Inspired by a paper we read last week, I attempted to produce a conductive silicone elastomer. While the paper used a variety of conductive fillers—silver, aluminum, nickel—I was limited by the materials on-hand, and decided to focus on nickel, which was available in the lab, and gives fairly good conductive results.

I mixed a number of silicone samples using two different conductive fillers at a range of volumetric percentages. After letting the silicon, none of the samples were shown to be conductive.  This indicates procedural or technical problems in my implementation, which diverged from that in the paper’s.

Substrate

SkinRITE10 Base & Catalyst

To cast the silicone, I used SkinRITE10, a two-component silicone frequently used for casting. It consists of a silicone base and a catalyst to begin the curing process.  10 parts base are mixed with 1 part catalyst, and the silicone cures over the course of several hours. It is widely-available.

Conductive Filler

Novamet Nickel Flake HCA-1

The datasheet indicated that these nickel flakes were manufactured specifically for conductive applications, and had been specially-treated to prevent oxidization.  Each flake is milled to be 1 micron thick, but has a 14-16 micron diameter. The manufacturer suggests that this allows for a great deal of surface contacts to be made. It is typically used in conductive paints.

Novamet HCA-1 Nickel Flakes

Novamet 60% Nickel Coated Graphite

To get a better sense of relative conductivities, I also used nickel-coated graphite. Having had some experience with carbon conductors, I was curious how this material would behave. The primary application of this substance, though, is in shielding and I expected to see less conductivity than with the pure nickel flakes.

Novamet Nickel-coated Graphite

Procedure

Using the calculated density of the conductive fillers—1.45 g/ml for both—specific volumes of filler were weighed out. Volumetric ratios of 20%, 30%, 40%, and 50% filler were calculated and weighed.

Weighing Filler Samples

Each was combined with 5ml of catalyzed silicone and mixed together as vigorously as possible with a toothpick. A mold with cavities of 5ml was cut using a laser cutter. The resulting mixture was spread across a mold and allowed to cure. The resistivity of the cured silicone panel was the tested with a digital multimeter.

Cast & Curing Silicone Panels

Challenges

Mixing up silicone is a messy process, as is measuring and preparing the fine filler samples. The quantities involved are small, and it is difficult to maintain accuracy. The SkinRITE silicone takes about a day to cure,.

Outcome

No samples were tested as conductive with a digital multimeter. A number of conditions were attempted—stretching, compressing, piercing the silicon panels—all unsuccessful. There are a number of possible factors, many of which are discussed in the relevant paper:

• Insufficient filler concentrations to achieve conduction
• Inadequate agitation of filler-silicone mixture
• Overly-elastic substrate which does not compress filler into a conductive lattice
• Oxidization or corrosion of powdered filler
• Procedural issues in the preparation of the SkinRITE silicon
• Inconsistent casting and conductor distribution

Testing the conductive silicone mixture

Going Forward

The first step will be to attempt to repeat the experiment with higher concentrations of conductive filler. I would also like to improve the consistency of the casting, to acquire thin, uniform sheets.  A useful, controllable, highly-elastic conductive substrate could be poured and cast in many different shapes and forms. It could be used to coat other materials, or form conductive contacts on unusual or ‘squishy’ forms.

I’m interested in redesigning some ordinary objects into interactive projects. By doing this, the old staff will be given a second life. So, this time I’ve tried to experiment conductive fabrics and threads to make a signal tool with a glove.

Inspiration

People used to expressing feeling by making gestures. And, it’s interesting to find that the gesture signs actually go over different languages. Thus, I got the idea of making an interactive glove signs these universally used hand gestures.

Category

After having a study with gesture, my first step was classifying some gestures with different meanings that are commonly used through people’s conversations.

Then, I was thinking to use the contact points as the switches in the circuit for controlling the whole connection. The idea is that these LEDs will be shining when particular points contact. By making each gesture, different color’s LED on the glove would be turned on as a sign.

Materials

A glove, needle, conductive thread, stretchable conductive fabric, 3 LEDs, battery, battery holder…

Circuit

Working in progress

Before I started to put the materials on glove,  the first successful attempt was a test of the circuit and materials to see if they are all working when connected.  Then I began to move the materials on glove.

