Heat Reactive Materials
Heat reactive materials change state, shape and/or color when exposed to temperatures above ambient. Naturally, many materials change shape, eg. melt, at high temperatures. What’s special about some of them is that their state, shape and/or color can be altered at relatively low temperatures (provided through hot water, body heat, hair dryers, ambient heaters, ovens, or just a hot summer day), making them easy to use and suitable for DIY projects. In this post I’ll go over thermochromic pigments and a few materials they have been incorporated into, namely paint, fabric, film and glass.

Thermochromic Pigments change color when exposed to heat and turn back to their original color when the temperature drops again. According to TEP:

Most thermochromic materials are based on liquid crystal technology. At specific temperatures the liquid crystals re-orientate to produce an apparent change of colour. The liquid crystal material itself is micro-encapsulated - i.e., contained within microscopic spherical capsules typically just 10 microns in diameter. Billions of these capsules are mixed with a suitable base to make thermochromic printing ink or, for example, plastics destined for injection molding.

These pigments can be mixed with an acrylic base or screen printing ink. At room temperature the pigment appears in its original color, but at temperatures between 27° and 30°C (80° to 86°F) this color disappears, eg, if a black pigment is applied to a white surface, the surface turns from black to white at the change-over temperature. When mixed with an acrylic base each pigment will turn instead into the color of the acrylic base or color blender, eg., if a blue pigment is mixed with a yellow acrylic base the resulting color will be green, but at the change-over temperature the blue will disappear and the green will turn into yellow. The ratio of acrylic base to coloring pigment depends entirely on the application and density of color required. For a detailed explanation of the functioning and applications of thermochromic pigments see the TEP Smart Colors info sheet (PDF) and this little demo animation.

Shi Yuan’s thermochromic wallpaper

Temperature-Sensitive Glass results from the application of thermochromic pigments to glass tiles which change color based on ambient, body or water temperature:

The textured glass surface layer protects and highlights the color-change film on the tile. The base color of the tile can match almost any color, and the temperature change point can be fit to the user’s environment and requirements. The dynamic color change begins at the selected activation temperature and shimmers through three phases, one with each 6–10° rise in temperature. Once the temperature peak is passed, the base color returns and remains the same until the temperature drops.
(source: Inventables)

Temperature-sensitive glass tile (image by Inventables)

Thermochromic Film has adhesive on one side and thermochromic ink on the other. The film is normally black but changes to bright green/blue at temperatures between 29.4 and 33°C (84º - 91º F). Due to its low change-over temperatures, touching a piece of thermochromic film for a few seconds will cause the contact area to change color - it can also be used with nichrome or any other heat source.

Thermochromic film (image by Mindsets)

Suppliers
Body Faders (US) :: thermochromic fabric
Inventables (US) :: thermochromic fabric, thermochromic film, temperature-sensitive glass tiles
Mindsets (UK): thermochromic pigments, thermochromic film
Paint with Pearl (US) :: thermochromic pigment powder

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If you’d like to contribute content or corrections regarding thermochromic materials, please use the comment form below.

>> about the materials 101 series.

photochromic pigments from mindsets

UV reactive materials, which initially have an off-white appearance, change to bright colors when exposed to UV rays (sunlight or a UV lamp) and revert to their original pale color when away from UV light. The basis for these materials are photochromic pigments which can be mixed with an acrylic base and then applied as normal paint. The more dilute the pigment, the less dramatic the color change.

acrylic base to orange photochromic pigment ratio tests ran by a student of the Aix-en-Provence (France) Art School

Besides pigments, which can be used to make color-changing paints, photochromic materials are also available in the shapes of sewing and embroidering thread, plastic goods such as beads and buttons, and nail polish. Naturally it’s also possible to produce photochromic fabrics, but I haven’t been able to find them as raw materials in retail shops.

photochromic thread and beads (indoors and outdoors)

What is it exactly?
According to Wikipedia:

Photochromism does not have a rigorous definition, but is usually used to describe compounds that undergo a reversible photochemical reaction where an absorption band in the visible part of the electromagnetic spectrum changes dramatically in strength or wavelength. In many cases, an absorbance band is present in only one form. The degree of change required for a photochemical reaction to be dubbed “photochromic” is that which appears dramatic by eye, but in essence there is no dividing line between photochromic reactions and other photochemistry.

