling, and the second network was polymerized until all monomer was used, resulting in a “double network.”

To stretch the chains in the first network even farther, the swelling in the monomer and polymerization step was repeated to obtain a “triple network” in which the first network was highly stretched, the second moderately stretched, and the third network was coiled. The interpenetrating networks were interconnected due to the chain transfer during acrylate polymerization. The highly stretched network is sacrificed, or breaks, first during the impact, dissipating energy and preventing crack propagation, as confirmed by incorporating chemiluminiscent crosslinkers that are activated upon breakage. The publication in Science summarizes:

Using sacrificial bonds, we show how brittle, unfilled elastomers can be strongly reinforced in stiffness and toughness (up to 4 megapascals and 9 kilojoules per square meter) by introducing a variable proportion of isotropically prestretched chains that can break and dissipate energy before the material fails. Chemoluminescent cross-linking molecules, which emit light as they break, map in real time where and when many of these internal bonds break ahead of a propagating crack. The simple methodology that we use to introduce sacrificial bonds, combined with the mapping of where bonds break, has the potential to stimulate the development of new classes of unfilled tough elastomers and better molecular models of the fracture of soft materials.

The concept of sacrificial bonds is used in many tough natural hydrogels and other natural highly elastic natural materials, such as spider’s silk. Understood and applied synthetically, it opens exciting possibilities. Now imagine how useful elastomers can be if we combine sacrificial bonds, interpenetrating networks, and self-healing properties! Yes, we learn from Nature.

Image by Lenore Edman.
Source: “Elastomer,” Encyclopedia Britannica, britannica.com.
Source: “Production and Development of Elastomers,” standard-gasket.com.
Source: “A Brief History of Elastomers,” by Stephane Morin, articles.ides.com.
Source: “Toughening Elastomers With Sacrificial Bonds and Watching Them Break,” by Etienne Ducrot, Yulan Chen, Markus Bulters, Rint P. Sijbesma, and Costantino Creton. Science, April 11, 2014, vol. 344, no. 6180, pp. 186-189.
Source: “Materials Both Tough and Soft,” by Jian Ping Gong, Science, April 11, 2014, vol. 344, no. 6180, pp. 161-162.
Source: “Multi-Scale Multi-Mechanism Design of Tough Hydrogels: Building Dissipation Into Stretchy Networks,” by Xuanhe Zhao, Soft Matter, 2014, 10, 672-687, DOI: 10.1039/C3SM52272E.

What are Biomaterials? We Discuss in Denver

Society_for_biomaterialsPolymer Solutions will be in Denver this week at the 2014 Annual Meeting & Exposition of the Society for Biomaterials. This year’s theme is Pioneering the Future of Biomaterials.

What are biomaterials?

Biomaterials can be natural or synthetic substances. They can be used to treat disease or injury to the body, supplementing or replacing tissues and organs. Examples include tissue engineering, drug delivery systems, vascular grafts, and joint replacements. Modern biomaterials continue to be developed to more closely mimic  natural processes within the body.

Resorbable polymers, another name for bioabsorbable polymers, are critical to current, developing, and future innovations of biomaterial technology. The plastics and biomaterials industries have been revolutionized by the development of resorbable biopolymers, including polylactic acid (PLA), polyglycolide (PGA), and polycaprolactone (PCL).

Resorbable polymers are often used with implants and medical devices because they have the ability to slowly dissolve in the body. For example, when used as an implant for maxillofacial reconstruction surgery, the biopolymers dissolve at a rate that allows the body to regenerate itself while the implant is in place, promoting healing and avoiding the use of a permanent plate.

The strength of resorbable materials and their biocompatibility make them an ideal choice for many medical implantable devices. One of the most incredible biomaterial breakthroughs of recent past uses PLA to create bone scaffolds using a 3D bio-printer. The printer’s ink is actually a combination of PLA and alginate, which results in a structure that is hard like bone, but also has cushioned material for cells. Once the bone is printed, it is coated with stem calls. And if it’s not amazing enough that a 3D bio-printer can print such a thing, it is even more amazing how the implant acts in the body. Once the bone scaffold is in place it slowly degrades as a new bone grows, in roughly three months.