Project

You can find the final project and how it works through the video posted here

Singal Glove prototype video

Potential application

This idea can be applied for communication with sign language for special needs.

e.g. For disabilities with problem of speaking and listening; For traffic guidance.

Dena Molnar and Nicole Tariverdian:

Thermochromic paint and pigments have the ability to change color when heated. For this first project we decided to experiment with dying yarns with Thermochromic pigments. Originally we thought we might have to boil the pigments to create the dye.  This was concerning since  boiling the pigments could potentially desensitize or denature the pigments  causing a lose of  their reaction to heat.  After a little research we found a dye recipe that used vinegar to set the color (similar to how easter eggs are dyed. You can find the recipe here. While using this recipe worked, there were aspects of the solution that require further research for permanent thermochromic/ and or dyed applications. We discuss this in detail under Chemical/ Material Notes.

Our intent was to create the yarn and apply it in different functions including knitting and weaving. We hoped to control the color and patterns though blending the thrmochromic yarn with a conductive yarn. Once woven or knit together an electrical current is run though the swatch heating it and changing the colors in isolated areas.

Process:

Dyeing:

Using the thermochromic paints in the lab as well as Dena’s personal supply, we dyed  three different yarns; one multi colored, one pink and one yellow. After dyeing the the yarn we left it to dry for a few days. Even after several days the wool retained moisture. To dry the yarn we used a hair dryer.  During the drying process, the yarns changed colors, which was exciting to see.

Knitting:

Once the yarn was completely dried we began to wind it and ply it with conductive stainless steal yarn to prepare for knitting. We wanted to knit one sample with the stainless steel plied with the thermochromic yarn and one using a pick on pick technique. We encountered several issues with the knitting machine and the stainless steel yarn making this process much more complicated then we initially hypothesized. The stainless yarn is not easy to work with on the knitting machine, as  it snags and kinks and eventually breaks. When using it with the machine you have to go slowly and be carful of any snagging.

Our initial sample was created by knitting with he multi colored yarn in conjunction with conductive yarn, run though at the same time on the knitting machine. The second sample we created consists of the thermochromic yarn plied (using a drop spindle) with the stainless steel. We tested both swatches and observed the patterns created when hooked up the the power supply. After testing each we decided to felt the second swatch.  Once felted we observed that the die during felting either washed out or became less sensitive.

Obervations:

Using a 12V Adaptor, we observed a complete surface color transformation on the knit that just used wool and steel yarns knitting together (These were not plied beforehand; they were simply fed into the knitting machine at the same time). We noticed a more random surface change on the knit that used a plied steel/wool yarn knitting with a cotton. This may be due to the cotton breaking up areas of conductivity.

Check out the video

Applications:

While knit constructions call to apparel applications, we are interested in instances where the conductive yarn has the potential to influence the thermochromic yarn, and not the (just) the heat of one’s body.

Taken into the knit or woven realm, we could see this applied to interior applications such as upholstery, and wall or window applications . The conductive yarn could be actuated with the use of a micro controller uploaded with information regarding external conditions, such as weather. Changes in weather , for example,could activate changes in the color and surface pattern of the textile revealing a secondary pattern that corresponds to the outside data .

Chemical/Material Notes:

There are a few aspects of the chemicals, materials and dying process that would benefit from further explanation and investigation if you plan on trying this yourself.

Thermochromic pigments- The pigments we used, were in deed “pigments”, not dyes, (the most well known Thermochromic dye is Leuco dyes) and we there fore had to make a solution to dye our wool skeins. This process, was, in reality a hybrid of standard processes for dying different types of yarns.

Direct , Acid, and  Disperse dying

Direct Dyes- A class of dyes largely used for dyeing cellulosic (as opposed to protein or synthetic) fibers, are water soluble and can be applied directly to the fiber from an aqueous solution.  The term may also be applied to dyeing without the use of mordants to fix the dye once it is applied. Direct dying often require boiling the yarn in a dye bath.