Suppliers
:: Mindsets (UK): photochromic pigments and sewing thread
:: Solar Active (USA): UV reactive sewing and embroidering thread, plastic goods (beads, buttons, etc.), nail polish

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If you’d like to contribute content or corrections regarding UV reactive materials, please use the comment form below.

>> about the materials 101 series.

As the name indicates, electrotextiles are textiles with electrical properties. They’re mostly used for electromagnetic shielding, anti-static and heating purposes, and also for soft circuits: electric circuits or sensors made out of a combination of special fabrics, threads, yarns and electronic components.

:: conductive fabrics
:: conductive threads & yarns
:: special electrotextiles
:: related materials
:: starter kit
:: electrotextiles tutorials by openMaterials
:: learning resources
:: main suppliers

Conductive Fabrics
Fabrics with electrical properties made by blending or coating textiles with copper and/or nickel and/or silver fibers. They’re available in many textures, weaves and combination of materials. Stores such as Plug & Wear, Mindsets and Less EMF sell kits with a sample of each of their conductive fabrics. These samples provide an excellent way to get a hands-on feel for and test the properties of each material in order to find the right one for your project before acquiring it in a larger quantity. There are many types of conductive fabrics and you can find an extensive (though not comprehensive) list on the oM wiki. Here I will only describe some of my favorites.

:: Shieldit Super (iron-on conductive fabric) from Less EMF: a single side conductive fabric made of polyester substrate, nickel and copper. The back side is covered with a non-conductive hot melt adhesive, which activates at 130ºC (266ºF), meaning that it can be ironed on to another fabric, wood, glass or paper. This fabric is a pretty good conductor, easy to apply and thus perfect for making longer connections between components. It can also be cut and sewn like ordinary fabric. 230 g/m², 0.17 mm thick. UL 94V-0 level flame retardant. RoHS Compliant. Gray, 14 inch wide.

:: Electrolycra from Mindsets: looks and feels like ordinary lycra but it’s highly conductive. Its conductivity in one direction depends on how tightly it is stretched - if you pull it the resistance increases and then drops again when stretched even tighter. When cut into a thin strip, the material also warms up when current is passed through it and can thus provide the basis of a heated garment. A 6V battery will cause an appreciable warming effect. Resistivity: 5 ohms per 100mm, increasing to 20 ohms when stretched to 150mm. If the material is turned through 90º and stretched the resistance drops to 2.5 ohms.

:: Knitted Superlight Conductive Fabric from Plug & Wear: an extremely light and transparent conductive fabric, only 190 g per sq.m. It allows air flow and is easy to cut with scissors. It can also be sewn with a standard sewing machine or soldered to. Hand washable. Material: tin copper. Resistivity: 0.1 Ohm per square. Width: 1000 mm (39″), thickness: 1 mm (.039″), max working temperature: 150°C (302°F), weight: 190 g per sq.m.

:: Conductive Aluminum Laminated Fabric from Plug & Wear: a single side conductive (the shiny side) laminate made of aluminum foil and fiberglass reinforced polypropylene tape. It’s easy to cut with scissors and it can be sewn with a standard sewing machine, but it’s very stiff and calling it a fabric is a bit of a stretch. In fact it feels a lot more like a thick aluminum foil which makes it perfect for paper projects. In a recent openMaterials workshop, a group of students cut it into an beautifully intricate shape and used as a touch sensor on the cover of a book. Width: 650 mm (25.5″); thickness: 156 micron; max working temperature: 45°C (113°F); weight: 185 g per sq.m.

:: Velostat: a film made of opaque, volume-conductive, carbon-impregnated polyolefin. The resistivity of velostat decreases when pressured. When sandwiched between two conductive layers, it has a wonderful range for making pressure and bend sensors. Depending on the project, more than one layer of velostat might be necessary, eg. I used 3 layers of velostat to make a pressure sensor that gradually lights up a few strands of EL wire. Thickness: 100 microns; width: 91 cm (36″). Volume resistivity < 500 Ohms/cm. Color: black.