Innovations like 3D printed bone scaffolds keep us excited and hopeful about the future of biomaterials and their potential to increase quality of life and better patient outcomes at a global level. We are excited to join other experts and colleagues in the field of biomaterials this week in Denver to discuss the future we all have to look forward to.

Sources:
Syracuse Biomaterials Institute, April 10, 2014.
Biomaterials & Tissue Engineering Department of Biomedical Engineering, Case Western Reserve University, April 10, 2014.
 

Stretchable Circuit Boards For Wearable Electronics

Polymers help in the creation of electronic sensors that conform to the shape of the body.Wearable electronics concepts and designs often exceed our wildest imagination, from stick-on electronics circuits that are flexible enough to wrap around the hair, to the next step: stretchable and twistable working electronic monitors!

Elasticity, i.e., the ability of a material to return to its original shape after deformation, is an inherent property of many living systems, including human skin. Wearable electronics have to mimic the property of skin as closely as possible. Polymers provide a perfect answer to the need of soft sensors and electronics to be flexible. Previously explored concepts included porous polymer elastomers containing liquid metals as stretchable electrode materials.

Stick-on Heart Monitor

Now a totally different approach has been designed and tested in a working prototype of a stick-on heart monitor. An international team of 18 scientists led by Dr. John Rogers of the University of Illinois at Urbana-Champaign used the concept of soft microfluidics to design a technology to create highly stretchable devices using functional rigid electronic components. The article, published in Science, explains:

The most well-developed component technologies are [...] broadly available only in hard, planar formats. As a result, existing options in system design are unable to effectively accommodate integration with the soft, textured, curvilinear, and time-dynamic surfaces of the skin. Here, we describe experimental and theoretical approaches for using ideas in soft microfluidics, structured adhesive surfaces, and controlled mechanical buckling to achieve ultralow modulus, highly stretchable systems that incorporate assemblies of high-modulus, rigid, state-of-the-art functional elements. The outcome is a thin, conformable device technology that can softly laminate onto the surface of the skin to enable advanced, multifunctional operation for physiological monitoring in a wireless mode.

The beauty of the idea is that the electronic components are enclosed inside a thin elastomeric hollow structure filled with a dielectric fluid. Each electronic component is gently attached to the bottom of the enclosure through a “support post.” While the components are mechanically isolated from each other, they are connected electrically by a free-floating network of serpentine-shaped interconnects, which can stretch in a coil-like manner. In their model system, the scientists used silicone elastomer for the substrate and high molecular weight silicone oligomer for the dielectric fluid.

The soft microfluidic electronic assembly successfully withstood 100% biaxial strain and remained fully functional. In response to external deformation, the free-floating connectors can deform with little constraint. This video demonstrates a stretchable electrocardiogram (ECG) device, which wirelessly transfers power, senses electrophysiological potential and transmits data wirelessly to the external receiver. By placing an inductive coil near the secondary coil in the device, the ECG signal is amplified, filtered, and wirelessly transmitted to a receiver and recorded in real time.

Wide Range of Sensors

The quest for soft sensing systems is ongoing, fueled by dreams of seamless prostheses, wearable electronics, and advanced human-machine interactions. Recent flexible and stretchable pressure and touch sensors and stretchable antennas made with silver nanowires are exciting developments, as are previously reviewed (pdf) soft embedded sensors. Curvature sensors can be used to capture motion, and shear sensors are needed to develop functional robotic hands. Above all, autonomous sensors do not need any source of power and transmit data wirelessly, allowing for long-term wearable and implantable electronics. Now, with electronics becoming flexible and stretchable, application horizons are broadening even more, possibly extending an area traditionally occupied by medical devices into fun (and useful) gadgets for everyone.

