The term polymer sometimes refer to plastics, but also encompasses a large class comprising of both natural and synthetic materials. Some natural materials are: shellac, amber, natural rubber and cellulose. There are many synthetic polymers consisting of  many types of plastics, man made rubbers, epoxies and resins. Some examples are synthetic rubber, Bakelite, neoprene, nylon, PVC, polystyrene, polyethylene, polypropylene, polyacrylonitrile, PVB, silicone.

A Metal-filled Polymer is: A polymer filled with metal particles such as Nickel, Copper, Graphite, Silver and other metals. Conductive Adhesives are a type of metal-filled polymer commonly used to repair or bind things to metal surfaces.  Both are widely used because of there unique properties. Metal-filled polymers’  mechanical properties and processing methods are typical of plastics but exhibit electrical characteristics similar to metals, due to the metals that are mixed in. As a result they can be compressed, shaped, hardened, softened, and more using temperature variance. Controlling these aspect allows for a wide range of applications.

Applications

Because of these properties, metal filled polymers and conductive adhesives are commonly used for rebuilding, repairing, protection, prevention, bonding, and sealing of metal objects (such as pipes, washing machines, etc). They also can serve as conductive inks, which can be used for printing circuits.

Metal filled polymers can effectively be used for surface mounting and other electronic component assemblies. Instead of using traditional soldering that contains lead, using conductive adhesives both increases the integrity of circuits and allows engineers to perform “cold” soldering. Nifty products such as LED glass are created by mounting surface LEDs onto glass using conductive adhesives and circuit printing.

There exist many suppliers of conductive adhesives and metal filled polymers (usually referred to as metal filled epoxies). The following lists a few of them:

1. ITW Devcon – local corporation: 30 Endicott Street, Danvers MA 01923
2. Hy-poxy – hy-­poxy-­systems.amazonwebstore.com
3. Epoxies, Etc - http://www.epoxies.com/
4. Cool Polymers - http://www.coolpolymers.com/eseries.asp
5. Polysolder - http://www.cooksonsemi.com/products/polymer/polysolder.asp“

Safety

So I am going to write a little about the safety concerns when handling some of the metal-filled polymers and conductive powders we found.

With Plastic Steel (http://www.devcon.com/), a metal-filled epoxy used as a bond or sealant in the rapid repair of metal surfaces and equipment, it is a moderate skin irritant.  Contact at elevated temperatures can cause thermal burns, which may result in permanent damage. Extensive contact may also cause skin sensitization (itching, redness, rashes, hives, burning, swelling). It is best to handle this with no direct skin contact. The same applies to the other associated products in this class of materials, including Aluminum Putty Resin and Aluminum Liquid, Titanium Putty, Bronze Putty and FasMetal Alumina-filled Putty.

Plastic Steel has low vaporizations, but some of the other products in this class are toxic at sufficiently high concentrations, and maybe cause dizziness, headache and anesthetic effects, even trigger asthma-like symptoms in susceptible individuals. It is best to use these in a well-ventilated room, rather than in a completely closed environment.

Conductive metallic powders may cause irritation to the eyes, skin, and respiratory tract, as will metal-filled lacquers such as Cosmichrome (http://www.goldtouchinc.com/). In addition, powders at a sufficient powder-air concentration may ignite in the presence of a heat source. Care should be taken to avoid accumulations of dusts or powders in places where these accumulations could cause shorting of electrical switches, circuits or components

Uses in Art and Design:

Due to the wide range of applications there are some interesting uses of Metal-filled Polymers and conductive adheasives in art and design. MR Shock absorber are one example. MR Fluids are oily flids that when exposed to electric currents become viscus due to the electro manganic particles contained in the fluid. “Because the current can be turned on and off in milliseconds, the oily liquid transforms itself from a liquid to a solid and back again so instantaneously that is can significantly dampen shock from potholes, speed bumps or washboard roadways”  http://www.djc.com/news/ae/11151055.html.

EM Shielding is another interesting use in design. Du to excessive cell phone use, Ipods and other wireless devices, we are becoming increasing aware of and concerned by EW pollution. Conductive Polymers can function as shielding from these waves in elements like windows by coating them with a EM absorbing paste. PDF .

A third Example could possibly generate power though your shoes. Flexible generators or comprised partly by Metal-filled Polymers and have the ability to create energy when deformed. “Unlike traditional piezoelectric generators, which require quick, subtle motions to generate power, artificial muscles are better tailored to the “large, slow motions” we perform every day”. Ecouterre article.