Acid Dyes- Are a class of dyes most commonly used for dying wool or protein fibers. Acid dyes are thought to fix to fibers by hydrogen bonding, Van der Waals forces and ionic bonding. They are normally sold as the sodium salt  therefore they are in solution anionic. Protein fibers and synthetic Nylon fibers contain many “cationic” sites therefore there is an attraction of anionic dye molecule to a cationic site on the fiber. The strength of this bond is related to the desire/ chemistry of the dye to remain dissolved in water over fixation to the fiber.

Disperse Dyes- Used most often in the dying of Synthetic fibers.

Things to try- We essentially used a direct dying solution, omitted part of the process (boiling), and on a Protein (wool) fiber, which is a possible reason for the dye washing out during felting (if not caused by exhaustion of the thermochromic properties of the pigment). Below is a list of suggestions for further investigation.

- Locating the original Leuco dyes or researching if there is a safe “acid dye solution” that one could add thermochromic pigment to.

- Boiling the undyed wool yarn to open up the fiber and remove additional oils prior to pouring the thermochromic pigment/solution on may help the wool to accept the dye.

-Using the thermochromic pigment/solution on a cellulosic  yarn instead of a protein. In this case, the material is probably more compatible with the process we used.

- ProChem is a fantastic dye resource, located in MA, which may have primers available to help fibers accept dyes and pigments, as well as an extensive range of dyes discussed above.  http://www.prochemicalanddye.com

I followed up on last week’s assignment to see if commercially available metal-filled polymers might be conductive and might be flexible enough to use as either a thin conductive plate or, when applied to a piece of paper, form part of a conductive paper material.

I bought JD Weld’s Steel Stik, a steel-filled non-rusting epoxy, JD Weld’s Kwik and a Commercial Electric auto-range multimeter.

I started with the Steel Stik, a putty stick with a consistency not unlike stiffened dough.

The surprise for me is that the material is unmixed. The steel putty is at the core, surrounded by the hardener. The instructions require kneading the required amoun until thoroughly blended, before use.

The knead mixture cures in 5 minutes and under, and one must work quickly in order to shape it into its desired thickness and shape. The first time I tried, I took too long, and it hardens into a solid, inflexible compound.

Using a rolling pin, I tried to spread the mixture out as much as I can, but I did not get very far. It retained a thickness of approximately 2.5 to 3mm. At this thickness, the cured steel-filled epoxy was not flexible at all, and I don’t imagine that it would be useful either has a thin plate conductive surface or blended in with other non-polymer materials such as paper pulp.

What was a surprise was its conductivity. Using the multimeter set at the mega-ohms range, it gave no reading at all.

I tested a second material, the Cold Weld, which in its liquid form is much more easy to spread.

I manage to spread this into a layer approximate 1mm thick. Once this is cured, there is some flexibility, but not so much that it can bend without breaking. It too gave no reading at all on the multimeter. From a link discussing similar materials on the 3M website, conductivity of suitable metal-filled polymer surfaces is only in the order of 10⁹ to 10¹¹ ohms/square.

I was interested in taking a pure element of nature, such as a beautiful flower, and transforming it into a technical matter. By covering the flowers in copper paint, the conductive material trapped the live flowers in time, allowing them to keep their shape despite their eventual death. I originally kept a third flower in its natural state, but it died within one day, which is when I decided to paint it in copper as well. Sadly, this project proves to be ethemeral. Day-by-day, the flowers slowly crumble to their demise as the copper chips off and the petals can no longer withstand the weight of the paint. Their temporary state, however, is still transformative.

Initial Activities:

Painting flowers is a messy activity. They must be painted upside down. It is easiest to hang them from a clothes line. I left them overnight to dry before continuing the process.

Challenges attached the LEDs to the flower:

I tried various technique to attach the lights to the flowers:

1. I tried sewing onto the vein of each flower petal. The petals adamantly rejected this notion.

2. I tried sewing the lights onto the leaves. They also rejected the idea.

3. I tried taping the Lilypad LEDs onto the leaves. The copper take is not conductive on the sticky side. Therefore the lights would not always turn on, even when correctly wired.

4. The last attempt – and luckily it was successful – I soldered tiny little LED lights onto the copper, which I eventually stuck onto the backside of the leave.