Source: “Soft Microfluidic Assemblies of Sensors, Circuits, and Radios for the Skin,” by Xu S, Zhang Y, Jia L, Mathewson KE, Jang KI, Kim J, Fu H, Huang X, Chava P, Wang R, Bhole S, Wang L, Na YJ, Guan Y, Flavin M, Han Z, Huang Y, and Rogers JA, Science. April 4, 2014;344(6179):70-4. doi: 10.1126/science.1250169.
Source: “Supplemental Information for Soft Microfluidic Assemblies of Sensors, Circuits, and Radios for the Skin,” sciencemag.org.
Source: “Flexible Sensor Researchers Follow up With Stretchable Antenna,” by Jonah Comstock, mobihealthnews.com, March 19, 2014.
Source: “Experimental Flexible Sensor Tracks Strain, Pressure, Touch,” by Aditi Pai, mobihealthnews.com, January 21, 2014.
Source: “Progress in Soft, Flexible, and Stretchable Sensing Systems,” by Daniel M. Vogt, Yigit Menguc, Yong-Lae Park, Michael Wehner, Rebecca Kramer, Carmel Majidi, Leif Jentoft, Yaroslav Tenzer, Robert Howe, and Robert J. Wood, biorobotics.harvard.edu, 2013 (pdf).

What is HPLC?

High Performance Liquid Chromatography, or HPLC, has been evolving since 1960.

An HPLC module.

HPLC, or High Performance Liquid Chromatography, has been under constant development since 1960. Initially called High Pressure Liquid Chromatography, it overcame the limitations of gravity-driven liquid chromatography, resulting in better component resolution and allowing faster analysis. These two incentives, resolution and speed, have been driving HPLC development since.

High Pressure

HPLC is a type of liquid chromatography with the mobile phase forced through the column by high pressure delivered by a pump. HPLC analysis starts with an injection loop of 5-100 microliters for seamless introduction of a liquid sample into a thin stainless steel column (typically 1-5 mm in diameter and 3-25 cm in length) through vacuum-tight connectors to maintain high pressure through the system.  HPLC columns are often temperature-controlled, i.e., they can be either warmed to improve solubility of the compounds or cooled to ensure the stability of certain analytes.

The pressure in HPLC reaches 6,000-9,000 psi, with a flow rate of 1-2ml/min. The columns are packed with very small particles of sorbent, or a stationary phase (2-50 micrometers). The particles are porous and/or have a chemically bonded phase that interacts with the sample components to separate them. The mobile phase flowing through the column is usually a mix of several solvents and can be either constant (isocratic) or changing (gradient).

Detection and Graphing

The separated components of a sample are detected at the exit of the column using a detecting device, such as a UV/visible, a photodiode array (PDA), a mass spectrometer (MS), evaporative light scattering (ELSD), refractive index (RI), or a fluorescent detector that allows quantitative analysis of the components. The detector output is presented as a graph (chromatogram) on a computer screen or paper strip.

A chromatogram of HPLC analysis of perfume.

HPLC chromatogram of J’Adore perfume water, as example of complex mixture analysis. Separation on C18 column using almost linear 5-100% acetonitrile-water gradient.

HPLC is extremely popular for separating chemical and biological nonvolatile compounds (while for volatile compounds gas chromatography is used). Most compounds are separated by HPLC by using one of the four chromatographic modes: reverse-phase; normal phase and adsorption; ion-exchange; or size exclusion mode:

  • Reverse-phase chromatography is the most popular technique among HPLC methods and is used 90% of the time; it is characterized by a nonpolar stationary phase (C18, C8, C3 column) and water-based polar solvent mix.
  • Normal phase HPLC uses a combination of a polar sorbent (like silica gel) and nonpolar solvents such as hexane for its mobile phase; it is used for separation of cis-trans isomers and chiral compounds, which is especially valuable for the pharmaceutical industry.
  • In ion exchange chromatography the stationary phase in the column contains ionic groups, while the mobile phase is an aqueous buffer. This is a popular method to separate ionic compounds, such as dyes and aminoacids.
  • In size exclusion chromatography, the sorbent is inert and porous, and the analyte molecules are separated by their size, with smaller molecules diffusing deeper into the pores and taking the longest to elute. This technique is most popular for polymer characterization.