Conductive Threads & Yarns

Conductive threads are made of a combination of either cotton or polyester with alloys of several conductive materials such as silver, copper, tin and nickel. Just as most conductive fabrics, conductive thread is uninsulated making it excellent to connect electronic components to each other or to other electrotextiles. In order to ensure proper connection it should be sewn very tight and with more loops than normally used with regular thread. After some time, conductive thread tends to fray and the stitches to become loose. For this reason I often coat my conductive thread connections with a bit of Wire Glue. Wire glue takes several hours to cure so this coating should only be done after you’re done with all the sewing.

There are several kinds of conductive thread, with significant differences in terms of conductivity/resistivity and fraying, but they are commonly sold in two qualities: 2-ply and 4-ply. The 4-ply contains twice as much metal as the 2-ply, making it more conductive, but it’s also thicker making it harder to thread and sew with. For this reason I usually keep a set of sewing needles with large eyes. The How to Get What You Want and Fashioning Technology websites have some excellent overviews and comparisons of the conductive threads available in the market.

The resistivity of all conductive threads increases drastically with length, making them inappropriate for long connections. For this reason, consider making long connections with ribbons of a good conductive fabric and using the thread only to sew the electronic components to the conductive fabric.

The highly resistive (<1000 Ohm/10cm) silver plated thread offered by Less EMF (cat. #A1226) is good for embroidering fixed or variable resistors.

Conductive yarns are usually made of a combination of polyurethane and inox steel fiber. The resistivity of some yarns increases when the knitted piece is stretched. Again, see How to Get What You Want for great information on conductive yarn.

Special Electrotextiles
:: Textile Perfboard: a fabric base with interlaced rows of thin metal wire.

:: Pressure and Bend Sensitive Fabrics, Tapes and Buttons: made of a layer of insulating knitted or resistive fabric sandwiched between two layers of knitted conductive fabric.

:: Textile Water/Wetness Sensor: detects water by changing its resistance from an open circuit to a few megaohms.

:: EL Wire Tapes: knitted tapes with strands of EL wire weaved into them.

:: Hook and Loop Fastener: similar to velcro but conductive.

Related Materials
:: Wire Glue: even though originally created to replace solder on the connection of electronic components, wire glue is a great material for working with electrotextiles as well. I use it to coat conductive thread knots to prevent them from fraying and also to attach metal snaps to metals that can’t be soldered to.

:: EL Wire: can be basted, woven into or otherwise applied to your soft circuits for illumination.

:: Quantum Tunnelling Composite (QTC): an interesting pressure sensitive material for making textile control pads and keyboards.

:: Metal Sewing Materials: almost all metal sewing supplies, such as snaps and zippers, are conductive and can be used in conjunction with electrotextiles. See oM’s connecting hardware & softwear on soft(er) circuits blog post for some examples.

:: SMD Components: SMD battery holders, LEDs, etc that have flat metal pads are also great for soft circuits. You can solder or wire glue metal snaps or metal rings on these pads to attach them to your circuit.

Starter Kit
I’m often asked what are the first materials one should get to start making soft circuits. Here’s a suggestion for a starter kit:

:: Conductive thread
:: Iron-on conductive fabric or another non-stretch conductive fabric*
:: Stretch conductive fabric*
:: Velostat*
:: Assorted LEDs
:: CR2025 or CR2032 lithium batteries
:: SMD lithium battery holder with flat pads such as this one
:: Non-conductive fabric (felt is my favorite)
:: Sewing supplies: thread, metal snaps, needles with large eyes, needle threader
* Most electrotextiles stores sell conductive fabric sample kits, you can just try one of those instead of buying a larger quantity of the stretch and non-strech conductive fabrics.

Electrotextiles Tutorials by openMaterials
:: Connecting Hardware & Softwear on Soft(er) Circuits
:: Light Up Handshake Glove

Learning Resources
There are many resources for learning how to use electrotextiles. One of the most useful and complete, from a materials and experimentation point of view, is Kobakant’s How to Get What You Want - make sure to check out the sensors and conductive materials sections.