The Final Result:

The final version was a bit different from the original idea. I ended running the copper tape up the side of the stem, eventually connecting with the copper flower. That way, when I touch the leaf to the copper flower petals it closes the circuit and the lights turn on. Originally I wanted to contain everything on the leaf itself. As the flower started to dry, it became more fragile. This made it difficult to keep playing around with different techniques. I chose the least invasive way, as it was literally crumbling in my hands by the end. Although it was exciting to work with a live object, its death is depressing. I may choose to work with an inanimate object next time and would suggest others to first experiment on a fake flower.

Failures:

sewing LEDs onto a flower

sewing LEDs onto the leaf

finding a good solution to place the battery on the bottom of the flower

infinite preservation instead of ephemeral art

ITO Glass

Conductive Play Doh

How To: Conductive & Insulating Play Doh Recipe
Tools:
large mixing bowl
rolling pin
wax paper
non-stick saucepan
ziplock bags
whisk
wooden spoon
cookie sheet
small bowls
sponge

How To: Conductive Play Doh
Main Ingredients:
1-cup of water
1.5-cups of flour
¼-cup of salt
3-tbsp. of cream of tartar
1-tbsp of vegetable oil
food coloring

1) mix water, 1-cup of flour, salt, cream of tartar, oil, and food coloring in bowl
2) transfer to pot, cook over medium heat, & stir consistently
3) stir mixture until chunky; will form a ball in the middle of the pot
4) place dough on floured surface, flatten with a rolling pin and knead remaining flour into the ball until a desired consistency is reached
5) store in an airtight container or plastic bag

How To: Insulating Play Doh
Main Ingredients:
1.5-cups of flour
½-cup of sugar
3-tbsp of vegetable oil
½-cup of distilled water
food coloring

1) mix 1-cup of flour and all other solid ingredients and oil in a bowl
2) thoroughly stir in 1-tbsp of distilled water; repeat until majority of water has been used
3) once mixture has reached a lumpy state, knead into one ball
4) place dough on floured surface, flatten with a rolling pin and knead remaining flour into the ball until a desired consistency is reached
5) store in an airtight container or plastic bag

Testing 123: Conductive & Insulating Play Doh
Tools:
3-mini 3-volt LEDs
(preferably red, yellow,
and green)
9-volt battery
soldering iron
rosin-core solder
mini alligator clips
9-volt battery holder

Testing 123: Basic Circuit
• after soldering the alligator clips to the battery holder, insert the battery
• create a circuit by separating conductive dough with insulating dough
• stretch the leads of an LED into the respective +/- globs of dough

click here to see the basic circuit work!

Resistive Properties

Potential Applications
•use conductive and inductive play doh as a grout for ITO glass
•create conductive stained glass or soft sculptures
•for more ideas, check out Squishy Circuits: http://courseweb.stthomas.edu/apthomas/SquishyCircuits/index.htm

Complications
•non-uniform sputtering on ITO glass
•corrosive salts in conductive play doh eat away at metals
•consistency of conductive vs insulating play doh are different
•shelf-life of insulating play doh is shorter than conductive dough

Next Steps
•test if hardened doughs are still functional
•mix in metals such as graphite into conductive dough
•create a longer-lasting insulating dough
•revisit ITO glass; consider reapplying ITO or other transparent conductive material over glass

ENJOY!

I wanted to experiment with a natural material that can be found everywhere. I decided to use a leaf because it had a beautiful surface with vines that resembled electrical circuits. It is also often wasted if not used. I experimented with how various conductive materials behaved on a leaf and finally formed an electric circuit on the surface of the leaf.

Conductive Ink

Conductive ink was drawn on a piece of leaf to create an electrical circuit using a wooden stick dipped in silver ink. Brush made it difficult to control precision; pen often scratched the surface of the leaf and did not provide enough ink flow. Compared with other conductive material, the conductive ink adhered to the surface of the leaf the best, but did not connect to the microcontroller and battery very well. Silver ink painted using a stick was the most effective.