 Two-Dimensional HPLC

HPLC is a continuously developing technique, and recently combining two HPLC modes resulted in two-dimensional HPLC (2D HPLC). Developed for protein separation, “multidimensional protein identification technology” uses two chromatography techniques back to back, such as size exclusion plus reverse phase, or ion exchange followed by reverse phase chromatography. An article “Perspectives on Recent Advances in the Speed of High-Performance Liquid Chromatography” describes this trend:

Perhaps the most consistent trend in the development of high-performance liquid chromatography (HPLC) since its inception in the 1960s has been the continuing reach for ever faster analyses [...] Certainly the continued development of ultrafast separations will play an important role in the development of two-dimensional HPLC separations. Despite the relatively long history of HPLC as an analytical technique, there is no sign of a slow-down in the development of novel HPLC technologies.

Every day, HPLC is applied to chemical analysis, pharmaceutical analysis and food analysis in numerous labs across the world. It is an indispensable tool to detect additives in a variety of polymer products and formulations, and versatile enough to analyze food and beverages. It is used to detect  proteins, peptides, amino acids, phospholipids, fat- and water-soluble vitamins, carbohydrates, caffeine, alcohol, organic acids, sweeteners, colorants, preservatives, mycotoxins, herbicides and fungicides, endocrine disruptors, polyaromatic hydrocarbons, synthetic  phenolic antioxidants, dioxins, and polychlorinated bisphenyls (PCBs). From identifying a unique aroma to a detecting a pesticide, you can count on HPLC.

Image by sumos/123RF.
Chromatogram by Lukke.
Source: “HPLC Basics. Fundamentals of Liquid Chromatography (HPLC).” Courtesy of Agilent Technologies (pdf), Inc., polymer.ustc.edu.cn.
Source: “Perspectives on Recent Advances in the Speed of High-Performance Liquid Chromatography,” by Peter W. Carr, Dwight R. Stoll, and Xiaoli Wang, Analytical Chemistry, 2011, 83 (6), pp 1890–1900; DOI: 10.1021/ac102570t.
Source: Food Analysis by HPLC, Third Edition, by CRC Press, editors Leo M.L. Nollet and Fidel Toldra, November 16, 2012.
Video: “High Performance Liquid Chromatography HPLC,” by Royal Society of Chemistry, YouTube.

Conductive Inks Making Their Mark

The production of conductive inks is a growing business.

The conductive inks business is a growing concern, offering both risk and opportunities. According to Research and Markets, the conductive ink and paste market will reach $2 billion in 2014. The market includes both mature and emerging markets with rapidly changing landscape, and an overall predicted 3.2% CAGR over the coming decade. A combination of the right technology and the right marketing strategy is needed for success.

Ink Components

What are conductive inks made of? There are three main components: a polymer binder, a conductive material, and a solvent. After printing, the solvent evaporates, leaving a conductive pattern on a substrate. The materials conferring conductivity to the inks include particles of silver, copper, carbon, and conductive polymers. The applications for conductive inks and pastes are many: touchscreens, photovoltaics, automotive, medical, RFIDs, sensors, and batteries. The current tendency is toward inkjet printing and thin lines, which makes silver nanoparticle inks more and more popular. Other inks and pastes include silver and copper flakes, copper nanoparticles, graphene and carbon nanotubes, PEDOT (polyethylenedioxythiophene), and silver ions and nanowires.

