Current Work: Laser-Cutting Shape Memory Polymers

I have currently made some hexagonal chiral structures that incorporate color change. Below are pictures of two of these structures that incorporate different color changes.

This chiral shape contains rubine red powder and blue castin craft dye.  The change from purple to blue is depicted here.

This chiral shape contains rubine red powder and blue castin craft dye. The change from purple to blue is depicted here.


This chiral contains blue powder and yellow castin craft dye.  The change from blue to yellow is depicted here.

This chiral contains blue powder and yellow castin craft dye. The change from blue to yellow is depicted here.


I have also been experimenting with using fabric with the colored polymer. Below are pictures of fabric incorporated into the polymer.
This chiral contains rubine red powder with blue dye and blue fabric has been super glued to the back of it.

This chiral contains rubine red powder with blue dye and blue fabric has been super glued to the back of it.


This chiral has blue powder with yellow dye and yellow fabric super glued on the polymer.

This chiral has blue powder with yellow dye and yellow fabric super glued on the polymer.

Current Work: Laser-Cutting Shape Memory Polymers

I recently used a laser-cutter to create a spiral and auxetic shape in the shape memory polymer. After cutting, I placed the material in a hot water bath whose temperature was above 70 deg C. Then applied pressure with my hands and cooled under cold water from the faucet. The results of the spiral and the auextic shapes are given below.

Spiral cut of shape memory polymer using a laser-cutter

Spiral cut of shape memory polymer using a laser-cutter

Heat induced shape change in laser-cut smp.

Heat induced shape change in laser-cut smp.


Extreme heat induced shape change in laser-cut spiral smp.

Extreme heat induced shape change in laser-cut spiral smp.

photo 3 (1)
photo 4 (1)

Auxetic laser-cut of smp

Auxetic laser-cut of smp

Curling heat induced shape change of a 2-coil smp

Curling heat induced shape change of a 2-coil smp

Curling heat-induced shape change of a 3-coil smp

Curling heat-induced shape change of a 3-coil smp

Here is a video of the uncurling of the auxetic amp using a hair dryer: https://www.youtube.com/watch?v=nZGNkn1s4F0&feature=youtu.be

The laser-cutter leaves some burnt edges of shape memory polymer. Also, the integral line segments in the auxetic shape were quite small so did break off when trying to pull them out. For future work, some sanding along the edges could be done to decrease the edge effects from the laser cutter. However, the shape change produced is the desired effect.

Current Work: Shape Memory Alloys

In order to utilize a shape memory alloy, the properties of the alloy need to be known.  Charlotte Lelieveld from the TU Deflt has done work in creating smart composites materials, i.e. materials that incorporate shape memory alloys and shape memory polymers (1-2).  Pictures of her work is given below:

 

Image

Smart Composite using Shape Memory Polymers and Shape Memory Alloys

Image

Prototype of smart composite when the structure is activated


In order for me to create a similar, I need to know the properties of both the shape memory alloy and shape memory polymer. The properties of relevant importance to me are listed below:

Shape Memory Alloys (3):
1. Density (g/cc): 6.5
2. Electrical Resistivity (micro Ohms/cm): 76 (Martensite)/82 (Austenite)
3. Thermal Conductivity (W/m deg C): 18
4. Elastic Modulus (GPa): 40 (Martensite)/75 (Austenite)
5. Specific Heat Capacity (J/kgK): 322

The power to heat the SMA strips, can be found through estimating the energy by (1):

E = Power*time = mass*Specific Heat Capacity* change in temperature

The power may be calculated from Joule’s law:

P = Voltage^2/Resistance

The resistance in each wire is given by:
R = resistivity * length/cross-sectional area

References:
1. Lelieveld, C. M. J. L. (2013). Smart Materials For The Realization Of An Adaptive Building Component. Ph.D. doctoral Thesis, Delft University of Technology.
2. http://materiability.com/smart-composite-shape-memory-materials/
3. http://memry.com/nitinol-iq/nitinol-fundamentals/physical-properties