Here is our PDF:

MetalFilledPolymers_ConductiveAdhesives

By Dena Molnar, Daekwon Park, Jill Sherman

Introduction

Applications of Carbon Nanotubes are an exciting area of exploration in that they display a number of  performative qualities and they are still considered a relatively new discovery (about 20 yrs old). Aside from their extreme mechanical strength, the electronic properties of CNTs, which can be either metallic or semiconducting, make this a unique material. High thermal conductivity and chemical resistance are additional qualities. Together, the properties of this material lend itself well to sensory and actuation applications, field emitters, semiconducting components, energy storage devices, and have broad implications for use in the product design, architecture and textile fields.

Structure and Properties

Carbon is unique among the elements in its ability to take on many different structural formations. Carbon nanotubes or CNTs are part of a class of carbons referred to as Alltropes of Carbon. Alltropes of carbon are the different molecular configurations (alltropes) that carbon can take. Put another way, Carbon nanotubes are essentially rolled up tubes of carbon atoms.

The hardest known alltrope of carbon is diamond, while one of the softest is Graphite, or “graphein”, which is conductive and the the most common form of carbon nanotube.

Thermal conductivity- Carbon-based materials, diamond and “in-plane” graphite display the highest measured thermal conductivity of any known material at moderate temperatures.

mechanical properties- Nanotubes are recognized for their strength (one of the strongest materials known) and elasticity. Single walled nanotubes are most commonly used because they can be grown with fewer defects and are, for this reason, stronger. Because nanotubes are essentially  ”rolled up” graphein, they are capable of elastic deformation, where the shape of the nanotube may change, but the local structure does not. While they are also capable of local and irreversible deformation on the atomic level, they can bend reversibly at very high angles and their tensile strength is unmatched.

electrical properties- Carbon nanotubes can be either metallic or semiconducting. This is advantageous because  metallic conductors may burn up or out more easily. “Whether a nanotube is a metal or semiconductor depends on the properties of the electrons in the tubes. Carbon nanotubes are unique in that small differences in their diameter and chirality affect whether it is a metal or a semiconductor. For most other materials, its metallic or semiconducting nature depends mainly on its chemical composition and the 2-D arrangement of atoms and molecules”. Physics Graphics: http://www.aip.org/png/html/nanotube.htm

Adhesion – The aligned growth of CNTs allows for highly adhesive technical surfaces to be generated, which work according to the Van der Waals force.  This is the same principle behind why a gecko can stick to glass surfaces. The contact surface area provided by these vertically aligned tubes is large enough that forces of attraction act between the ends of the nanotubes and the molecules of the substrate.

Varieties and Applications

Although large scale applications of CNTs are well documented. (ie. as an additive for increasing the strength of plastics), their potential in smaller applications and in the creative realm is still being explored. Examples of novel applications are listed below:

-As sighted in “Smart Surfaces”, by Thorsten Klooster, researchers at Rensselaer Polytechnic Institute have developed one of the darkest known synthetic materials via the controlled growth of nanotubes. This material only reflects 0.15% of incoming light, compared with traditional black pigment, which reflects between 5-10%. The high level of absorption is attributed to the vertical positioning of the nanotubes and their “porous” quality, allowing light to penetrate further into the surface.  Greater levels of light absorption is of interest for efficient solar energy conversion applications. Link to pdf - RPI

Conductive nanotube ink, polymers, and thin films are on the market .

Resources

Below are a list of links to Resources to obtain various components containing Carbon Nanotubes. Additional pdfs with process, specification, and safety guidelines are also included.

SWeNT

Producer of ready to use Carbon Nanotube Ink for Screen Printed applications  http://swentnano.com

Printing process recommendations  SWeNT

Structure and Applications

Nanotube Ink Specifications

Product Identification and Safety

NanoLab

Producer of Carbon Nanotube Inks for the printing of nanotube electronics and sensors.

http://www.nano-lab.com

Buckypaper http://www.nano-lab.com/buckypaper.html

Nanotube Ink http://www.nano-lab.com/nink.html

US Research NanoMaterials, Inc

http://www.us-nano.com/

Papers/ Articles

Thermal properties of carbon nanotubes: Thermal_conductivity

Mechanical and electrical properties of carbon nanotubes: Mechanical.Electrical

Carbon Nanotube dye may put a capacitor in your Shorts: http://arstechnica.com/science/news/2010/01/carbon-nanotubes-bind-to-fabric-to-make-wearable-electronics.ars