Conductive inks containing silver nanoparticles are characterized by high conductivity, enhanced flexibility and can be screen- or inkjet-printed. Only a few days ago at the Printed Electronics Europe 2014 Conference in Germany, DuPont Microcircuit Materials presented new developments in nano-silver screen-printable ink for Organic Light Emitting Diode (OLED) lighting and other printed electronics. The new ink is intended to make OLED manufacturing process simpler and less expensive. According to an article in Printed Electronics World:

DuPont anticipates that new nano-silver conductor ink materials will be commercially available next year and that these materials will be able to provide a combination of extremely high conductivity and excellent adhesion even after substrate cleaning steps. In addition, it is expected that these new inks would help enable the combination of low print thickness and smooth sintered surface necessary for OLED and optoelectronic applications where deposition of subsequent layers is required.

The nano-silver conductive ink by DuPont will be compatible with both glass and polymer substrates, such as polyimide, polyethylene naphthalate and polyethylene terephthalate, that provide a flexible foundation for OLED lightning panels and flexible printed circuit boards. Other printed electronics from DuPont include a membrane-touch switch, RFID, biosensors, and wearable electronics applications.

DuPont is not the only company to develop conductive silver inks for printed electronics. For example, Creative Materials offers several silver screen-printable inks for a variety of applications including  EMI/RFI shielding of polyimide flexible circuits and membrane switches. In addition to screen printing, the inks can be applied by pad printing, flexography, and rotogravure, are resistant to scratching and flexing, and can adhere to a variety of substrates, including glass, polycarbonate, polyimide, polyester, ITO (Indium Tin Oxide), Teflon, and silicone.

Methode Electronics company (pdf) specializes in nano-silver (and nano-carbon) inks for inkjet printing applications and offers a developer kit to create and verify your designs using a thermal inkjet desktop printer. All it takes is replacing the regular printer cartridge with an inkjet silver cartridge!

Reactive Silver Inks

Some silver inks are actually particle-free. They are called reactive silver inks (pdf) and contain diamine silver complexes, from which silver particles are created on a substrate after printing (upon drying or heat-annealing). Reactive silver inks can be inkjet-printed and sprayed by airbrush.

An interesting hands-on application for everyone is writing or drawing and electronic circuit with conductive ink. A startup company called Electroninks has come up with Circuit Scribe, a water-based quick-drying reactive silver ink, with which you can draw a circuit of your own on regular paper:

From educational fun in classrooms to most advanced technological touchscreens and OLEDs, conductive inks make it possible! Want to learn more? You might want to look into a seminar, “Thick Film Technology,” which is coming up May 6-7, 2014.

Image by germina/123RF.
Source: “Research and Markets: Conductive Ink Markets 2014-2024: Forecasts, Technologies, Players,” reuters.com, April 4, 2014.
Source: “Conductive Ink Markets 2014-2024: Forecasts, Technologies, Players,” researchandmarkets.com March 2014.
Source: DuPont Microcircuit Materials, dupont.com.
Source: Printed Electronics Europe 2014, idtechex.com.
Source: “DuPont Shares New Research on OLED Lighting,” printedelectronicsworld.com, March 26, 2014.
Source: Conductive Silver Inks, creativematerials.com.
Source: Methods Electronics. Nano-Silver and Nano-Carbon Inks, methode.com.
Source: Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) conductive ink, sigmaaldrich.com.
Source: “Reactive Silver Inks for Patterning High-Conductivity Features at Mild Temperatures,” by S. Brett Walker and Jennifer A. Lewis, Journal of the American Chemical Society, 2012, 134 (3), pp 1419-1421; DOI: 10.1021/ja209267c.
Source: Electroninks, electroninks.com.
Video: “Circuit Scribe: Draw Circuits Instantly,” by Electroninks, YouTube.

PSI Groundbreaking Today

WSLS 10 NBC in Roanoke/Lynchburg, Va.

Join Us at 11 a.m. Today

Today is a milestone in the history of  Polymer Solutions. Today we break ground on a new state-of-the-art analytical laboratory and testing facility! Join us at 11 a.m. to watch owner Jim Rancourt, Ph.D., take a shovel to the ground.

This ceremony will be a celebration of our local economy, the support we have received from the local government and officials, and will commence the building of our new facility. The groundbreaking will take place at Lot 8 in the Falling Branch Corporate Park in Christiansburg, Va. (DIRECTIONS).