:: Websites w/ Tutorials
Fashioning Technology
How to Get What You Want
Lynne Bruning’s Techniques
Plug & Wear
Plusea
Soft Circuits Saturdays
Sternlab

:: Books w/ Tutorials
Fashion Geek by Diana Eng
Fashionable Technology by Sabine Seymour
Fashioning Technology by Syuzi Pakhchya
Open Softwear by Tony Olsson, David Gaetano, Jonas Odhner, Samson Wiklund
Switch Craft by Alison Lewis

:: Other Interesting Websites
3lectromode
Talk2MyShirt

Main Suppliers
:: Less EMF (USA): conductive fabrics, resistive thread, hook and loop fastener, textile pressure sensitive switches, fabric potentiometer kit

:: Mindsets (formerly MUTR) (UK): conductive fabrics & thread, but make sure to also check out the materials > smart materials section

:: Plug & Wear (Italy): conductive fabrics, textile perfboards, pressure sensitive fabrics, tapes and buttons, textile water/wetness sensor, conductive thread and yarns, EL wire, EL wire tapes

:: Sparkfun (USA): several types of conductive thread

Share your knowledge
If you’d like to contribute content or corrections regarding electrotextiles, please use the comment form below.

>> about the materials 101 series.

MAKING STUFF: Stronger, Smaller Cleaner, Smarter is a four-part PBS television series focusing on materials science:

While reports on “smart materials” or “bionic humans” are familiar enough from TV news and magazine shows, Making Stuff will be the first documentary to provide the basic science behind these and many other technology breakthroughs. Each of the four one-hour public television programs – Stronger, Smaller, Cleaner, and Smarter – will embrace developments in traditional and emerging materials as well as current research in rapidly expanding fields such as nanotechnology and biomaterials. This series will also explore the human stories that helped shape important breakthroughs in the past – the visionary talent, sheer luck, and dogged determination that turned a wild idea into a useful material.
>>Materials Research Society

For more details check out the Materials Research Society and PBS/NOVA websites.

The LumiNet used in a wearable project for Girls' Day 2010

LumiNet is a distributed physical computing framework, developed for physical organic interfaces, simulation of tree algorithms and swarm behavior, and for wearable computing projects. It is a low cost alternative for the Arduino in projects involving hundreds of nodes.

Why Arduino Compatible?
The Arduino has an extensive community with well documented tutorials and examples which makes developing applications simple. Development for the LumiNet should be as simple as for the Arduino. Since the Arduino software did not support the ATtiny family of micro-controllers, one design goal was to modify the existing Arduino framework so that it can be used on the LumiNet hardware.

Network Topology

Three conceptual kinds of nodes can be distinguished: vector nodes, normal nodes, and sensor nodes. They all run on the same hardware and look identical. Vector nodes provide program code for the normal nodes of the network. Normal nodes run the program code that they receive from vector nodes. Sensor nodes can’t be reprogrammed, because they have special hardware connected to their pins and need to run special firmware.

Programming by Infection
Problem: Individually reprogramming every single node for new behavior is tedious.
Solution: If a vector node is detected, the new program code infects all normal nodes of the network like a virus. The program code is stored in the flash memory of the normal nodes and is only updated if a new vector node is connected to the network. This process does not require a PC!

Why Bio-inspired?

The fablab garden is a LumiNet network inspired by nature

LumiNet is a low-cost wired network of intelligent pixels without central control. It should be highly parallel and robust. A bio-inspired / organic network seems to fit this demand. Because it doesn’t have a central controller, it is reconfigurable and supports decentralized stimuli from sensors at any node.

Why Distributed Computing?

The LumiNet jacket features a distributed network of LumiNet nodes

Currently, many advanced wearable computing projects use a centralized computer, with many sensors and actuators wired up to a single microcontroller (often a Lilypad Arduino). Another approach, which LumiNet is well suited for, is distributed computing. Each LumiNet node consists of a three color LED and a microcontroller, and is designed to communicate through wires with up to four direct neighbors.

The Hardware

• 1.2” PCBs
• Bright OSRAM RGB SMD LED
• ATtiny84
• 4 bidirectional communication lines, two pins per line that can implement any communication protocol that uses two pins
• ISP connectors

Communication at Runtime
Organic networks should not have a synchronization clock, because they don’t have a central controller. Without a clock, bidirectional communication in four directions is a problem. Instead of deterministic serial communication, LumiNet uses a organic communication protocol called BYNASE that was developed by Ward Cunningham. It uses noise and requires no precise syncing between nodes. Here is how it works:
* Sender puts pin high statistically depending on the value to send
* Receiver samples pin statistically (but faster than the sender frequency)

LumiNet was developed by Jan Borchers and René Bohne at RWTH Aachen University.  For more information, go to luminet.cc.