Copper-plating

Each circuit was then copper-plated separately. Time spent in copper bath directly determined the color of copper plates. For example, 3 minutes in bath yielded a dull copper color while 10 minutes in bath resulted in a bright copper color. Plating surface also determines level of adhesiveness of the copper. For example, the copper on the stem adhered well to the surface; however the copper on the leaf was fragile and broke off easily when the leaf was scrunched. The copper circuit that fell off was glued back. Electrometer also showed that silver ink was more conductive than copper. The resistance of silver ink was 0.0-0.1 Ohm and the resistivity of copper was 0.2-0.3 Ohm.

Conductive thread

Conductive string could be a substitute of ink and copper. However it broke the leaf easily. The surface of the leaf was too fragile. The metal-coated string was rougher and broke the leaf easier. This method was not pursued in the final product.

Connecting the circuits

Microcontroller and battery were connected to the circuit through soldering and conductive ink. Soldering provided a stronger bond than conductive ink and glue especially due to the slippery surface of the leaf.

The circuit will be completed when the user touches the input (the stem) while holding on to ground. Both are copper-plated for easy identification. The LEDs turn on and off when the input is touched. Video.

Challenges

Overall, fresh leaves were a difficult surface to work on due to its fragility and slippery surface. This could possibly be solved if the leaf was dry. Soldering provided better connection than ink alone.

Potential application

This could be used in an interactive installation where synthetic fabric leaves are attached to a real tree and people can touch individual leaves (inputs) and lights will turn on and off depending which input the user touches.

Download a copy of the presentation here.

I used wool yarn to create a swatch of felted conductive material, testing its relative resistivity in the felting process. I also used wool rovings to create large felted strands, like dread locks—good candidates for silver thread. The former yielded a good object lesson in the properties of silver thread; the latter was mostly an opportunity for experiments with soldering and LEDs—let’s just say I know more about what *not* to do now.

If the purpose of having several projects in a semester is the chance to learn from mistakes, especially early on—well, then, this was a spectacular success.  I used great materials, and these conductive combinations have a lot of application possibilities. But I was far too cavalier about my understanding of conductivity measurement to get meaningful results (see below). Nonetheless, I got my feet wet in a number of material and electrical techniques. I’m looking forward to that SparkFun order I have coming in the mail…

For the main project, I started with this thick 100% wool yarn:

It knit up beautifully into a scarf-like strand:

And then I threaded silver conductive thread through the stitches, like this:

I made four lines of thread, leaving most of the tails long at the end to observe the changes in the threads themselves:

I was hoping to have the silver thread sufficienctly felted into the wool that it would end up invisible. You’ll see below that this didn’t work; my first mistake was these too-long stitches that wrap around the knit stitches. In the future, I’d thread them much more tightly into and through the knitted wool stitches, for a more complete, homogenous product.

Unwashed, I measured 24.3 mega Ohms of resistivity.

For the first felting, I used a rinse-and-spin cycle was to the threaded strand: The speed wash, hot/cold water, extra high spin speed. A 12 minute cycle. I measured 22 mega Ohms at this point, but the short wash hardly made a dent in the form of the piece:

I put the piece in for a second wash—again on hot/cold, but this time a full cycle (Quick Wash), with normal spin to go easier on the machine. This tightened up and blended the yarn stitches quite a bit, and damaged and frayed the strands of silver thread, as you can see at the tail end:

On the top side of the swatch, the threads weren’t visible, but this bottom side, with its overly-long stitches, still had these frayed and loose bits, not nearly as incorporated as I would have liked to see. Resistivity increased in the process, likely due to the breakdown of the thread with the vigorous action of washing/felting. I measured 33.8 mega Ohms after this second wash. Given the simple corrections that would make this a fairly coherent material, without too great a loss in conductivity, this composite is pretty promising for applications.

The second project I experimented with began with these wool “rovings”—thin strips of wool, nearly formless, like cotton candy. But with a quick soak in hot water and wool soap, and tight rolling action, they became sturdy, cigar-like strands:

With Leah’s help, I then explored some possible ways to make a whole sensor-to-actuator system here—which ended up being a tutorial in soldering and ways to handle tiny and delicate LEDs. Here’s as far as I got by 6 pm Sunday:

It was good to get this far, if just to see what kinds of material options would make this happen. Here I’m using a usually-less-desirable kind of conductive thread—it has frayed and “hairy” edges, meaning its carrying power is more unstable. For motion-sensitive dread locks, however, that instability could be a virtue.