UPDATE! Thank you to everyone who came out for the groundbreaking! We all had a good time and are excited about our new building. Photos below. We also received a nice write up in The Burgs.

Groundbreaking01-April2014

Groundbreaking-April2014

Polymer Molecular Weight Measurements, Explained by Basketball

Averages can be deceiving -- groups with the same averages may have very different individual members.

By Jim Rancourt, founder and CEO of Polymer Solutions

Molecular Weight and Basketball Teams

NCAA March Madness has gotten me thinking about one my favorite analogies for explaining the various ways to describe molecular weight: basketball teams.

Molecular weight is a critical characteristic of plastic materials. In the most basic terms, molecular weight is the size of the molecule. The molecular weight of a plastic material has a direct bearing on how that material will perform throughout its life cycle and also on the ways a plastic material might fail. For example, when a product is sterilized, the molecular weight may be significantly decreased.  Processing that is not optimized can cause molecular weight deterioration due to the thermal and hydrolytic degradation that can occur during molding operations.

There are many techniques that can be used to measure molecular weight; some provide more detailed measurements than others. The correct analytical approach must be selected with full awareness of the meaning of the molecular weight measurement that will result.  Cue the basketball analogy …

Are Teams With the Same Average Height the Same?

In the NBA there are 15 players to a team roster, with an average height of 6 feet, 7 inches.  If there are two teams that both have an average player height of 6 feet, 7 inches, are they the same?  Not necessarily.  One team could have an entire roster of players each measuring 6 feet, 7 inches tall, whereas another team might have a few extremely tall players and a few shorter players that result in the average.  Would it make a difference in the basketball game, or perhaps the Final Four, if one team has two players that are 7 feet tall?  Absolutely!  The same is true for molecular weight.

The most basic molecular weight measurement is the number average molecular weight, Mn. This measurement is simply an average of the size of all molecules. This measurement is a great starting point for understanding the performance of a plastic material, perhaps to quickly rule-in or rule-out if the molecular weight might be the reason for a plastic failure issue. The analytical technique used to acquire this measurement is Dilute Solution Viscosity (DSV).  It is a relatively inexpensive analytical test and can be performed quickly, with a small amount of sample.  The result of this test will yield a single numerical value that is related to the molecular weight of the portion of the sample tested. The result can then be compared to control samples or known Mn measuresments of the material. If there is no known or expected outcome then it will be necessary to dig deeper, with a more rigorous analytical technique.

By using Gel Permeation Chromatography (GPC), often referred to Size Exclusion Chromatography (SEC), you can determine if the plastic “team” has all 6-foot-7 players or if in fact there are a few 7-footers on the roster.  This technique will drill down to the molecular level and provide a distribution of the exact weight of individual molecules, rather than a single value. The resulting measurements provide the weight average molecular weight, Mw (an also Mn).  This measurement determines if high molecular weight or low molecular weight components skew the overall distribution and can also reveal if the polymer is a blend of several polymer molecular weight distributions.

Image by Polymer Solutions, Inc. and dekanaryas/123RF

What Is Chromatography?

Chromatography used in genetic fingerprinting.

Chromatography used in genetic fingerprinting.

Chromatography is one of the most popular laboratory separation techniques. The name originated from the Greek words “chroma” (color) and “graphein” (to write). Chromatography was first used as a scientific method in 1903 by Mikhail Tsvet, a Russian scientist who applied it to separating colorful plant pigments. Chromatography is also one of the first chemical analysis techniques kids learn in school, as it can be demonstrated in a simplest format using paper and ink.

Chromatography Basics

Liquid chromatography involves several components: a stationary phase (sorbent), a mobile phase (solvent), and an analyte. The analyte is carried with the flow of mobile phase through the stationary phase and interacts with it. If the analyte is a mixture of the components, each component interacts with the stationary phase in a different manner and thus advances through a stationary phase at a different speed. The interaction with the stationary phase determines the retention of each component.