Conducting Textiles from single walled carbon nanotubes:

http://www.sciencedirect.com/science/article/pii/S0379677907000914

Carbon Nanotube Thread: http://www.technologyreview.com/computing/21689/

Class Presentation - Carbon_Nanotubes

I. Introduction.

“Elastomers,” from the combined terms “elastic” and “polymer,” encompass a broad range of rubber and rubber-like materials, with conductive particles embedded inside—making them conductive composites. Since they’re highly mold-able and naturally highly resistant, elastomers are widely used for their insulating or dissipative properties.  However, precisely because they’re so pliable—they can be shaped and extruded into almost any desired form, where metals can be limited and/or pricey—they’ve become desirable as conductive materials as well. Elastomers are used for their conductivity properties in four ways:

Insulating (e.g. wire coating)

Dissipative (“anti-static” polymers)

Conductive (materials capable of conducting modest amounts of electrical current)

Highly Conductive or Shielding (materials capable of conducting significant amounts of electrical current)¹

The range of conductivity is pretty wide, requiring different materials for different conductivity rates:

For modest conductivity (surface resistivity 10³ to 10⁷ ohms/square) “conductive carbon” additives are generally used very cost effectively. For highly conducting thermoplastics  (surface resistivities of 10² ohms/square and higher) carbon or stainless steel fibers are often necessary.²

II. How does it work?

Elastomers act as a “film” against a conductive “filler”; with enough filler present, elastomers transform from insulating materials to conductive ones. Filler material can be nickel, silver, aluminum, glass, or other materials.

Even with highly conductive filler material, however, conductive composites always maintain resistivity several orders of magnitude higher than the pure filler material.  So refinements in the research have sought to understand all influences on conductivity—beyond the intrinsic conductive properties of the filler material itself. Influences on conductivity include the size of the filler particles, their relative hardness, and the rate and intensity of contact among particles:

Resistivity increases with increasing filler hardness and/or elastic modulus and insulating film thickness, while resistivity decreases with increasing particle size and intrinsic stress.³

Resistance occurs in three different forms: the base-line, intrinsic resistance of the filler material and polymer; the constriction resistance (when small areas of passage constrain the flow of electrons); and tunneling resistance at the point of contact, where particles of filler meet and must “tunnel over” the film of polymer.

III. Types & Examples

The most common uses for these elastomers are for connecting and shielding mechanical parts—for example, with a gasket as a buffer between two working elements—while retaining enough desired conductivity. Some common use areas include:

Electronic Enclosures
Computer Enclosures
Cell Phones
Hand Held Devices
Network Routers
Medical Diagnostic & Analytical Equipment
Aerospace & Automotive
Electronic Systems
Indoor & Outdoor Enclosures

Such wide usage means you can find all shapes and sizes on the market, and there are custom-order services available. Gaskets, shields, tubing, cords, O-rings, sheets—all of these forms are readily available. (A sample kit from EMI costs $79 and quotes are available for orders; do note, however, that most items require a minimum of $250 per order.)

You can also get conductive foam ($30 for a 6-inch square), conductive elastic fabric ($30 for a piece 12 x 52 inches); and stretch-sensing rubber, narrow cording that’s embedded with carbon particles ($13 for a 10 cm length, 2 mm in diameter). Note, too, that some tech-fabrics contain polymers and can be threaded with conductive materials.

And this conductive foam sensor ($8 for a 12 x 12 x 1/8″ sheet) is modestly conductive, but its resistivity is decreased when compressed—so it can detect changes in pressure, easily measured by simple electronics.

There are ambitious projects in the works for conductive elastomers as well. Stanford researchers have created an electronic synthetic skin, using organic electronics with an elastic polymer stretched over it:

Researcher Zhenan Bao, chemistry professor at Stanford, and her team “used organic electronics – with an elastic polymer called polydimethylsiloxane (PDMS) – to make their electric skin, which is 1,000 times more sensitive than human skin:

Bao took a piece of PDMS measuring six centimetres square with pyramid-shaped chunks cut out of it at regular intervals. When the PDMS is squashed, the pyramid-shaped holes that were previously filled with air become filled with PDMS, changing the device’s capacitance, or its ability to hold an electric charge.