I’d need an insulated thread for the uninterrupted circuit, so I started piecing together the ends of the insulated thread and the metal thread with crimp beads to create a holder for a small LED. But my unpracticed skills with soldering tiny parts led only to much breakage. I’d like to finish this project just to see these work.

This project is an investigation of materiality and embedded conductivity. The base material is SkinRite10 which is a silicon rubber product that is translucent and highly elastic. The embedded conductivity is achieved with 3V coin battery, wire wrapping wire, and LEDs. 2 prototypes were developed during the process: first, a simple elastic button which lights up when pressure is applied and second, a 3 dimensional puzzle that only lights up when it is configured correctly.

This is a video of configuring the puzzle pieces together to create the lighting effect. A better conductivity is achieved when pressure is applied and the circuit is only completed when the pieces are assembled correctly.

Mold geometry and laser cut templates

Mold fabrication: The mold is created using a combination of Plexiglas (1/32″ thick) and chip board (1/32″ thick). The geometry is based on a box with an undulating surface on top which is sliced up with curved surfaces. The undulating surface is unrolled and grooves were created for easy deformation as well as to give texture to the top surface.

Casting: The casting material is SkinRite10 which is a silicon rubber product that is translucent and elastic when fully cured. The product uses tin as catalyst and can be cured in room-temperature within 24 hours.
Circuit: 9 coin batteries and 9 standard red LEDs are soldered/ taped together in a series array. In order to complete the circuit, all the connections (total 12) need to be in contact with each other.

Elastic Button: When pressure is applied, the battery and LED that is embedded in the material is connected and the LED lights up.

Elastic Puzzle: When the puzzle pieces are assembled, the series array of batteries and LEDs are completed and the puzzle lights up.

Further development in the method of embedding the electrical components into the casting material will improve the final product. The current design of the Elastic Button doesn’t allow the battery to be replaced unless you physically cut it out. However, for the Elastic Puzzle, it is possible to replace the battery but since it is not embedded before the cast was cured, the assembly is not clean and water tight (compared to the Elastic Button). Possible areas of implementations are electronic products that require soft materiality for safety and/or waterproofing.

The Conductive LEGOs project was an attempt to create conductive LEGOs.  Through this process, I got to explore the method of electroplating materials.  Electroplating is the act of coating ordinary non-conductive materials in a metal (such as copper).  This allows anything to be used to build a circuit.  The way electroplating works is that the object you want to coat is first painted in conductive ink.  Then, the painted object is put into a corrosive bath and connected to a power supply.  In this corrosive bath is also a copper rod connected to the power supply.  As the corrosive material eats away at the copper rod, the flow of electricity causes the copper atoms to flow to and adhere to the conductive ink coated object.

My first attempt was a dismal failure.  I only painted the dots on top of the LEGOs and the spaces they go into under the LEGOs.  Unfortunately, this did not provide enough contact between the LEGOs and only singular spots got plated, as you can see below.

My next attempt was more successful.  This time, I painted the bottom edges and the top part of the  LEGO, around the dots.  This time, I was more successful in plating the LEGOs and actually making a conductive connection between them.  Unfortunately, my success led to another problem: the copper peeled away from the LEGO.  My copper layer was too thin and sparse to firmly attach to the LEGO pieces.

My third attempt was excellent.  Using a few suggestions, kindly offered by others in the lab, I sanded the LEGOs using rough (~ 100 grit) sandpaper to make the LEGO surface more smooth.  Also, I spread a thicker layer of conductive ink all over the LEGO.  After 3 to 5 minutes in the corrosive bath (more than that and the LEGO plastic starts to burn/melt), the LEGO pieces were conductive and robust.  They have a resistivity of about 0 ohms (makes sense because they are coated with copper).  Though it is a little difficult to click the pieces together, it can be done.

I can think of a few applications that this can be used for in the future.  For example, there are all sorts of LEGO kits out there that incorporate electricity.  It would be wonderful if your design isn’t limited by the length of wire you have available.  Instead, you can just use the LEGO pieces as the electrical connector between components.

Presentation: Conductive LEGOS