The stationary phase can be either packed in a column (column chromatography), or coated as a thin layer on a solid support (thin layer chromatography). Depending on the size of the column, chromatography can be performed on analytical scale (to analyze the mixture) or preparative scale (to purify a component from the mixture). Paper can be used as stationary phase as well (paper chromatography).

Several types of sorbents can be used as the stationary phase (also sometimes called chromatographic bed). The properties of the stationary phase, along with the properties of the moving mobile phase, determine the type of chromatographic separation. There are several possible types of interaction between the components of the analyte and the stationary phase, which can be used for separation, such as absorption, ion exchange, affinity etc., and all used in different types of chromatography.

Liquid Chromatography Methods

Let’s take a closer look at specific liquid chromatography methods.

The simplest of them is paper chromatography, in which paper serves as the stationary phase, water as the mobile phase, and a mix of water-soluble inks or pigments can be used as the analyte. In real life, if you cry over (or spill some tea on) an ink-written letter, the letters will become fuzzy and form a halo as the water spreads through the paper, driven by a capillary action. With enough liquid, you might see some color separation of the ink components.

One step up the professional ladder is thin layer chromatography (TLC), which commonly uses coats of alumina (aluminum oxide) and silica gel (silicone oxide) on a solid support as the stationary phase, and a solvent, or more often a mix of solvents, as the mobile phase. Selecting right solvent is an art. A  chromatography tutorial from the University of Wisconsin-Madison (PDF) explains:

The eluting solvent should [...] show a maximum of selectivity in its ability to dissolve or desorb the substances being separated. The fact that one substance is relatively soluble in a solvent can result in its being eluted faster than another substance. However, a more important property of the solvent is its ability to be itself adsorbed on the adsorbent. If the solvent is more strongly adsorbed than the substances being separated, it can take their place on the adsorbent and all the substances will flow together. If the solvent is less strongly adsorbed than any of the components of the mixture, its contribution to different rates of elution will be only through its difference in solvent power toward them.

The results of TLC are often visualized under ultraviolet light, offering a rapid and simple technique to analyze reaction products during chemical synthesis. The following video offers a short demonstration of analytical TLC and preparative column chromatography used to separate fluorescent dyes:

Chromatography Columns

Chromatography columns (hollow glass or metal tubes), packed with a stationary phase sorbent are used in multiple modern chromatography methods. In Size Exclusion/Gel Permeation Chromatography (GPC), gel sorbents with different pore sizes are used as the stationary phase. A popular technique to determine the molecular weight of polymers, gel permeation chromatography separates molecules according to their size, with smaller molecules entering the pores and eluting more slowly than the larger molecules.

In High Performance Liquid Chromatography (HPLC), now a favorite laboratory method, the drive for higher resolution and speed has resulted in smaller sorbent particles packed in narrow columns, with a solvent being pushed through the column by the application of pressure. Interestingly, HPLC originally meant High Pressure Liquid Chromatography. High pressure speeds up and improves the separation of different liquid chromatography systems — such as ion exchange chromatography or affinity chromatography — in addition to the previously described GPC, such as.

Chromatography is used to separate a variety of complex substances besides chemical compounds, such as wine, coffee, and tea, providing information about the unique components defining the taste and aroma, and helping us to control the quality of our food and drink. From the simplest dye separation to the most sophisticated biomolecules analysis, chromatography serves us well.

Image by luchschen/123RF.
Source: “Paper Chromatography (PDF),” by Hamid Rajabi, academia.edu.
Source: “Thin Layer Chromatography (PDF),” chem.wisc.edu.
Source: “Methods for Changing Peak Resolution in HPLC: Advantages and Limitations,” by Joseph J. DeStefano, William L. Johnson, Stephanie A. Schuster, and Joseph J. Kirkland, chromatographyonline.com, Volume 31, Issue 4, pp. s10-s18. Apr 1, 2013.
Source: “Sorbents for Chromatography,” VWR, us.vwr.com.
Video: “Chromatography,” by ChemToddler, YouTube.