This article was written by René Bohne and Amanda Lazar.

Treehugger recently reported on BioCouture, a fashion research project based at Central Saint Martin’s College in London and led by Suzanna Lee, which seeks to grow textiles from a vat of liquid:

The process uses a sugary green tea recipe, to which, a bacterial culture is added. It takes about 2-4 weeks to grow a sheet that is thick enough to use. Sheets are then dried down; either shaped over a wooden dress form–like the ghost dress and ruff jacket –or sewn together conventionally. Depending on the recipe the material can either feel like paper or–more desirably–like a vegetable leather.

In testing with dyes we found no need for mordant [a substance used for dyeing fabrics] and an incredibly small amount of dye goes a long way so it’s eco-credentials go through the entire process. We also recycle a percentage of the fermentation liquid.

vegetable leather grown from a vat of green tea

We look forward to more information about the project and the process. Read more about it at treehugger.

Thanks Rob for pointing this out :)

I keep thinking that even though we tend to use conductive fabric and other soft circuits materials mostly for wearables and such, there has to be much more to it than that. Ayman’s drumsticks are a great of example of other interesting applications for these materials. He made them for his iPad iSteelPan application, but they’ll work on any capacitive surface.

The iSticks are made out of pure copper polyester taffeta fabric (I bet conductive lycra would work really nicely too), metal rod, string, and cotton pads. Check out Ayman’s instructable and make your own!

(via Alicia Gibb)

Last March I had the opportunity to teach an openMaterials workshop at the very special École Supérieure d’Art d’Aix-en-Provence (France). It was part of a larger event in which the school invited researchers and artists from several fields to lead a one week class for 2nd year art students. The goal was to show them different technologies and materials, which they’d later use on an art project. Besides my smart materials class, there was also an astrobiology workshop by Andy Gracie and a video class by Douglas Stanley.

I was so impressed with the work done by these young students that I can’t resist sharing some photos and descriptions of their projects. These were kindly sent by the very talented artist and teacher France Cadet, who guided the students during the making of their final projects.

Barbed Wire by Morgane Guiard
Morgane wanted to represent barbed wire on her art piece. At first she tried to work with fiber optics: the images on the screen were supposed to drive the might to the fiber optics and make the data travel trough. This structure turned out to be really nice and poetic but also very fragile. She eventually broke it and decided to go with red EL wire. This time she put the display behind the barbed wire and made the EL blink according to the speed of the increasing number of victims shown on the screen (the number of victims barbed wire made during 3 different wars).

Interactive Tapestry by Sarah Martinis and Caroline Geneste
Sarah and Caroline made an interactive tapestry (a bit like “toile de Jouy” with some bone sprinted on it). The patterns were fitted with copper electrodes connected to several capacitive sensors. They were playing 8 different yelling sounds and used a sport electronic hacked device with a few electrodes around the wrist.

EL Dress by Amélie Djellel
Amelie used EL wire and a few handmade conductive fabric sensors to create a touch sensitive seethru dress. Each sensor triggered different strands of EL wire shaped inside the dress and representing forms between the meridians, the veins and the organs. The brightness of the EL changed according to the pressure applied on the sensors.

Color Changing Suit & Dance Performance by Lou Feraud
Lou created a suit sprinkled with UV active (color changing) beads and ink. She then wore it during a dance performance, in which she held some UV LEDs at the tips of each finger on one hand, and bright LEDs on the other hand.

Color Changing Stickers by Mélanie Cartier
Mélanie also used UV active ink to create stickers with the radioactive logo to evoke the memory of the radioactive accident and its invisible repercussions.

Animal by Huna Ruel
Huna used conductive fabric sensors to create a little animal that moves when touched (contracting its head and tail). She then covered it with latex. Unfortunately, once dry the latex shrank a bit and caused the sensors to be on at all times.

During the workshop, Amélie and I made some cards with different types of handmade sensors (using paper, conductive fabric, and velostat) to be kept at the school as a reference. The beautiful drawings and neat handwriting are hers :)

Thank you to all the fun and talented students and their awesome teachers France Cadet, Jean Pierre Mandon and Laurent Costes for a really great week!