Current Work: Shape Memory Polymers and Heating Applications

Currently, I am working on incorporation of heating through electronic sources.  I have made a sample that contains 20 guage nichrome wire from Jacobs.  The data on the wire is given below:

Data for varying guage lengths of Nichrome wire

Data for varying guage lengths of Nichrome wire (1)

From this data, I used Mathematica to curve fit to a second order polynomial.  The equation for the polynomial is given as:  Amps = 7.55359*10^-6*T^2+0.00549092*T+2.47994.  An image of the curve fit data is given below:

Amperes vs. Temperature curve for 20 guage Nichrome wire

Amperes vs. Temperature curve for 20 guage Nichrome wire

For the 20 guage nichrome wire, a temperature of 30 deg C can be obtained with the application of 2.65 Amps.  The sample with the nichrome wire, as well as, a sample that contains carbon black, and a sample that contains embedded shape memory alloy is seen in the picture below:

Top Left:  Shape Memory Polymer with Embedded Nichrome Wire, Top Right:  Shape Memory Polymer with Embedded Carbon Black, Bottom Left:  Shape Memory Polymer with Embedded Shape Memory Alloy

Top Left: Shape Memory Polymer with Embedded Nichrome Wire, Top Right: Shape Memory Polymer with Embedded Carbon Black, Bottom Left: Shape Memory Polymer with Embedded Shape Memory Alloy

Note that the weight percentage of carbon black is too high, and the sample created was a gummy consistency.

References:

1.  http://jacobs-online.biz/nichrome_wire.htm

Current Work: Shape Memory Polymers with Color Change

I recently tried again to incorporate more Solar Color Dust colors into a shape memory polymer.  I made four samples of the following ratios:  1.57 ml Epon 826/2.43 ml Jeffamine/3.12 ml NGDE.  This ratio corresponds to a glass transition temperature of approximately 40 deg C.  For these samples, the Solar Color Dust was mixed according to the instructions per the website (10 grams of dust to 1 pint of epoxy).  Three of the samples contained just Solar Color Dust and epoxy, while the fourth contained Solar Color Dust, epoxy, and Castin Craft blue dye.  Pictures of the samples are given below for heated and unheated specimens:

Shape Memory Polymers with Embedded Color Powders and Dyes After Curing

Shape Memory Polymers with Embedded Color Powders and Dyes After Curing

Left to Right: Castin Craft Blue Dye and 0.24 g of Rubine Red Solar Color Dust, 0.24 g of Magenta Solar Color Dust, 0.26 g Sky Blue Solar Color Dust, 0.22 g Green Solar Color Dust

Left to Right: Castin Craft Blue Dye and 0.24 g of Rubine Red Solar Color Dust, 0.24 g of Magenta Solar Color Dust, 0.26 g Sky Blue Solar Color Dust, 0.22 g Green Solar Color Dust

I took each of the samples and added some heat with my hand.  The result is given below:

Castin Craft Blue Dye with Rubine Red Solar Color Dust with Applied Heat from My Hand

Castin Craft Blue Dye with Rubine Red Solar Color Dust with Applied Heat from My Hand

Magenta Solar Color Dust with Applied Heat from Hand

Magenta Solar Color Dust with Applied Heat from Hand

Sky Blue Solar Color Dust with Applied Heat from Hand

Sky Blue Solar Color Dust with Applied Heat from Hand

Green Solar Color Dust with Applied Heat from Hand

Green Solar Color Dust with Applied Heat from Hand

From this experimentation, Rubine Red seems to give the most significant color change out of all the powders an hand.  Also, from the first picture, you can see that there is some clumping inside the epoxy.  This clumping is due to the fact that the powder is not well dispersed within the epoxy.  Therefore, may next time sonication might be used to disperse the particles.  Since, I had some extra material left over, I mixed the Magenta, Sky Blue, and Green epoxy mixtures together and obtained the following result:

Mixture of Green, Sky Blue, and Magenta Solar Color Dust with Epoxy

      Mixture of Green, Sky Blue, and Magenta Solar Color Dust with Epoxy

 

Mixture of Green, Sky Blue, and Magenta Solar Color Dust with Epoxy and Heated with Hand

Mixture of Green, Sky Blue, and Magenta Solar Color Dust with Epoxy and Heated with Hand

Note when all three of these colors are mixed together and not dispersed, the coloring is very beautiful and unique.  However, due to lack of the dispersion, when heat is applied with the hand, not as visible of change is seen in the sample.