To make it easier to detect the changes in capacitance, Bao stuck the PDMS capacitor onto an organic transistor, which can read out the differences as a change in current. The team used a grid of transistors to track pressure changes at different points across the material.³

Here’s more on this project, as well as a second prototype in development by a team at UC Berkeley. And here’s the video with the skin’s extraordinary sensitivity demonstrated by researchers:

In addition, there are ongoing research initiatives using conductive elastomers: graphene composites, which present great promise for computing applications, and metal rubber, a highly conductive and flexible elastomer that can be mechanically strained to 1000% of its original proportions while remaining conductive.

V. Safety issues

VI. And a last speculative thought:

There’s been a lot of interest in Sugru, a durable silicone rubber that molds to any shape for any purpose.

It “cures” at room temperature, but it maintains some flexibility, so it can hold together things that still need to move, like wires, cables, etc. In its natural state it’s not conductive, but this is such a DIY material goldmine that it’s worth putting out there: What might be ways to make this conductive, and for what uses? You can buy 12 minipacks, 5 grams apiece on the Sugru site.)

Sources:

1. & 2. 3M on conductive polymers

3. Ruschau, G. R., Yoshikawa, S., and R. E. Newnham, “Resistivities of Conductive Composites.” Journal of Applied Physics. 72:3, 1 August 1992. Materials Research Laboratory, Pennsylvania State University, University Park, PA.

Link to the conductive elastomers presentation slides (PDF).

Conductive ink is a rising technology that is making circuitry available to a larger audience than the traditional method.  The ink can be inserted into a standard roller-ball pen which is highly available, cheap, and precise.  This pen can then be used to write on paper.  Paper is perfect for circuits because it is available, inexpensive, lightweight and biodegradable.  Also because paper can be manipulated into 3D configurations, it increases the possibilities for using conductive ink.

Silver based conductive ink is the most effective conductive ink available to us.  Unfortunately, silver is very expensive and its price fluctuates too much to be stable (Developments in Conductive Inks).  It is made of mostly silver (about 45-55% of the total solution).  This percentage insures the right viscousity so that the ink flows without leaking or clogging.  Also, it can be wriiten on soft and hard surfaces.  The other 45-55% is the fluid solution composed of Diethanolamine and Hydroxyethyl cellulose.

hlt.media.mit.edu/cmi_readings/conductorsPapers/conductivePen.pdf

Silver based conductive ink is highly conductive (it’s mostly made of silver flakes and particles).  It’d resistivity decreases after drying.  After 30 minutes at room temperature, the resistivity is 1.99×10^(-4)ohm-cm.  Impressively, the paper on which a silver based conductive ink circuit has been printed on can be folded and bent many times without affecting the conductivity.

Due to the expensive price of silver, silver based conductive ink is not very popular with the general public.  It’s most common use currently, is to make the RFID tags (like the one pictured below).

However, based on the rising popularity of printed circuits over the traditional methods, this technology can be applied to anything.  There are already prototypes of interactive wallpapers, books, paintings, and clothing.  Also, because these circuits can be printed on almost literally anything, the cost and time for manufacturing circuit boards and prototyping projects can be reduced.

As useful as this ink is, it has some health risks.  The main component is, of course, silver.  Silver is actually antibacterial and is often used in the medical field (tooth fillings, topical gels and bandages).  However, if large quantities are inhaled or ingestid, it can cause argyria (blue skin).  One example is paul karason – Google Search.  Silver also has less dramatic side effects such as seizures, fatigue and stomach distress.

Other components in silver ink are also only dangerous if ingested in large quantities, and are commonly used ingredients in cosmetics.  One of these is called Diethanolamine, a common ingredient that is responsible for the creamy texture and foaming action in shampoo and cosmetics.  Another ingredient is Hydoxyethyl Cellulose, also used in cosmetics and household cleaning products.  It is frequently used with hydrophobic drugs to assist dissolution in the digestive juices.

Silver based ink can be acquired from these retailers:

M.E. Taylor Engineering, INC.

Silver Paint, 18% Silver, 15 gram brush-cap bottle

SRA Soldering Products and more

Silver Ink 50 gram kit > Silver Epoxy and Silver Paint > Electronic Chemicals > Main Section > SRA Soldering Products

CAIG Laboratories, INC.

CircuitWriter™

And of course, Amazon, INC.

Amazon.com: conductive ink: Electronics

If you are interested in a safer conductive ink, check out the Bare Conductive Ink group at: Welcome – Bare Conductive

Bare Conductive Ink is nontoxic and can be applied to the skin for incredible projects like The Humanthesizer.

Presentation: Silver Ink Presentation