I’ve learned that there are 3 main challenges in working with soft circuits. The first one is to create circuitry with materials that are almost always completely exposed: a lot of thought goes into the layout of the circuit to not only avoid accidental shorts during normal wear, but also to avoid crisscrosses between conductive materials within the circuit layout. The second one is to think in 3D: more often than not your circuit can’t be applied to a single flat surface and you have bits and pieces spread out over several areas or layers of the piece. The third one is to find ways to connect hardware with soft conductive materials: sometimes you just need to use hard electronic components or a board.

The first two challenges have to be addressed on a case by case basis, but I’ve been experimenting with some methods to address the third that might be useful to others - I’m also hoping for suggestions on different methods and/or ways to improve these :)

:: The curled legs method
This is the classic method everyone working with soft circuits knows and loves. You simply curl the legs of any long leg electronic component, forming a little ring you can then sew to. I’ve used this method with LEDs, transistors (careful, the legs on transistors break very easily), resistors, photoresistors, and even electrical wire.

Since my conductive thread frays a lot and tends to come loose after a while, I usually finish it up with a drop of wire glue (more about this below).

When I really must use electrical wire, which is the case when working with EL wire, I prefer the stranded kind, which is more flexible that the single-strand. In this case, the first thing to do is twist all the small-gauge wires together and then apply a bit of solder to bond them. After forming the ring, apply some more solder to it in order to get a more solid shape to sew to.

:: The wire glue + snaps method
I’ve often found myself in a situation of having to work with conductive pads, which leaves out the preferred curled legs method. So I made a few experiments and found out that wire glue is perfect for these situations. Unlike conductive ink and conductive epoxy, wire glue is very cheap. It’s also easy to obtain and work with. While wire glue is not particularly good as a glue, it is a very reliable conductor.

Gluing the fabric or thread directly to the pads never really worked for me: it comes off too easily and I haven’t found a good way to reinforce the bond. But metal snaps are just perfect for the job!

Metal snaps on surface mount battery holder

I apply a bit of wire glue to the conductive pad and then, using tweezers, carefully place the male half of the snap on top of it. Just the wire glue wouldn’t be strong enough to keep the snap there once you start snapping and unsnapping your circuit. But, after the wire glue has cured (leave it for a few hours), you can add a couple drops of super glue. This doesn’t affect the conductivity or the connection and ensures a pretty strong bond. Once that’s done, you can just add a strip of conductive fabric to the soft part of your circuit and, using conductive thread, sew the other half of the snap on it.

Metal snaps on board

:: The surface mount + wire rings method
This is very similar to the method described above, except that instead of using snaps you’d strip a piece of electrical wire, make a little ring with it, and solder the ring to the contact pads. This is tricky to do on very small components, such as surface mount LEDs, but not complicated at all with bigger pads.

Wire rings on surface mount battery holder

OSLOOM is is a project led by Margarita Benitez aimed at creating an open source electromechanical thread-controlled loom that will be computer controlled. It will include basic software allowing anyone to simply weave a photo thru a web browser (twill/satin), import weave ready files from other software (such as Bhakti/Alice photoshop method), and then post the software on a repository for others to further develop or customize. In addition, all the loom blueprints will be placed online for anyone to build.

A loom is a device used to weave fabric. The loom itself will be a Jacquard style loom. Jacquard looms allow for the individual control of each thread which in turn allows for photographic imagery to be woven. Jacquard looms like this exist commercially but they are very expensive (upwards of $30,000) which puts them out of reach for individuals and small educational facilities.

The OSLOOM could be produced way more economically than that and truly revolutionize what the studio weaver could accomplish. The idea of a DIY open source loom is one that not only artists could benefit from but many individuals and learning centers could gain a resource by building one of these looms as well.

OSLOOM would have an impact on (but not limited to) the following communities/sectors:
artists
DIY/makers
studio weavers
educational
institutions (large and small)
textile designers
developing countries

This project is inspired by MIT’s FabLab concept and other open source hardware projects such as the RepRap and Fab@Home 3D rapid prototypers and the many DIY CNC projects available already.

Margarita is currently working on making available some cardboard tapestry loom plans for lasercutting. Keep an eye on osloom.org for more information!

PS: I’m already imagining textile circuits weaved with conductive thread/yarn :)