Current Work: Experimentation with Shape Memory Polymers Using Color and Wire

I have been working on experimenting with incorporation of color and wire into the shape memory polymer matrix.  I would like to create color and shape change as a part of biomimictry sculpture.  To experiment, with color I used a product called Solar Color Dust (1).  This product is a micro encapsulated powder that changes color upon the addition of heat or light.  I mixed the Solar Color Dust in accordance with the instructions on the website:  10 grams to 1 pint of clear base.  The result of the mixing turned out well, the polymer appear to have a hard shape upon removal from the mold.  A picture is given below:

Shape Memory Polymer with Solar Color Dust

Shape Memory Polymer with Solar Color Dust

I also experimented with the addition of Castin’ Craft Transparent Dyes (2).  This is an ether based dye that can be purchased at Hobby Lobby.  A few drops were added to the mold to change the color from clear to blue.  The finished product appears to be pretty flexible at room temperature, it could be due to addition of an ether inferring with the mix ratio of the polymer itself, or other factors.  For future work, I will try using less drops in the polymer.

Shape Memory Polymer with Castin' Craft Dye

Shape Memory Polymer with Castin’ Craft Dye

The last experiment was trying to incorporate wire into the shape memory polymer.  The wire was sunk down into the mold and taped.  However, because of the high temperature cure of the system, the tape was not sufficient to anchor the wire and the wire moved during curing.  Also, the result below is given of the polymer.  Since, the wire was stripped, the excess heat from the wire might have caused the polymer to become very pliable and in turn not hold its shape.

Shape Memory Polymer with Wire Incorporated

Shape Memory Polymer with Wire Incorporated

References:

1.  http://solarcolordust.com/

2.  http://shop.hobbylobby.com/products/green-transparent-resin-dye-761650/

Guest Diffusion in Polymer Materials

In the use of polymer materials, a significant number of research employ what is called “guest diffusion” in order to “dye” the polymer material a different color.  This process occurs based on polymer membrane selectivity due to the following factors:

  1. separation of differential solubility of guest molecules at the surface of the membrane (known as sorption)
  2. varying diffusion characteristics of different guest molecules or ions across the membrane
  3. desorption of molecules or ions on the other side of the membrane

For gas and liquids factors 1 and 2 are vital, while in ion transport all three factors are influential.  An example of the mechanism described in (1) is that hydrophilic molecules will dissolve in a hydrophilic surface faster than hydrophobic molecules.  However, in general, specific functional group determine solubility, attachment and entry into the membrane.  When diffusion occurs through a solid polymer, it is dependent on affinity and available space between chains.  In these cases, the molecular space can be influenced by whether the polymer is above or below the glass transition temperature.  When it is above Tg, greater chain movement is allowed, and therefore more free volume and permeability change for certain guest molecules.

The top label indicates the polymer membrane.  The left hand barrier is the sorption zone and the right hand barrier is the desorption zone.  The dots represent the molecules passing through the system.  The transmission of molecules across a membrane can be understood in terms of three processes--sorption, diffusion, and desorption--with separations accomplished if different molecules in a mixture respond differently to any of these three processes.

The top label indicates the polymer membrane. The left hand barrier is the sorption zone and the right hand barrier is the desorption zone. The dots represent the molecules passing through the system. The transmission of molecules across a membrane can be understood in terms of three processes–sorption, diffusion, and desorption–with separations accomplished if different molecules in a mixture respond differently to any of these three processes.

References:

1.  Allcock, H.  Introduction to Materials Chemistry. Hoboken, NJ:  Wiley, 2008.